Category Archives: New Research

Effects of Age- and Sex-specific Density on Behaviour and Survival of the Brown Anole

A perching brown anole.

An adult male brown anole.

Greetings anole biologists and enthusiasts! I write to you from Fred Janzen’s 30-year field site along the Mississippi River in northwest Illinois, where I’m collecting data for my dissertation studies. Unfortunately, there aren’t any anoles here, but the painted and common snapping turtle densities are impressive. Fortunately for this post, however, current field work has been paused as a team of inmates are cleaning up debris from recent flooding of the area. Thus, I’ll give a brief update on the last chapter of my master’s research with Dan Warner and the brown anoles* of northeastern Florida.

A good bit of Anolis work has shown that species partition perch height and width to reduce competition. However, less work has focused on habitat partitioning within species of anoles. Thus, my thesis work examined whether similar partitioning exists between age and sex classes of the brown anole, and attempted to identify the drivers and mechanisms of such age-specific habitat use. First, we found that juveniles on Dan’s study islands perch on lower and thinner perches, and use the ground more frequently, than adults (discussed in another Anole Annals post). We then altered the density of adult males in mesh enclosures in the lab, and found that juveniles perch lower in the presence of adult males and have a greater response as adult male density increases (discussed in another Anole Annals post also).

Fig 1

Juvenile Anolis sagrei survival in response to adult male and female density (F4, 164 = 3.67, P = 0.0069).

Quite excited by our findings that adult male density influences juvenile microhabitat choice, we set up two field experiments to assess 1) how adult male and female densities independently affect juvenile microhabitat use and survival, and 2) how juvenile presence affects adult male and female microhabitat use. Interestingly, we found that after just four days of exposure, adult male, but not female, presence reduced juvenile survival (Fig 1). However, we found no evidence that juveniles shifted microhabitat use behaviorally, nor were juveniles selected against in a pattern consistent with the observed age-specific habitat use in the field (e.g., selection favoring low perching juveniles) in response to either adult males or females. One large difference between the lab and field experiments is that the lab experiment used larger juveniles than the field experiment. Perhaps the smaller field juveniles innately perched in safe microhabitats, thus reducing their ability to behaviorally respond to adult threats. In addition, strong past selection favoring low perching hatchlings may have reduced the phenotypic variation needed to detect any selective patterns. The second field experiment revealed that adult microhabitat use is not affected by the presence of juveniles.

This last chapter has recently been published and is freely available through this link until 25 July 2017 (Delaney and Warner. 2017. Animal Behaviour 129:31-41). After that, shoot me an email.

For now, I’ll be studying fitness tradeoffs in maternal investment strategies in turtles. However, once an anologist, always an anologist. So I’ll keep an eye on Anole Annals to get my Anolis fix, until I find my way back south.

Happy noosing!

*Note – I’m certain that “Dan Warner and the Brown Anoles” should be a band name.

 

Phylogeny and Diversity of Monkey Lizards, Anoles’ Closest Relatives

polychrusm

Monkey lizards (Polychrus) are unique among Neotropical arboreal lizards in having strikingly long whip-like tails, as well as long limbs and digits. Interestingly, they resemble Old World chameleons in both morphology and behavior: slow-moving lizards with a laterally compressed body and cone-shaped eyes with partially fused eyelids. Although their phylogenetic position in the iguanid tree of life remains controversial, many authors argue that monkey lizards are the living sister taxon of anoles.

In a study published last week in PlosONE, we present a molecular phylogeny of all eight currently recognized species of Polychrus based on the largest geographic sampling to date. Our species tree places P. acutirostris as sister to all other species of Polychrus. While the phylogenetic position of P. gutturosus and P. peruvianus is poorly resolved, P. marmoratus and P. femoralis are strongly supported as sister to P. liogaster and P. jacquelinae, respectively. Moreover, recognition of the recently described P. auduboni and P. marmoratus sensu stricto as distinct species suggests that the populations of “P. marmoratus” from the Amazon and the Atlantic coast in Brazil represent separate species. Finally, species delimitation analyses suggest, among other things, that the populations of P. femoralis from the Tumbes region (southwestern Ecuador and northwestern Peru) might belong to a cryptic undescribed species.

Print

The Evolution Of Morphological Diversity In Tropidurine Lizards: the Influence Of Habitat

AA1

Uracentron flaviceps (upper photo) and Microlophus thoracicus (lower photo), two tropidurine lizards adapted to rainforests and deserts, respectively.

I was lucky enough to spend some months working at the Museum of Comparative Zoology of Harvard as part of the Losos lab. There I learned a good deal about anoles and got to meet anole-loving people face to face. Even though this atmosphere tempted me to develop a project related to one of the greatest examples of adaptive radiation, I had other plans in mind involving some of their distant cousins: tropidurine lizards! The results of this study are already published (Toyama, 2017) and I will describe a bit of what I found.

Tropidurinae is a group of lizards whose representatives have diversified across South America. They come in different shapes, colors and sizes, as you would expect from any group of organisms spreading in a diverse territory in terms of habitats, climates and altitudes. Rainforests, deserts, mountains and dry forests are just some examples of the different ecosystems where you can find these lizards. Given this scenario, I wondered if the morphological diversity observed in this clade could be linked to the challenges imposed by the different habitats types found in the continent.

Inspired by similar studies that focused on other lizard radiations, I took measurements of functional morphological traits of several species of lizards coming from 10 out of the 12 genera comprising the Tropidurinae. These traits would allow me to look for a possible correspondence between morphology and habitat.

However, as I was not only interested in the link between morphology and habitat use, but also in the morphological diversity itself, I started looking at purely morphological information. The next figure shows the illustrative results of a Principal Component Analysis (PCA), which tries to separate the species as much as possible based on the morphological measurements. In the figure, we can observe how the dots of each color (representing species of the same genus) occupy a particular zone in the graph. This means that, in general, species of the same genus are, as expected, morphologically more similar between them than to species of other genera (exceptions aside, given the overlaps between some genera).

figure2

Scatter plot showing the morphological space defined by PC1 and PC2. Each dot represents the average values for a species, and species are grouped in genera (colors). Abbreviations are shown for some traits as HL (head length), HW (head width), HH (head height), BW (body width), BH (body height), Dist (distance between limbs), Htoe (longest toe of the hind limb), and Ftoe (longest toe of the forelimb).

Going a bit farther in respect to morphological diversity, Continue reading The Evolution Of Morphological Diversity In Tropidurine Lizards: the Influence Of Habitat

What Drives Substrate Use Patterns in Semiaquatic Anoles?

Anolis oxylophus at La Selva Biological Station (left, photo by Christian Perez) and Anolis aquaticus at Las Cruces Biological Station (right, posed).

Anolis oxylophus at La Selva Biological Station (left, photo by Christian Perez) and Anolis aquaticus at Las Cruces Biological Station (right, posed).

Among anoles, West Indian ecomorphs are the best known microhabitat specialists, but they are not the only ones. Semiaquatic anoles, of which there are 11 described species, live exclusively near streams and will sometimes enter water to feed or to escape a threat. The Central American species Anolis aquaticus appears to be specialized for climbing on rocks, particularly relative to other Central American semiaquatic anoles (Muñoz et al. 2015). Recent posts on A. aquaticus have addressed sleep site fidelity, dewlaps and trait scaling, and underwater foraging.

During a field ecology course with the Organization for Tropical Studies last winter, I compared patterns of substrate use between A. aquaticus and another Central American semiaquatic anole, Anolis oxylophus. Unlike A. aquaticus, A. oxylophus perches predominantly on woody and leafy substrates (Table 1). I wondered what was driving the differences in substrate use between these two species that appear broadly similar in morphology and lifestyle. Some Caribbean anoles alter their behavior to use only a narrow subset of available substrates in their habitat, whereas others have a greater breadth of substrate use that more closely reflects habitat-wide availability (Irschick and Losos, 1999; Mattingly and Jayne, 2004; Johnson et al., 2006). To evaluate whether substrate use differences between A. aquaticus and A. oxylophus are driven by substrate availability, species-specific selectivity, or both, I simultaneously quantified lizard substrate use and substrate availability within their streamside habitats.

Continue reading What Drives Substrate Use Patterns in Semiaquatic Anoles?

Legendary Brazilian Anoles Rediscovered

Several anole species are known from a single remote locality or only a few individuals, sometimes collected long ago. Because sampling these species is hard, we have a limited understanding about their biology and evolution. In a recent paper, we report on the rediscovery of Anolis nasofrontalis and Anolis pseudotigrinus, two mainland species from the Brazilian Atlantic Forest that were not reported for more than 40 years. Based on DNA sequence data, we examine their placement in the Anolis tree of life and estimate divergence times from their closest relatives. Moreover, based on the morphological attributes of newly and previously collected specimens (some of which were overlooked due to misidentification), we provide much needed taxonomic re-descriptions.

Fig. 1. Coloration in life of Anolis nasofrontalis (A, B) and A. pseudotigrinus (C, D). In A, inset shows the black throat lining of A. nasofrontalis, an uncommon trait that may be indicative of close relationships with Andean anoles (such as A. williamsmittermeierorum). Photographed specimens are females.

Coloration in life of Anolis nasofrontalis (A, B) and A. pseudotigrinus (C, D). In A, inset shows the black throat lining of A. nasofrontalis. Photographed specimens are females.

This study starts with efforts by collaborator Dr. Miguel T. Rodrigues (Universidade de São Paulo) to investigate reptiles and amphibians that have been undetected for years – a gap that could indicate human-driven extinctions. On late 2014, Dr. Rodrigues and his students (including co-author Mauro Teixeira Jr.) launched an expedition to the mountains of Santa Teresa (state of Espírito Santo, Brazil), the type locality of both A. nasofrontalis and A. pseudotigrinus. After a few days (and nights) of search, the team spotted the first A. pseudotigrinus in decades. The adult female was found sleeping on a narrow branch, (probably) unaware of its significance for South American biogeography (so were we). No signs, however, of A. nasofrontalis.

Shortly after, PhD students Paulo R. Melo-Sampaio (Museu Nacional) and Leandro O. Drummond (Universidade Federal do Rio de Janeiro) decided to visit Santa Teresa, inspired by conversations with Dr. Rodrigues. At this point, Dr. Rodrigues, my supervisor Dr. Ana C. Carnaval (City University of New York), and I had agreed that a phylogenetic study of A. pseudotigrinus would fit my PhD research well. Then, on early 2016, we got an unexpected email from Paulo and Leandro, with the first picture ever taken of an A. nasofrontalis in life. Both legendary anoles were real!

Back to the lab, we generated DNA sequence data and performed phylogenetic analyses, with completely unexpected results. First, A. nasofrontalis and A. pseudotigrinus are not closely related to the other (confirmed) Atlantic Forest species (A. fuscoauratus, A. ortonii, and A. punctatus); instead, they are close relatives of a species from western Amazonia, the “odd anole” Anolis dissimilis. These three species were found to compose a clade with A. calimae from the western cordillera of the Colombian Andes, A. neblininus from a Guiana Shield tepui on the Brazil-Venezuela border, and two undescribed Andean species (Anolis sp. R and Anolis sp. W from Poe et al. 2015 Copeia). This clade falls outside of the five major clades previously recovered within the Dactyloa radiation of Anolis, which have been referred to as species series (aequatorialis, heterodermus, latifrons, punctatus, roquet). Based on these results, we define the neblininus species series of Anolis.

Fig. 2. Phylogenetic relationships and divergence times between species in the Dactyloa clade of Anolis inferred using BEAST. Asterisks denote posterior probabilities > 0.95.

Phylogenetic relationships and divergence times between species in the Dactyloa clade of Anolis inferred using BEAST. Asterisks denote posterior probabilities > 0.95.

The neblininus series is composed of narrowly-distributed species that occur in mid-elevation sites (or adjacent habitats in the case of A. dissimilis) separated by large geographic distances. This pattern suggests a complex biogeographic history involving former patches of suitable habitat between regions, followed by habitat retraction and extinction in the intervening areas. In the case of A. nasofrontalis and A. pseudotigrinus, for instance, past forest corridors may explain a close relationship with the western Amazonian A. dissimilis. Atlantic and Amazonian rainforests are presently separated by open savannas and shrublands, yet geochemical records suggest that former pulses of increased precipitation and wet forest expansion have favored intermittent connections between them. These connections may have also been favored by major landscape shifts as a result of Andean orogeny, such as the establishment of the Chapare buttress, a land bridge that connected the central Andes to the western edge of the Brazilian Shield during the Miocene.

Fig. 3. Geographic distribution of confirmed and purported members of the neblininus species series. The inset presents a schematic map of South America around 10-12 mya, when the ancestor of A. nasofrontalis and A. pseudotigrinus diverged from its sister, the western Amazonian A. dissimilis. The approximate locality of the Chapare buttress, a land bridge that connected the central Andes to the western edge of the Brazilian Shield, is indicated.

Geographic distribution of confirmed and purported members of the neblininus species series. The inset presents a schematic map of South America around 10-12 mya, when the ancestor of A. nasofrontalis and A. pseudotigrinus diverged from its sister, the western Amazonian A. dissimilis. The approximate locality of the Chapare buttress, a land bridge that connected the central Andes to the western edge of the Brazilian Shield, is indicated.

During our morphological examinations of A. nasofrontalis and A. pseudotigrinus, it became apparent that these two species are not very different from Caribbean twig anoles, with whom they share short limbs and cryptic coloration. We learned that these features are also present in other, distantly-related mainland anoles, such as A. euskalerriari, A. orcesi, A. proboscis, and A. tigrinus. Phylogenetic relationships support that a twig anole-like phenotype was acquired (or lost) independently within Dactyloa, perhaps as a result of adaptive convergence. Alternatively, this pattern may reflect the conservation of an ancestral phenotype. In the former case, an apparent association with South American mountains is intriguing.

Unfortunately, natural history data from A. nasofrontalis and A. pseudotigrinus are lacking. It is currently unclear whether they  exhibit the typical ecological and behavioral traits that characterize the Caribbean twig anole ecomorph, such as active foraging, slow movements, infrequent running or jumping, and preference for narrow perching surfaces.

Fig. 4. Anolis dissimilis, the 'odd anole'.

Anolis dissimilis, the ‘odd anole’.

It has become increasingly clear that broader sampling of genetic variation is key to advance studies of mainland anole taxonomy and evolution. This significant challenge also provides exciting opportunities for complementary sampling efforts, exchange of information, and new collaborations between research groups working in different South American countries.

To learn more:

Prates I, Melo-Sampaio PR, Drummond LO, Teixeira Jr M, Rodrigues MT, Carnaval AC. 2017. Biogeographic links between southern Atlantic Forest and western South America: rediscovery, re-description, and phylogenetic relationships of two rare montane anole lizards from Brazil. Molecular Phylogenetics and Evolution, available online 11 May 2017.

Sex Ratios and Sexual Selection in Anolis lizards

The adult sex ratio is an important characteristic of a population, influencing the number of available mates in an area, the strength of sexual selection, and the evolution of mating systems. In our new paper in the Journal of Zoology, Michele Johnson and I use anoles to look at variation in sex ratios within and across species within a clade.

Photo by Michele A. Johnson

Photo by Michele A. Johnson

This paper had its roots when Jonathan Losos put me in touch with Michele in my first semester of grad school. Michele had compiled a massive database of detailed behavioral observations for Anolis populations and species across the Greater Antilles during her PhD on territoriality and habitat use (see Johnson et al. 2010 for more details!). While still trying to familiarize myself with the data set, I came across papers by Bob Trivers on sexual selection in anoles and his publication on the name-sake Trivers-Willard hypothesis; the combination of these topics made me curious about sex ratios and their role in sexual selection. I decided to quickly calculate the sex ratios of our localities, and given their distribution, realized that we should definitely look into this more.

<!–more–>

Sex ratios are generally very hard to measure in the field. You need to be certain that you haven’t had any biased sampling, or in other words, that you’ve made a fair attempt at censusing the population. This is quite difficult during short sampling periods! However, Michele conducted extended behavioral observations, and carefully tagged and monitored every individual in large habitat areas for ~3 weeks in each locality. This meant that we could be fairly confident that she had captured every individual in the population during her sampling periods, and her total counts of male and females in the population would be accurate. Even more, she had these adult sex ratios for 14 species, with some of those species being sampled at multiple localities. Given these data, we could actually both look at sex ratios across the Anolis clade, and within multiple anole species, for the first time.

We had two main questions: 1) were the sex ratios of these anole populations significantly skewed (i.e., were they very far off  from a 50:50 male-to-female ratio?) and 2) did the adult sex ratio of a population correlate with the strength of sexual selection in that population? For question 2, we used two measurements of sexual size dimorphism as a proxy for the strength of sexual selection. Sexual selection generally drives an increase in sexual size dimorphism (i.e., the difference between males and females in body size), but is also thought to be related to sex ratio skew (as the more skewed a population sex ratio, the more competition for mates or mating opportunities). We predicted that species with more skewed sex ratios would show an increase in sexual size dimorphism. Given that ecomorphs are an important component of evolution in anoles, and are commonly associated with varying levels of sexual size dimorphism, we also decided to test for a correlation between sex ratio skew and ecomorph type.

We found that sex ratios varied widely across and within anoles, ranging from a very female biased 0.32 in Anolis krugi to a male biased 0.61 in Anolis smaragdinus (sex ratios are expressed as the total number of adult males divided by the total number of both adult males and females in the population). Adult sex ratios also varied between different localities within a species (we had six species with multiple localities). We found two populations with significantly skewed sex ratios (Anolis krugi and Anolis valencienni) but based on Fisher’s test of combined probabilities, the sex ratios of anoles overall are not skewed away from 50:50.

I should note, however, that it is intrinsically extremely difficult to detect a skewed sex ratio in a natural population. We’re trying to measure deviations from a 50:50 sex ratio, and this requires surprisingly high population sizes since the binomial distribution has a broad center. For instance, to detect a true underlying sex ratio of 0.4 or 0.6 (away from our null of 0.5), we would need population sizes of >780 lizards to detect a significant skew 80% of the time. This is just an illustration, but the main point is that these population sizes might not exist for a given species – and so detecting significantly skewed sex ratios might not be possible at all. This is especially difficult when looking at small or endangered populations – there sex ratio skew might be a big problem, but impossible to demonstrate statistically. The general takeaway here is that sex ratio skew in a population can be biologically important, but not statistically significant.

We then used both the categorization of the anole species by sexual size dimorphism (low or high SSD) and the measured sexual size dimorphism of each population (calculated by average male SVL divided by average female SVL, minus 1). We used both of these estimates of SSD to test whether the sex ratio of a population correlated with the sexual size dimorphism of that population, as predicted by sexual selection theory. Turns out we were completely off – there was really no correlation between sex ratio skew and measured SSD, categorical SSD, or ecomorph (see figure 1, posted below,  for a visual of this lack of correlation!).

Figure 1 (from the paper) : Sex ratio versus sexual size dimorphism. Sex ratio is represented as the proportion of males among adults in the population, while sexual size dimorphism was calculated dividing the average SVL of the larger sex by the average SVL of the smaller sex, and subtracting 1 for each population. Each circle represents 1 of the 21 localities sampled in this study. The dashed line represents an equal sex ratio of 0.5. We found no relationship between sexual size dimorphism and sex ratio across the 21 localities (PGLS: adjusted R2 = −0.08, P = 0.86).

Figure 1 (from the paper) : Sex ratio versus sexual size dimorphism. Sex ratio is represented as the proportion of males among adults in the population, while sexual size dimorphism was calculated dividing the average SVL of the larger sex by the average SVL of the smaller sex, and subtracting 1 for each population. Each circle represents 1 of the 21 localities sampled in this study. The dashed line represents an equal sex ratio of 0.5. We found no relationship between sexual size dimorphism and sex ratio across the 21 localities (PGLS: adjusted R2 = −0.08, P = 0.86).

So what’s the general message here? Sexual size dimorphism does not correlate with adult sex ratios across anole species, and so the relationship between strength of sexual selection, sex ratio bias, and sexual size dimorphism may be more complicated than we initially assumed. However, anole sex ratios can range widely between species, and within populations. Given the variance within anole species, the adult sex ratio is probably a better description of a locality, or population, than an intrinsic quality of an entire species. We also think that the influence of various localized environmental factors may impact sex-specific mortality or dispersal, which in turn which cause differences between localities in adult sex ratio skew.

This is my first anole paper, and it’s really nice to see all the brainstorming and discussions put into print. It was also great to get to know and work with Michele, and learn more about her research and behavioral work in anoles (we even got to meet in person at the Evolution conference last year!). This paper was also my first small step into the world of sex ratio and sex determination theory which now forms a large part of my PhD work, so I’m very grateful for the introduction to the subject. Anyway, feel free to email us with any questions and we hope you enjoy the paper!

Paper here: Sexual selection and sex ratios in Anolis lizards

 

City Lizards Are Hesitant Feeders

cristatellus.pole

Figure 1. Anolis cristatellus male in survey position.

Foraging behavior reflects a trade-off between the benefits of obtaining vital resources and the potential costs of energy expenditure, missed mating opportunities, and predation. Through time, selection should canalize foraging behaviors that optimize fitness within a given environment, but novel habitats, like urban landscapes, may require behavior to change. For example, human-landscape modification often results in significant reductions in structural complexity of habitat as compared to natural areas, potentially leaving individuals with a greater sense of perceived vulnerability as they venture out to feed. Moreover, these landscapes can alter the diversity and density of predators in ways that might leave prey with a greater sense of perceived predation risk.

In a recent paper in Urban Ecosystems, Chejanovski et al (2017) sought to quantify differences in foraging behavior between anoles from urban areas and those from more natural, forested locations. They utilized two trunk-ground anoles: Anolis sagrei in Florida and A. cristatellus in Puerto Rico. In both urban and natural habitats, they located male lizards in survey posture (Fig 1), which indicates an individual is likely searching for food, and placed a tray with mealworms on the ground at a fixed distance from the perch. They measured each lizard’s latency to feed which was the time it took to the lizard to descend from its perch and capture a mealworm.

Because the availability of complex habitat structure and the proximity of predators might both influence foraging behavior, they experimentally manipulated perch availability for A. sagrei and predator presence for A. cristatellus in both urban and natural habitats. For A. sagrei, they provided half the individuals with two extra perches between the lizard’s original position and the food tray. For A. cristatellus, they manipulated perceived predation risk by placing a static bird model on the opposite side of the feeding tray from half the lizards.

Additionally, they measured several other factors that might influence foraging behavior: the number of available perches within a fixed radius of each lizard – increased habitat complexity might result in lower perceived predation risk; perch height of each individual – those that perch lower to the ground may be more motivated to feed and those that perch higher may be satiated; estimates of body temperature by placing a copper model at the original position of each lizard – body temperature can influence locomotor function and this may have consequences for how easily a lizard can escape predation and play a role in its perceived risk. They also measured the density of conspecifics in the immediate vicinity and noted when conspecific individuals captured mealworms from the feeding tray.

Finally, they measured SVL and mass for a representative sample of each population (urban and natural) in order to calculate body condition. Trade-offs between costs and benefits of foraging decisions can be influenced by satiation of hunger, and body condition, which increases with food consumption, may indicate the extent to which individuals are well-fed.

For both species, lizards from urban areas had a longer latency to feed and demonstrated lower overall response rates to food trays; many individuals never attempted to capture a mealworm in the allotted time (20 minutes). For A. sagrei, habitat (urban vs. natural) best explained feeding latency, but perch height and the presence of conspecifics were also important determinants of feeding latency for A. cristatellus. Individuals perching lower had shorter latency, and latency was shorter when a conspecific attempted to feed from the tray. Neither experimental perch availability nor perceived predation risk (bird model) had any influence on foraging behavior. In both species, individuals from the forest were smaller (SVL) and less massive than those from the city. Body condition was higher for urban A. sagrei but did not differ between natural and urban habitats for A. cristatellus.  

Capture

Differences in foraging behavior for male A. cristatellus between natural and urban habitats.

Because of the reduced availability of perches and structural complexity in urban habitats, urban lizards could have generally higher perceived predation risk and this might explain their reluctance to feed; however, experimental perch availability did not influence foraging behavior for A. sagrei and an artificial predator had no effect on A. cristatellis. The latter may simply reflect that the experimental predator was stationary and a moving predator may have elicited different results.

It is possible that foraging differences reflect food availability in urban vs natural habitats, and thus motivation to forage. Urban anoles had higher body condition and may be generally better fed than those from the forest; however, the authors found no significant correlation between individual body condition and latency to feed. It is also possible that mealworms represent a novel food source for urban anoles, and this resulted in a hesitance to initiate feeding since many animals are reluctant to approach novel objects/ food (neophobia).

In summary, this study demonstrates that differences do exist in foraging behavior for two distantly related species of anoles between urban and forested habitats. The increased latency to feed observed in urban anoles could be due to perceived predation risk, foraging motivation, neophobia, or some combination. What is left to be determined is the extent to which these behavioral differences might be adaptive in their respective habitats.

Of Rats and Reptiles: An Expedition to Redonda

IMG_4456

Anolis nubilus male and female from The Anoles of the Lesser Antilles.

In 1972, James “Skip” Lazell published a monograph on the Anoles of the Lesser Antilles including the species description of Anolis nubilus, an endemic anole restricted to the island of Redonda. His description of the animal and island, like the rest of the monograph, is colorful and evocative:

“The tiny islet is exceedingly steep-to, and rises nearly 1000 feet out of the sea. There is virtually no surrounding bank, and the full swell of the western North Atlantic pounds Redonda’s cliffs. A tiny, nearly vertical gut on the leeward side provides the only access to the top of the islet up the cliffs; great blocks of basalt lie at the foot of this gut and one’s original entrance to Redonda is made by jumping onto these blocks as the boat goes past them. It is about like jumping from a moving elevator onto a card table, except that elevators give more notice of directional reversals… but getting on is just the beginning. …

The top of Redonda is a rolling wold and a favorite place of innumerable nesting sea birds; the gut provides a route for their guano to descend the cliffs, and it dries to a thick powder there. Because of its lee-ward location, a chimney effect is produced in the gut, and the guano dust, mixed with the volcanic sand weathered from the parent rock, tends to rise when disturbed. As one toils up the gut under the tropical sun, one is accompanied by a cloud of this dust, which soon mingles with one’s own sweat to produce a wondrously aromatic and abrasive, though rather gluey, bath. At the top, jumbles of rocks and clumps of prickly pear rise gently to the old ruins, complete with a hedge of bougainvillea and a single tree. This is the home of Anolis nubilus. …

Surely Redonda once supported more vegetation, and presumably Anolis nubilus then had an easier life. The feral goats should be extirpated on this remarkable island, whose only known nonflying vertebrates are species found nowhere else on earth.”

Now, 45 years, 1 week, and 4 days later, I’m headed to Redonda to gather baseline lizard data on exactly such a goat extirpation.

Skip did miss one nonflying vertebrate in his account; Rattus rattus has taken up residence en masse on Redonda. The black rats are so plentiful now that they’ve taken to stalking the lizards on the island in daytime—“tiger rats,” according to Dr. Jenny Daltry, one of the researchers leading the island restoration effort. And so, the government of Antigua and Barbuda, in conjunction with numerous conservation NGOs including Flora and Fauna International, has decided to remove the goats and rats from Redonda in an attempt to restore the island and help its three endemic lizard species to recover.

Redonda is home to not just A. nubilus but also a jet black ground lizard, Ameiva atrata and an as-yet unnamed dwarf gecko, Sphaerodactylus sp. Presumably, A. nubilus would be perched high in vegetation avoiding the roving A. atrata; however, after centuries of goat grazing on Redonda, that vegetation has been reduced to a single Cassuarina tree. So, while that tree is likely swarming with anoles, most of the A. nubilus are spending their time hopping around the boulders of Redonda. Normally this would put them in range of the roving ground lizards, but it sounds as though both lizards should be more worried about those hungry black rats.

Fortunately for all of Redonda’s reptiles, as of a few weeks ago the goats on the island took a one-way ferry ride to new pastures (not a euphemism) and, well, starting soon the rats will be making their way to the great big garbage heap in the sky (definitely a euphemism). My goal is to get to Redonda and gather as much baseline data on the lizards as possible to see whether and how the lizard community changes on a goat-less, rat-free Redonda.

That’s no easy task, though. Here’s a picture of Redonda:

Photo credit: Dr. Jenny Daltry

Photo credit: Dr. Jenny Daltry. I’m reasonably sure that’s the gut there, in the foreground of the image.

Believe it or not, that’s the pleasant side of the island. Here’s the other:

Photo credit: TopTenz.net

Photo credit: TopTenz.net

We decided that hauling a week’s worth of research and camping gear up Lazell’s gut (let alone jumping to that card-table basalt) was out of the question, so I’m going to be arriving by helicopter. As if the rats weren’t enough, Redonda has no source of fresh water so we’ll be carrying in food and drink for the 8 days on the island. No power either, so I’ve been putting together solar kits to try to get enough juice to run a computer and spectrophotometer.

All in all, it’s going to be an adventure! I’ll update Anole Annals when I return, but I’ll also be posting more frequent updates to my personal blog and twitter. I’d love to hear from you, especially if you have any tips for rat-proofing tents (seems more efficient to just bait the other ones, right?).

Citation: Lazell, J.D. 1972. The Anoles (Sauria, Iguanidae) of the Lesser Antilles. Bulletin of the Museum of Comparative Zoology. 143(1).

Anolis sagrei Now in the Southern Hemisphere, First Record for South America

Anolis sagrei has successfully invaded several countries including the United States, Mexico, some Caribbean islands, and even Taiwan and Singapore in Asia. As an invasive species, brown anoles can reach high population densities, expand their range rapidly, and have a negative effect on native species of lizards.

Now, this tree lizard has gone further. A group of Ecuadorian herpetologists recently discovered some individuals of this species in two localities on the Pacific coast of Ecuador. These individuals also represent the first record of this invasive species in South America.

DSC_0428

 A juvenile male individual of Anolis sagrei  found in Ecuador

23903-79180-1-SP

World map showing the distribution of Anolis sagrei. Green spots correspond to native distribution, blue spots non-native distribution, and the red star corresponds to the new records from Ecuador.

Individuals were found in an urban area with a mix of native and introduced species of plants. Although an established population has not been confirmed, this finding certainly represents a potential threat to local species of lizards from Ecuador, home to 38 species of anoles. A note reporting this discovery is in publication process.

Acknowledgments

Thanks to Omar Torres-Carvajal who helped with the post.

Cuban Anolis porcatus introduced to Brazil (perhaps through Florida?)

Several anole species have become established outside of their native ranges as a result of human-mediated transportation, being introduced to Japan, Singapore, Taiwan, Hawaii, the continental U.S., and beyond. Alien anoles can have major impacts on the ecological communities that they invade, for instance leading to local extinction of arthropod taxa and displacing native anole species. It is therefore key to detect and report instances of introduction by these potentially aggressive invaders, as well as to document their geographic spread in colonized regions. In a recent paper, we report on the presence of Anolis porcatus, a species native from Cuba, in coastal southeastern Brazil, using DNA sequence data to support species identification and examine the geographic source of introduction.

Anolis porcatus collected in Brazil, and comparison with the native anole A. punctatus. A, male A. porcatus showing green coloration. B, male A. porcatus showing brown coloration. C, the pink dewlap of male A. porcatus. D, female A. porcatus. E, male A. punctatus, a native anole species. F, the yellow dewlap of male A. punctatus. Picture credits: A–D, Mauro Teixeira Jr.; E, Renato Recoder.

Anolis porcatus collected in Brazil, and comparison with the native anole A. punctatus. A, male A. porcatus showing green coloration. B, male A. porcatus showing brown coloration. C, the pink dewlap of male A. porcatus. D, female A. porcatus. E, male A. punctatus, a native anole species. F, the yellow dewlap of male A. punctatus. Picture credits: A–D, Mauro Teixeira Jr.; E, Renato Recoder.

Perhaps embarrassingly, this study started with Facebook. On August 2015, Ricardo Samelo, an undergraduate Biology student at the Universidade Paulista in Santos, posted a few pictures of an unknown green lizard in the group ‘Herpetologia Brasileira.’ A heated debate about the animal’s identity took place, with people eventually agreeing on Anolis carolinensis. On my way to Brazil to join the Brazilian Congress of Herpetology, I contacted Ricardo (but only after properly hitting the ‘like’ button) and proposed to examine whether the exotic anole was established more broadly in the Baixada Santista region.

To our surprise, local residents knew the lizards well, with some people quite fond of the ‘lagartixas’ due to their pink dewlap displays. People could often tell when the anoles were first noticed in the vicinities – ‘six months’, ‘nine months’, ‘one year ago’ –, suggesting a rather recent presence. Guided by these informal reports, we sampled sites in the municipalities of Santos, São Vicente and Guarujá, where we found dozens of lizards occupying building walls, light posts, fences, debris, trees, shrubs, and lawn in residential yards, abandoned lots, and alongside streets and sewage canals. It was clear that the alien anoles are doing great in human-modified areas; the high density of individuals across multiple sites, as well as the presence of juveniles with various body sizes, seem to suggest a well-established reproductive population.

Sites in the Baixada Santista in southeastern coastal Brazil where introduced A. porcatus were detected. 1, Guarujá. 2, Santos. 3, São Vicente. Green indicates Atlantic Forest cover; gray indicates urban areas; black indicates water bodies.

Sites in the Baixada Santista in southeastern coastal Brazil where introduced A. porcatus were detected. 1, Guarujá. 2, Santos. 3, São Vicente. Green indicates Atlantic Forest cover; gray indicates urban areas; black indicates water bodies.

By reading and bugging experienced anole researchers about the Anolis carolinensis species group, I learned about paraphyly among species, hybridization, and unclear species diagnosis based on external morphology. As a result, my PhD supervisor, Dr. Ana Carnaval, and I decided to recruit Leyla Hernandez, by the time an undergraduate student in the Carnaval Lab at the City University of New York, to help generate DNA sequences to clarify the species identity, and perhaps track the geographic source of introduction in Brazil. To our surprise, a phylogenetic analysis found Brazilian samples to nest within Anolis porcatus, a Cuban species that has also been introduced to Florida and the Dominican Republic. Brazilian A. porcatus clustered with samples from La Habana, Matanzas, and Pinar del Río, which may suggest a western Cuban source of colonization. Nevertheless, Brazilian specimens are also closely related to a sample from Coral Gables in Florida, which may suggest that the Brazilian population originated from lizards that are exotic elsewhere.

Phylogenetic relationships of A. porcatus introduced into Brazil (indicated in red), inferred using MrBayes based on a mitochondrial DNA locus. Purple indicates samples of A. porcatus invasive elsewhere (Florida and the Dominican Republic). Blue indicates native Atlantic Forest anole species. Asterisks indicate posterior probability >0.95. Picture depicts a male A. porcatus collected in São Vicente, Brazil.

Phylogenetic relationships of A. porcatus introduced into Brazil (indicated in red), inferred using MrBayes based on a mitochondrial DNA locus. Purple indicates samples of A. porcatus invasive elsewhere (Florida and the Dominican Republic). Blue indicates native Atlantic Forest anole species. Asterisks indicate posterior probability >0.95. Picture depicts a male A. porcatus collected in São Vicente, Brazil.

The presence of A. porcatus in the Baixada Santista may be related to the country’s largest seaport complex, the Porto de Santos, in this region. Numerous storage lots for intermodal shipping containers were situated near sites where the lizards were detected, and in one instance we found the animals sheltered inside an open container. An exotic green anole (identified as A. carolinensis) was previously found in Salvador in Brazil’s northeast; like Santos, Salvador hosts a major seaport complex, which may indicate that the exotic anoles reached Brazil after being unintentionally transported by ships bringing goods from overseas perhaps twice independently.

It is currently unclear whether A. porcatus will be able to expand into the surrounding coastal Atlantic Rainforest, or into more open natural settings such as shrublands in the Cerrado domain. It is also unknown whether this species will have negative impacts on the local ecological communities. In Brazil, introduced A. porcatus may potentially compete with other diurnal arboreal lizards, such as Enyalius, Polychrus, Urostrophus, and the native Anolis. Five native anoles inhabit the Atlantic Forest (for sure): A. fuscoauratus, A. nasofrontalis, A. ortonii, A. pseudotigrinus, and A. punctatus. While none of them is currently known to occur in sympatry with A. porcatus, the worryingly similar A. punctatus has been reported for a site in Bertioga located only 50 kilometers from the site in Guarujá where we found the exotic anoles.

To properly evaluate the potentially invasive status of A. porcatus in Brazil, we hope to continue assessing the extent of its distribution and potential for future spread, as well as to gather data about whether and how A. porcatus will interact with the local species – especially native Brazilian anoles. This seemingly recent, currently expanding colonization also represents an exciting opportunity for comparisons with other instances of introduction of A. porcatus, as well as the closely-related A. carolinensis, based on ecological and phenotypic data.

Studying such mysterious alien anoles in Brazil was made much more tractable through advice from Jonathan Losos and Richard Glor. Thank you!

To learn more: Prates I., Hernandez L., Samelo R.R., Carnaval, A.C. (2016). Molecular identification and geographic origin of an exotic anole lizard introduced to Brazil, with remarks on its natural history. South American Journal of Herpetology, 11(3): 220-227.

Habitat Disturbance Negatively Affects the Body Condition Index of Anolis antonii

Anolis antonii

Anolis antonii from the agricultural area

Habitat disturbance is considered one of the most important threats to biodiversity. Particularly, anthropogenic disturbance for agricultural practices alters the original structure of Anolis habitats and consequently negatively affects their health and survival. Because the body condition index (BCI) is an effective indicator to assess the health of animals, we hypothesized that the BCI of the Colombian endemic lizard Anolis antonii from an undisturbed habitat (natural area) would be higher than that from the disturbed habitat (agricultural area).

We studied two populations of Anolis antonii from the municipality of Ibague, Tolima, Colombia: (1) a population from an agricultural area cultivated with coffee (Coffea arabica) and plantains (Musa paradisiaca), and (2) a population from a secondary forest, an anthropogenic-free area. We measured the snout-vent length (SVL) and body mass (BM) of adult anoles (males and females)and calculated BCI from the residuals of a linear regression between BM and SVL.

Fig 2. A) Forest habitat and B) Agricultural habitat of Anolis antonii (Ibagué – Colombia)

We found that the BCI of the lizard population from the agricultural area was significantly lower than that of the secondary forest population. Consequently, A. antonii from the secondary forest, with a higher BCI, might have a greater ability to compete for available resources and survive than those from the cultivated area. Thus, this work shows that anthropogenic disturbance negatively decreases the body conditions of A. antonii lizards, which might represent a forthcoming threat for its conservation, especially due to the current habitat deterioration of this species by agriculture activities.

Read the paper:

Gallego-Carmona, C.A., Castro-Arango, J.A. and Bernal-Bautista, M.H., 2016. Effect of Habitat Disturbance on the Body Condition Index of the Colombian Endemic Lizard Anolis antonii (Squamata: Dactyloidae). South American Journal of Herpetology 11(3):183-187.

Adult Male Density Influences Juvenile Microhabitat Use in Brown Anoles

Photographs of the housing conditions used in the experiment. (a) One of the experimental enclosures (with an artificial tree) surrounded by blinds on all sides (note, the front blind was pulled back to reveal the tree and cage). (b) Close-up of the available horizontal perches. (c) Juvenile Anolis sagrei with its identification number on the lateral body surface for visual identification.

Fig 1. Photographs of the housing conditions used in the experiment. (a) One of the experimental enclosures (with an artificial tree) surrounded by blinds on all sides (note, the front blind was pulled back to reveal the tree and cage). (b) Close-up of the available horizontal perches. (c) Juvenile Anolis sagrei with its identification number on the lateral body surface for visual identification.

For many animals, optimal habitats vary across age classes, and individuals shift habitat use as they age. While many studies have documented such age-specific habitat use, most are observational and do not identify the causal factors. In addition, we know that competition between species has been an important driver of habitat use in Anolis lizards. However, less is known about the role of competition on habitat use within species of anoles, especially between age classes.

Dan Warner and I previously found that adults use higher and thicker perches than juveniles at our field site in northeastern Florida (Delaney and Warner 2016). We hypothesized that this variation was a result of adults forcing juveniles to suboptimal habitat. Thus, we altered the density of adult males in mesh enclosures (Fig. 1) in the lab and monitored changes in juvenile microhabitat choice.

Continue reading Adult Male Density Influences Juvenile Microhabitat Use in Brown Anoles

Anoles Are Habitat Specialists at the Individual Level Too

Anoles are probably best known for the ecomorph story: the presence of specialized species adapted to the same sets of structural microhabitats on different islands. Anoles in the Greater Antilles have contributed hugely to our understanding of both the evolutionary history and the contemporary ecology of communities of specialists.

While they are better known for specialization of species in communities, anoles have also contributed to our understanding of within-species ecological diversity. Around the same time that Ernest Williams was developing the ecomorph concept, Roughgarden (1972) used data from Lesser Antillean anoles to introduce a new framework for investigating the extent to which a population’s niche width (i.e. the diversity of habitats it uses or prey it eats) is determined by variation among individuals versus variation within individuals. For example, individuals in a population of Anolis roquet differ in the size of prey they consume, mainly because larger individuals can catch and ingest larger prey items. While Roughgarden’s early work set the stage for an explosion of studies of individual specialization over the past decade or two (reviewed in Araújo et al. 2011), surprisingly little work has been done to revisit individual specialization within species of anoles. In particular, we don’t know enough about how much individuals specialize in important aspects of microhabitat that differentiate ecomorphs, especially perch height and perch diameter.

"Gar" lived alone on my desk, so I don’t know if he was an individual specialist or not

“Gar” lived alone on my desk, so I don’t know if he was an individual specialist or not

Anole Annals contributors Ambika Kamath and Jonathan Losos have helped to fill this gap with a study just published online in Evolution. Ambika and her team spent a summer observing microhabitat use of a population of brown anoles (Anolis sagrei) in a forested park in Gainesville FL. They marked lizards with colored beads, and repeatedly recorded individual lizards’ perch height and diameter, compiling a total of over 1000 observations of 80 anoles. They grouped perch heights and perch diameters into classes, then compared the distribution used by each individual to the distribution used by the whole population (or to the distribution available to that individual) using a proportional similarity index. The mean value of this index gives a measure of the overall degree of individual specialization in a population, as lower overlap values tell us that individuals are specializing on a subset of the available perches.
Continue reading Anoles Are Habitat Specialists at the Individual Level Too

SICB 2017: Are Anoles Less Stable When Running Without Using Claws?

Photo courtesy of Catalina Mantilla

Photo courtesy of Catalina Mantilla

This post was written by Brittney Ivanov, research technician in Michele Johnson’s lab at Trinity University.

Catalina Mantilla, a Ph.D. candidate at Florida International University working with Tonia Hsieh of Temple University, is interested in how anoles use their toepads and claws when they run. For most animals, movement on vertical perches such as tree trunks or buildings usually requires specialized morphologies to adhere to these substrates. While many species have evolved adaptations for moving through complex arboreal habits (e.g., prehensile tails or feet, sticky pads, spines), anoles evolved enlarged toepads and distinct claws, presumably to allow for better adhesion. The morphologies of these specialized structures can greatly impact performance; for example, greater toepad area is associated with greater clinging ability. Catalina wanted to better understand how toepads and claws work together to enhance running performance.

Catalina collected 17 males from four Anolis species (A. carolinensis, A. sagrei, A. cristatellus, and A. distichus). Each male was tested in four different running courses to test performance at difference inclines and on different substrates. Two of the courses were positioned at a 45° incline and two at a flat (0°) incline. Plexiglass covered one course at each incline to allow the use of toepads and eliminate the use of claws. Nylon mesh covered the other course at each incline to test the use of both toepads and claws. Performance was evaluated using mean relative sprint speed, relative stride length, and stride frequency.

Catalina found, unexpectedly, that when the lizards ran on the level plexiglass, they ran slower, took shorter strides, and increased their stride frequency compared to when they ran on the inclines. These results suggest that anoles are less stable when they can’t use their claws! in addition, these data support the idea that the combination of toepads and claws is important for their running performance. In the future, Catalina hopes to increase the number of species in this study to determine the effect of ecomorph on claw and toepad interactions during running, and to evaluate limb function changes when running across different inclines.

SICB 2017: How Anoles Climb Trees: Ecomorph Differences in Neuromuscular Function

Kathleen Foster presents her work to a packed room at SICB.

Kathleen Foster presents her work to a packed room at SICB.

Regular readers of AA will be familiar with the differences in microhabitat use that define the Anolis ecomorphs, but do species with such distinct structural habitats move differently on their specialized perches? In other words, does muscle function differ between the ecomorphs? In the very last session at this year’s SICB, Kathleen Foster, currently a postdoctoral researcher at the University of Ottawa studying the biomechanics of fish locomotion (come back to anoles, Kathleen!), presented a portion of her graduate work in Tim Higham’s lab at the University of California, Riverside, to address this question. She used high speed video to film five species of anoles running on broad and narrow perches at two angled inclines, combined with electromyography to record fore- and hindlimb muscle activity during running.

Photo courtesy of Kathleen Foster.

Photo courtesy of Kathleen Foster.

Kathleen found that all five species had greater motor unit recruitment on steeper inclines than on horizontal perches, and that muscle activity is shorter but begins more abruptly on inclines. Further, recruitment of the gastrocnemius (a “calf” muscle) was greater on broad perches, because the way lizards sit on narrow perches limits the function of this muscle. If you’ve seen how anoles position their feet on both sides of narrow perches, it’s easy to understand how this posture prevents effective propulsion by ankle extension. Kathleen also found several intriguing differences that distinguish trunk-ground species’ muscle function from trunk-crown and crown-giant species. The activity of the caudofemoralis (a limb retractor muscle in the hindlimb) changes more in trunk-ground species as a function of incline, and trunk-ground species use the biceps and gastrocnemius more in the early stance phase of propulsion than trunk-crown species.

Overall, these data help us understand how specialization in neuromuscular function can allow different anole species to successfully move through their varying habitats, and offer insight into how behavioral differences depend on the muscles that underlie them.

SICB 2017: Impacts of Urbanization on Morphology, Thermal Preference, and Parasitism

Chris Thawley at a crossroads.

Chris Thawley at a crossroads.

Urban environments are widespread and expanding across much of the earth, and this urbanization likely affects the flora and fauna in its path. Anoles are no exception and are frequently observed perching on anthropogenic structures. Thus, Chris Thawley, a post-doc in Jason Kolbe’s lab at the University of Rhode Island, and colleagues wondered how the abiotic and biotic changes in urban areas influence anole traits.

Thawley compared populations in urban and natural habitats of two species that we’re quite familiar with on Anole Annals – the Brown Anole (Anolis sagrei) and the Puerto Rican Crested Anole (Anolis cristatellus). Thawley found that A. sagrei prefers warmer temperatures than A. cristatellus, but that urban anoles do not differ in thermal preference than natural anoles for either species. Alternatively, urban male A. cristatellus and both sexes of urban A. sagrei were larger than their natural counterparts. As for parasites, A. sagrei had a higher parasite prevalence than A. cristatellus, but urban anoles did not differ from natural anoles in either species in parasite prevalence. However, for the A. sagrei that were parasitized, urban A. sagrei had higher parasite loads than natural A. sagrei.

These findings show that urbanization can influence anole morphology and parasite ecology. Thawley has just begun this work, and I look forward to seeing his future research on anole adaptation to urban environments!

SICB 2017: A Field Based Approach to Study Behavioral Flexibility

storks-poster-sicb-2017

Levi Storks explains his project in New Orleans.

Most animal learning studies have been conducted in the lab with the assumption that those findings are representative of behavior in the field. However, assessing behavior in the field increases ecological relevance. In addition, birds and mammals have received much of the attention in cognitive studies. Yet we on Anole Annals know that these lizards can be quite clever.

Levi Storks, a Ph.D. student in Manuel Leal’s lab at Mizzou, set out to address these issues by designing a method for testing behavioral flexibility in brown anoles (Anolis sagrei). Wild lizards in the Bahamas were allowed to feed unrestricted on a maggot placed in the middle of a testing apparatus in order to acclimate lizards to the structure. Storks then used a clear plastic tube to block the direct route to food, requiring lizards to move to either end to gain access. Lizards that successfully completed this task were then tested to see if they could associate unique patterns on the ends of the tube with single openings.

Storks found that a subset of lizards could successfully complete the first detour task, and lizards made fewer errors over the course of solving the detour task. These findings suggest brown anoles can learn and exhibit behavioral flexibility. Stay tuned for more of Levi’s work as he’ll be applying these methods to assess differences in behavioral flexibility between populations that vary in ecology!   

 

SICB 2017: Muscle Physiology and Social Behavior

Above: Faith Deckard presenting her research on how muscle physiology may explain variation in social behavior among Caribbean anoles.

Above: Faith Deckard presenting her research on how muscle physiology may explain variation in social behavior among Caribbean anoles.

Marathon runners and elite sprinters, like Usain Bolt, have dramatic differences in their muscle physiology that allow them to specialize in their respective track-and-field events. Whereas sprinters have lots of muscle fibers that produce high force but fatigue quickly, marathon runners have lots of muscle fibers that produce less force but allow much longer activity because of their reliance on aerobic respiration. Might this be true for our beloved Caribbean anoles, too? Faith Deckard of Michele Johnson’s lab at Trinity University tried to answer that very question. She studied six species of anoles in the Dominican Republic to test whether anoles that have higher rates of dewlap extension and extend their dewlap for a longer duration have dewlap muscles with a higher proportion of slow-twitch muscle fibers that can be used for endurance. Surprisingly there was no significant correlation between the two behavioral traits and the proportion of slow-twitch fibers! However, this scrutinizing attendee feels pretty strongly that there is a relationship that is just yet to be teased apart statistically. The raw data Faith presented looked very convincing to me, so we’ll see what the future holds for this question. Faith’s results are a very interesting clue to the still-elusive mechanisms that underlie anole behavioral diversity.

SICB 2017: Leptin as a Mediator of Trade-offs

Above: Andrew Wang presenting his research on how leptin may be a mechanism underlying life-history trade-offs in green anoles.

Above: Andrew Wang presenting his research on how leptin may be a mechanism underlying life-history trade-offs in green anoles.

All of the gumbo, Po boys, and beignets consumed by attendees of SICB 2017 have to go somewhere after consumption. Much of the energy contained in those delicious foods is used for very important maintenance functions in your body: metabolism, cell repair and replacement, and your immune system. What’s left over after maintenance costs can then be divided amongst other tasks, such as reproduction, movement, and wide variety of other tasks. Unlike humans, anoles do not have unlimited access to gigantic portions of gumbo, so their energetic investments require much harder decisions. Once energy from a cricket, for example, has been put into the immune system, it can no longer be used for making eggs or patrolling a territory a little bit longer. Andrew Wang of Jerry Husak’s lab at the University of St. Thomas was interested in what mechanisms are involved with anoles making these investment “decisions.” He did this by forcing allocation of resources to an energetically expensive trait (endurance running) by exercise training lizards to see what would happen to everything else that they might invest in.

Previous work showed that exercise training and diet restriction results in dramatic trade-offs with reproduction and the immune system. He suspected that what might explain this suppression was the hormone leptin, which is made by fat cells (yours make it, too). Since bigger fat cells means more leptin in the body, leptin can be thought of as a signal to the brain and body of how much resources are available for investment. Indeed, without sufficient leptin, reproduction grinds to a halt from the brain downward. Much like elite athletes, Andrew’s marathon lizards have little to no fat stores in their body, thus suggesting a role for leptin. To address this question, he supplemented half of the lizards with leptin (the rest got only saline as a control) to see if he could “rescue” immune function and reproduction. Interestingly, he found that leptin did rescue his measure of immunity, but it did not rescue reproduction. He attributes this latter finding to either (1) a lack of energetic resources to produce eggs even if there is a leptin signal or (2) the stress of the leptin injections over-rode the leptin signal in the brain where reproduction is controlled. His results suggest some very complex interactions in physiological pathways that can result in the trade-offs observed in many animal species.

Leptin is best known as a satiety hormone, but it has important roles as a signal to the body of adequate energy stores. Image from wiki.brown.edu.

SICB 2017: Sex-Specific Predictors of Performance

Green anole image from reptilesmagazine.com.

What does it take be a good sprinter? How about a marathon runner? One might think that the traits responsible for such performance traits would be the same in males and females. If you are a green anole, that just isn’t true. Annie Cespedes, working in Simon Lailvaux’s lab at the University of New Orleans, explored the multivariate predictors of seven performance traits (sprint speed, bite force, cling force, exertion, endurance, jump power, and climbing power) in male and female green anoles. Annie explained how animals in nature rely on lots of different performance traits in their daily lives, and the large difference in body size and shape between male and female anoles might mean that the two sexes use different means to be successful in life. To add to this complexity, some individuals are just better overall at ALL performance traits than others (imagine a couch potato versus a very fit athlete), and one must account for this to understand what shapes anole performance.

Multivariate statistics allowed Annie to show that males and females do indeed differ in performance, but only in clinging ability, sprint speed, bite force, and jump power. Even more interesting, the suites of morphlogical traits that explained performance ability differed substantially between the sexes. For example, small females with large leg muscles were better sprinters and jumpers than females who are smaller and are better biters and endurance runners. What is especially important about Annie’s research is her approach. When considering how animals evolve, one must do so by simultaneously looking at a multitude of traits that might impact their survival and reproduction. By knowing how morphology predicts performance, we can begin to better understand how evolution will shape that morphology when selection acts on those performance traits.