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The Lonely Clouded Anole on a Pacific Island

Anolis nebulosus

Anolis nebulosus. Photo by Hugo Siliceo-Cantero.

By H. Hugo Siliceo-Cantero and A. Garcia

In the late 1980´s, the scientists Bradford C. Lister and Andrés García discovered an interesting population of clouded anoles inhabiting the small 3.3 ha island of San Agustin located just off the Pacific coast of Jalisco, Mexico. This island was also close to the actual protected area of tropical dry forest on the mainland in the Chamela-Cuixmala Biosphere Reserve. Lister and García reported that the abundant anole population on San Agustin was maintained a decade later at much higher densities than the mainland population. We began to study this population in 2007 as a graduate student. Since then, we have studied several aspects of the ecology of this island population comparing this with the ecology of anoles on the mainland.

The existence of such island populations enables scientists to carry out natural experiments that provide invaluable information helping us to understand ecological and evolutionary processes.

This Clouded Anole (Anolis nebulosus) species that is on San Agustin Island is endemic to Mexico, and is of particular interest as this population has evolved in the absence of similar species of the same genus, or congeners. The species on the island also occupies a broad niche of perch height and a low number of lamellae, and is one of the most sedentary anoles known. Our work demonstrated that San Agustin population of the Clouded Anole has distinct morphological and genetic traits compared to conspecifics on the mainland.

Recently, we found that the insular population also presents distinct ecologic traits compared to those of the mainland population. In our manuscript “Assessing the relative importance of intra- and interspecific interactions on the ecology of Anolis nebulosus lizards from an island vs. a mainland population”, we suggest that the processes that drives the ecology and evolution of this insular population (intraspecific competition) differs from those that are important in the mainland (interspecific competition).

We believe that the results of our research on the insular population of anoles on San Agustin Island complement the scenario of Caribbean anoles, where congeneric competition is the key evolutionary driver. Furthermore, in our study, we used video cameras to provide direct evidence of predation, interspecific and intraspecific encounters and aggression, which was possible because the Clouded Anole is a sedentary lizard.

It has been a pleasant and rewarding experience for me to study the Clouded Anole. Although spending hours in the field observing a largely sedentary lizard may seem a little boring and tedious, the data from our studies have revealed a fascinating adaptation to the natural and social environment with unique physical, genetic, and ecological characteristics.

Currently, the population of Clouded Anoles on San Agustin has been dramatically reduced, almost to the point of extirpation. We think that two natural events, the hurricanes Jova in 2011 and Patricia in 2015, as well as invasive studies such as Hernández-Salinas et al. (2016) where they extracted 77 anoles from this small island, are the cause of the dramatic reduction in the Clouded Anole of San Agustin Island. As ecologists, we believe that research should not be done at the expense of the species or population under study, but should ensure that the population remains intact to continue along its evolutionary path, and further elucidate our understanding of the natural world around us.

We are currently monitoring both insular and mainland populations in order to understand and evidence the ecological implications of such natural and anthropogenic reduction on anole populations.

SICB 2018: Heat Stress and Deformed Faces

EmbryosIncubation temperature is an important factor in development for anoles (and other ectotherms). Thom Sanger, a professor at Loyola University in Chicago, IL, presented his research on how high temperatures affect brain formation in developing anole embyros. With the help of undergraduates and a high school summer intern, Dr. Sanger found that when developing eggs were heat-shocked, many embryos were lost (75%), but for those that survived, forebrains became smaller (In the figure, A is normal and B is deformed). Interestingly, malformation of the forebrain affects the size and shape of the face, and so surviving heat-shocked embryos exhibit cranial malformations. As Sanger continues his research, he will follow a neural degeneration hypothesis, which boils down to (no pun intended) the idea that thermal stress increases the rate of cell death, and the amount of cell death affects facial shape. While the effects of high temperature may seem alarming, Sanger notes that this does not happen very often in nature; females are generally pretty good at selecting suitable nest sites. But, because development is similar across reptile taxa, anoles can be an excellent model system to inform predictions about what may happen to species that are in danger.

Origins and Biogeography of the Anolis crassulus Subgroup

Anolis morazani. Photo by Josiah Townsend from iNaturalist.

The Anolis crassulus subgroup contains ten morphologically-conserved highland anole species found throughout Nuclear Central America. Its members have long been a source of headache for region’s systematists. To quote Meyer & Wilson (1971): “…specimens of the crassulus group from Guatemala and Mexico have a bewildering array of admixtures of the distinctive characters observed in Honduras… The inter-relationships of the populations… [of the crassulus group] are exceedingly complex, and… we are unable to suggest a satisfactory arrangement.” This was followed up 21 years later by McCranie, Wilson, & Williams (1992): “Clearly, a thorough analysis of crassulus-like specimens from throughout their range… is sorely needed”, and repeated by McCranie & Köhler (2015) 13 years after that.

Despite the need for a thorough investigation into this group, our understanding of the relationships and validity of these taxa has not improved much. This is partly because this subgroup has been poorly represented without broad sampling in larger-scale molecular phylogenies. Two samples in particular, an A. crassulus (from Chiapas, Mexico) and an A. sminthus (from Olancho, Honduras), have been continuously utilized, without additional samples from these species. Most recently, Nicholson et al. (2017; six species) and Poe et al. (2017; three) expanded the molecular sampling for this group, using single exemplars as part of broader analyses.

In a study published last month in BMC Evolutionary Biology, Josiah Townsend and I examined the evolutionary relationships of the majority of this subgroup, in order to provide a starting point for resolving some of the confusion surrounding these taxa.

Figure 4 from Hofmann & Townsend, 2017. Species tree of the Anolis crassulus subgroup. Inset photo: Anolis heteropholidotus (2) by JHT.

Fig. 4 from Hofmann & Townsend, 2017: Species tree of the Anolis crassulus subgroup. Black nodes indicate PP > 0.95; PP < 50 not shown. Inset photo: Anolis heteropholidotus (2) by JHT.

The results of our multilocus phylogenetic investigation gave us some interesting new insights into the subgroup. We found support for the monophyly of the A. crassulus subgroup relative to other Anolis (as opposed to its paraphyly, as recovered in Poe et al. 2017), and the validity of all of its species (excepting the two we could not sample). Additionally, we recovered considerable overlooked diversity within this subgroup. Anolis crassulus itself represents at least four lineages corresponding to distribution: the Chortis Highlands of Honduras, the Salvadoran Cordillera, Guatemala, and Chiapas, Mexico. Surprisingly, the sample from Chiapas previously used in many phylogenies was recovered as an undescribed lineage sister to A. anisolepis, not conspecific with any of the four A. crassulus lineages, including another Chiapan lineage. We also recovered the widely-used “A. sminthus” sample (which was previously hypothesized by McCranie and Kohler (2015) as representing an undescribed lineage more closely related to A. crassulus) as an undescribed lineage sister to A. morazani, and found additional mitochondrial lineages within A. heteropholidotus and A. rubribarbaris. Diversification within the group was estimated to have started in the early Miocene in the Chortis Highlands (supporting the results of Nicholson et al. 2017), with the Honduran population of A. crassulus diverging from the other three lineages approximately 13 MYA.

Figure 5 from Hofmann & Townsend, 2017. Chronogram showing results from divergence dating and ancestral area reconstruction analyses. PP shown when < 1.

Fig. 5 from Hofmann & Townsend, 2017: Chronogram showing results from divergence dating and ancestral area reconstruction analyses. PP shown when < 1.

Given the relatively deep divergence times within this group when compared with the apparent lack ecological and morphological diversification, we hypothesized that this subgroup represents a non-adaptive radiation, though extensive study is necessary to determine if these traits are as conserved as they appear. A taxonomic revision of the Chortis Highland population of Anolis crassulus is being finalized, but a great deal of work remains in order to improve our understanding of these highland anoles.

SICB 2018: Evo-Devo of Anole Digits

Griffin

One more update from the SICB conference in San Francisco last week!

Across vertebrates, the ratio of lengths of the second and fourth digits of the hand are influenced by testosterone and estrogen. This could be of particular importance in species such as anoles, in which the fourth digits of the hindlimbs are extremely long and critically important in locomotion, but previous studies of the 2D:4D ratio in anoles have produced varying results. In the final poster session at SICB, undergraduate Griffin McNamara, working with Bonnie Kircher in Marty Cohn’s lab at the University of Florida, presented preliminary results from a study of cleared and stained brown anole (Anolis sagrei) hind feet. Griffin has big plans for continuing this work, so watch for future publications with these findings!

SICB2018: Density and Timing of Hatching Impact Survival and Growth in Anolis sagrei

Dan Warner (left) and Tim Mitchell (right) beside their poster on impacts of population density and time of hatching on survival and early life phenotypes of Anolis sagrei

Dan Warner (left) and Tim Mitchell (right) beside their poster on impacts of population density and time of hatching on survival and early life phenotypes of Anolis sagrei

Tim Mitchell a post-doctoral researcher at University of Minnesota with Emilie Snell-Rood presented his work from his prerious post doc in Dan Warner’s lab where he investigated the impacts of density and timing of hatching on the survival and growth of Anolis sagrei hatchings. Seeking to specifically address these questions:

How does investment in offspring size and number shift seasonally?

Does the timing of hatching influence survival or growth in the field?

And does adult density influence survival or growth of hatchlings in the field?

Adult anoles were brought into the lab on three different dates and breeding was split into three corresponding windows of time: Cohort 1 (February 23rd – April 27th), Cohort 2 (June 18th – July 30th), and Cohort 3 (September 5th – October 15th).  On experimental islands, adult densities were manipulated to create high and low lizard densities. Hatchlings from cohorts 1, 2, and 3 were released onto high and low adult density islands in June, August, and October, respectively, and researchers returned the following spring to recapture the marked lizards.

Breeding in the lab revealed a seasonal shift from producing more smaller offspring early to producing fewer larger offspring later in the season. Adult densities on the islands did not affect hatchling survival, but there was a substantial survival advantage to being an early-hatched lizard. Size and growth of hatchlings were influenced both by timing of hatching and the adult densities. So happy to catch up with my academic family and see the cool research they are doing!

SICB 2018: Bigger Testes Don’t Produce Bigger Sperm

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In the face of mate competition, sperm morphology can vary in a way that can enhance an individual’s chances of siring offspring of females. Studies in the past have attributed increased relative testis size as an approximate measure of an individual’s response to sperm competition. However, this does not take into account the internal architecture of the male testes that may contribute to changes in sperm morphology.

This was the focus of a poster presented by Hanna Hall titled “The evolution of sperm and testis morphology in Anolis lizards” in collaboration with Ariel Kahrl and Michelle Johnson. The authors sampled 2-20 individuals of different species of anoles in Puerto Rico and the Dominican Republic. They compared body size, sperm length ( 15 cells per individual), and the composition and size of various layers of the testis, by conducting a phylogenetic least squares regression on the average values obtained for each species.

The authors found that larger body size was associated with a larger testis size, which was in turn correlated with presence of large seminiferous tubules and a larger luminal area, where mature sperm are stored. Contrary to their expectation though, none of these aspects were associated with producing longer sperm. Further the Gonado-Somatic index (GSI), a common metric that serves as an indicator of relative testis size, was not correlated with any aspects of the internal testis architecture.

An interesting finding in this study was that species with a higher proportion of epithelial cells in the testis produced longer sperm. This result was surprising because larger number of epidermal cells may be associated with smaller spermatogonal cells, which would be predicted to form shorter sperm. The authors suggest that the correlation between lumen area and testis size may result because investment in sperm storage is more important, and that species may be producing large number of sperm which may be longer in length. Nevertheless, more data is needed to understand how changes in sperm morphology affect fertilization success and, further, under what circumstances does size and count of epithelial cells vary. The lack of correspondence of these results with that  shown in birds by Lupold et al. 2008 suggests that the mechanisms underlying sperm competition may be taxa or species-specific. We will be eyeing the Johnson Lab for more details on the same in the coming years.

SICB 2018: Role of Testosterone in Mediating Female Aggression in Anolis Lizards

An example of an aggressive display by a lizard. Photo Credits: Neil Losin Photography

An example of an aggressive display by a lizard. Photo Credits: Neil Losin Photography

Testosterone has long been though to influence male aggression behaviors. But can this same hormone influence aggressive behaviors in females too? Ellee Cook addressed this question in her talk titled “Investigating the potential for testosterone to mediate territorial aggression in female Anolis lizards.”

Ellee focused on studying a population of Anolis gundlachi in the forests of Puerto Rico. Ellee studied the response of focal females to a staged territorial intrusion by another female who was placed on a cage lid, and compared it to a scenario where she directly approached the lizard. She captured the focal females after twenty minutes of the trial and measured their size and took a blood sample to estimate the circulating levels of testosterone. Her prediction was that higher levels of aggression would be correlated with higher levels of testosterone.

Her data showed that females were indeed aggressive towards intruding females and had much higher displays of aggression in comparison to when they were presented only a lid or were directly approached. Surprisingly (or not so surprisingly), testosterone was not a significant predictor of female aggression. In fact, none of the hormonal measures corresponded to female aggression. This finding could have resulted for several reasons: A) the amount of testosterone detected in females was much lower than that found in males, making variation in testosterone  almost impossible to detect; B) High aggression may be caused by spontaneous spikes in testosterone that may be hard to detect; C) Female aggression may be governed by a completely different mechanism.

This study raises an important question about the relevance and drawbacks of existing paradigms which are male-centric and thus cloud our understanding when it comes to female behaviors. Cheers to more feminist paradigms in biology!

SICB 2018: Local density of conspecifics affects sperm phenotypes in wild Anolis sagrei lizards

Theory predicts that males should invest more in ejaculate production when the likelihood of sperm competition is high, thereby increasing the chance of fertilization. However, ejaculates can be energetically costly, and increased investment into sperm production should only occur if there are fitness benefits associated with that increased investment. Growing experimental evidence suggests that sperm traits respond plastically to social environment. However, it is not known whether fine-scale spatial variation in the local density of male competitors or potential female mates corresponds to individual variation in ejaculate production.

Island population with capture records of males (blue) and female (red) anoles.

Island population with capture records of males (blue) and female (red) anoles.

Matt Kustra of the Cox lab examined a wild population to test the prediction that, as the risk of sperm competition increases (i.e., higher local density of male competitors), males will increase their total investment in their ejaculates (sperm count). He also tested for correlations between sperm morphology, specifically midpiece size and local density.

To do this, he and the Cox lab collected wild adults from an island population in Florida. They generated a map of each tree on the island using ArcGIS, then marked the location of males and females on this map. Using the kernel density function, they estimated the local density of individual males by taking into account all conspecific adults that were captured within a 5.8 m radius of an individual’s own capture location.

Matt found that length of the sperm midpiece increased with local density, whereas length of the sperm head and sperm count decreased with local density. Contrary to his predictions, he found that total investment in sperm count decreased with local density. This could be because males in high density environments have depleted their sperm stores because they have more opportunities to mate, or it could be because males are investing less per ejaculate if mating frequency is higher.

These findings indicate that fine-scale differences in local density within a wild population can affect sperm count and various sperm phenotypes. In the future, the Cox lab hopes to measure fitness in this populations to understand how sperm phenotypes shape individual reproductive success.

SICB 2018: Variation in metabolic rate among Anolis oculatus ecotypes on Dominica

Whereas in the Greater Antilles islands anoles evolved ecomorphs and live in communities with up to 11 species in sympatry, islands in the Lesser Antilles support only one or two species each. However, islands such as Dominica have populations of anoles that experience selective pressures resulting in different ecotypes.

Dominican Ecotypes

Figure from Thorpe et al. 2004

While Dominica is relatively small, the mountainous topology results in highly variable environmental conditions across the island with cool mountainous regions and warm coastal regions and thermal vents. The single endemic anole species present on the island, Anolis oculatus, exhibits four morphologically distinct ecotypes (Montane, Atlantic, North Caribbean and South Caribbean) and despite levels of gene flow between these ecotypes are high, adaptive differentiation in this system is maintained.

Photo by Aurélien Miralles

Photo by Aurélien Miralles

Tricia Neptune, a graduate student in the Watson lab, at Midwestern State University, explored whether these ecotypes also show any differences in metabolic rate (by measuring oxygen consumption) and its sensitivity to temperature (Q10) at ecologically-relevant temperatures.

Results show that size differences between ecotypes are reflected in their physiology with the south Caribbean ecotype exhibiting higher oxygen consumption and Q10 compared to the other three ecotypes. Tricia hypothesize that these differences in metabolism and temperature sensitivity are in part responsible for maintaining relaxed geographic segregation among ecotypes.

Tricia plans to incorporate data on sprint speed, bite force as well as investigate thermoregulation strategies in this species. It will also be interesting to see a comparative study between the A. oculatus ecotypes and the introduced Puerto Rican crested anole, A. cristatellus.

Figure from Thorpe et al. 2004

SICB 2018: Ecomorph Claws in Greater Antillean Anoles

The cover slide of Michael Yuan's talk at SICB 2018.

The cover slide of Michael Yuan’s talk at SICB 2018.

Convergent forms of anoles can be found across the Greater Antilles, with similar phenotypic and ecological morphs filling similar microhabitats from island to island.  Anole ecomorphs are in part defined by the extent of arboreality, as most species in the Greater Antilles spend a lot of time in trees.  Crandell et al. 2014 found arboreality to be associated with significant differences in claw characteristics in Costa Rica and Panama.  In Greater Antillean anoles, similar research into claw morphology has yet to investigate if this relationship holds across ecomorphs. Michael Yaun, a PhD student in the Wang lab at UC Berkeley, set out to investigate the patterns of variation of claw morphology in the Greater Antillean anoles.

Anolis barbouri is shown as an outlier in a PCA. The flattened claws of this ground-dwelling anole are illustrated in black to the right.

Anolis barbouri is shown as an outlier in a PCA. The flattened claws of this ground-dwelling anole are illustrated in black to the right.

Michael sampled 566 individuals, which included 55 species of anoles, all 6 ecomorphs, and another 8 species without any ecomorph designations.  His results suggest that perch height and diameter produced differential effects on claw characteristics.  Performance traits like toepad lamellae number and area were not correlated with claw height and length.  Michael’s study uncovered only one anole that conformed to previous research: Anolis barbouri, the only truly terrestrial species in the data set, possessing flattened claws.  Intriguingly, twig anoles have the most divergent claws, an inspiring result for future directions!

SICB 2018: Unraveling Natural and Human-Mediated Founder Events in Anolis carolinensis

Photo by Andrea Westmoreland

Photo by Andrea Westmoreland

Human-mediated range expansion is rapidly forming novel populations of anoles. The ancestry of these new populations typically traces back to a handful of individuals, and with repeated invasions the genetic history can be complex. These scenarios may be common in non-native populations of Anolis carolinensis, but what does the genetic history look like in such a system? In Sozos Michaelides’ talk at SICB 2018, he discussed his recently published findings.

Michaelides et al., 2017 tackled the question by inferring colonization history using mitochondrial haplotypes from Hawaiian Islands (Oahu, Hawaii, Maui, and Lanai) and some western Pacific islands (Guam, Palau, Saipan, Yap, and Rota). After genotyping 576 anoles, population genetic diversity and differentiation was assessed between native and non-native ranges. Results indicated geographically disparate haplotypes were identical (Hawaii to Brownsville, Texas), demonstrating that source populations may be from Texas or Louisiana. And a minimum of two introductions to Hawaii and Guam were uncovered, with subsequent within-population stepping-stone model colonization.

Overall, lower genetic diversity was found in non-native island populations as distance increased from the southeastern United States source population, and between the two archipelagos, genetic differentiation was high. Persistence of these non-native populations is not guaranteed because they are isolated, small in population size, and low in genetic diversity. It will be interesting to study the adaptive response of these introduced populations to stochastic climatic events!

SICB 2018: Insulin-Like Growth Factors and Anole Cells

IMG_0677

The insulin signaling network has an essential role in growth, reproduction, and aging. Insulin-like growth factors, or IGFs, are important protein hormones within this network and are typically conserved across vertebrates. However, some proteins in the insulin signaling network have experienced selection in reptiles. Also, not a whole lot is known about the specific functions of components of this network within reptiles.

Amanda Clark, a PhD student in Dr. Tonia Schwartz‘s lab at Auburn University,  investigated the the function of purified IGFs on cell function for brown anoles (Anolis sagrei) and crested anoles (Anolis cristatellus). She had five different treatments for cell plates from both species: brown anole (BA) IGF-1, BA IGF-2, green anole IGF-1, a positive control, and a negative control. Cell proliferation was not different among all of the treatments, possibly due to incorrect protein folding or low concentrations of IGF. As expected, cell viability was also not affect by the IGFs. In the future, this experiment will be conducted again with increased sample size and an improved positive control.

SICB 2018: How Many Neurons Are in An Anole Brain?

Across species, bigger brains usually mean better cognition. But, this relationship rarely holds when considering individual differences within a species. Within species, the number of neurons in the brain may be a better proxy for cognitive ability than brain size. Further, the number of neurons may be independent of brain size.  But how to measure neuron number?

levi

Levi Storks, a graduate student in Manuel Leal’s lab at the University of Missouri, set out to do just that. He adapted a protocol that has previously been used in mammals, birds, and crocodiles, but never before in lizards. In brief, he dissected the telencephalon, cerebellum, and other regions of the brain of an Anolis cristatellus and used the isotropic fractionator method to determine neuron number in each of the three. After homogenizing each tissue, he used a double-labeling technique with DAPI to stain each nucleus and neuronal nuclei antibody to stain each neuron, and used a hemocytometer to count the cells under magnification. Now that this protocol is working, look out for Levi’s future results on anole brain structure and cognition!

SICB 2018: How does muscle fiber number, size, and behavioral use vary across anole lizards?

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Muscle growth and development occur via different physiological mechanisms across the animal kingdom. Variation in behavioral uses of muscle may lead to the evolution of different muscle sizes across animal species. Different-sized muscles may vary in their capacity for strength or frequency of use and larger muscles may develop as the result of possessing higher numbers of muscle fibers, larger muscle fibers, or a combination of the two. Jesus Vega, an undergraduate student with Michele Johnson at Trinity University, was interested in learning how muscle size evolves across anole species by studying the retractor penis magnus (RPM), used to retract the hemipenes back into the tail.

Testing a hypothesis that larger RPM muscles will have more or larger muscle fibers, due to an expected evolutionary trade-off between fiber number and size, Jesus examined copulation behavior data and RPM muscle traits of 24 species of anoles. Behaviorally, there was no correlation found between copulation rate and RPM muscle fiber size or number. Physically however, species that have larger RPM muscles have more RPM fibers, species with larger muscle fibers have RPMs with more fibers, and species with larger bodies have more RPM muscle fibers and larger RPM muscles. These results show that larger muscles evolve due to increased muscle fiber size and number and also suggest that copulation behavior is not associated with muscle size evolution in anoles.

SICB 2018: What is the Relationship between Neuropeptide Y, Corticosterone, and Hunger in the Brown Anole?

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Neuropeptide Y (NPY) is a hypothalamic appetite-stimulating regulator of food intake that has been suggested to interact with components of stress response, including the release of the stress hormone corticosterone (CORT). Recent work suggests that NPY can interact directly with the adrenal gland to promote CORT secretion, raising the question of whether NPY can stimulate a stress response and whether NPY requires an active stress response to regulate food intake. This interaction has been examined in mammals but the role of NPY has not been explored in reptiles. To answer questions about the relationship between NPY, stress, and food intake in reptiles, Micaela Castro, a student with H. Bobby Fokidis at Rollins College, performed two manipulative experiments, one in the field, and one in the laboratory, on the brown anole (Anolis sagrei). These experiments utilized injections of NPY and dexamethasone (DEX), an agonist that inhibits CORT secretion, to test the hypotheses that NPY promotes CORT secretion and food intake and that CORT secretion is required for NPY to exert its appetite-stimulating effect.

In the field, adult male brown anoles were captured and injected with varying levels of either NPY, DEX, or saline as a control. An hour after injection, blood was collected and CORT levels were measured. From this study, it was found that NPY injections promoted CORT secretion while DEX injections decreased CORT secretion relative to the saline control. In the laboratory, adult male brown anoles were fasted for either 24 hours or 48 hours, injected with either NPY, DEX, DEX followed by NPY after an hour, or saline as a control, and were observed for differences in food intake. From this study, it was found that DEX injections decreased food intake relative to controls while NPY injections increased food intake relative to controls, but only when anoles were fasted for 48 hours. DEX injections followed by NPY injections resulted in similar food intake to control animals. All together, these results suggest that NPY and CORT are codependent, with NPY capable of stimulating CORT secretion and CORT being required by NPY for it to exert its appetite-stimulating effects.

SICB 2018: Sperm storage and multiple paternity in brown anoles

Sperm storage is widespread in all major reptilian taxa and in combination with multiple mating it could have indirect benefits in polyandrous systems for example by increasing genetic diversity among offspring. Hannah Marshall, a junior majoring in Biomedical Sciences at Auburn University in Tonia Schwartz’s lab, set out to test the utility of microsatellite markers in paternity analysis in a population of brown anoles, Anolis sagrei, in Florida and to assess the extent and pattern of sperm storage from field matings.IMG_20180106_155824

Brown anoles from the field were housed in pairs (control) and in groups of four (2M:2F) and six (3M:3F) in 23 experimental laboratory enclosures. Eggs were collected over one breading season and hatchlings and their candidate parents were genotyped at seven microsatellite loci. The software CERVUS was used to determine the most probable parental pair for each hatchling and to disentangle paternity from experimental males to sperm storage.

Results show that these markers are sufficiently polymorphic to allow paternity assignments with high confidence. With regards to the use of stored sperm, 58% of the eggs produced in the lab were from field matings, which is consistent with previous findings in Anolis sagrei. However, Hannah’s data suggest that these lizards continue to use their stored sperm up to 4 months, longer than previously documented.

These findings are preliminary and Hannah is currently collecting and analyzing more data from these experimental enclosures. Understanding the dynamics of reproductive output in this focal population is valuable for planning further experiments to measure fitness.

SICB 2018: Anole Size Matters to Urban Predators

Urbanization changes many factors, such as temperature and food availability, that influence body size in animals. Last year at SICB, Zach Chejanovski presented on this topic in brown anoles from Miami (Anolis sagrei). He found that predator (curly-tailed lizards) abundance was highly associated with body size in anoles. As predator abundance increases, anole body size increases. Chejanovski, a PhD student at the University of Rhode Island, then formed a new question based on his previous findings: Are larger anoles actually predated on less often than smaller anoles?

Male brown anole showing his dewlap

Male brown anole showing his dewlap. Photo by Renata Brandt

To answer this question, Chejanovski performed a tethered intruder experiment with male brown anoles of variable sizes. For each trial, he tied an anole at the end of a pole and presented the anole to a curly-tailed lizard. He then recorded the amount of time for the predator to get within 20 cm of the anole. Results from a survival analysis show that smaller lizards were attacked more often and more quickly than larger anoles. According to this experiment, larger body size in brown anoles results in less predation from curly-tailed lizards. However, is body size genetically determined?

Curly-tailed lizard

Curly-tailed lizard

Chejanovski then set up  a common garden experiment with female anoles from urban sites with and without curly-tailed lizards. Eggs were collected from these anoles, incubated, and allowed to hatch. Hatchlings were raised in identical lab conditions and measured for body size to calculate growth rate. Male anoles from predator sites grew faster than males from non-predator sites. These results suggest that body size has some genetic control in males. However, female growth rates did not differ between sites. The discrepancy between sexes may be due to different selective pressures, such as sexual selection. This work highlights the importance of body size  in urban environments with predators.

 

SICB 2018: Does urbanization alter the way anoles move?

Urbanization is a global issue that alters the way many natural populations survive and reproduce. The construction of new developments, housing, and other man-made structures alters the environment available to many species of lizard, and anoles perhaps most famously. Urban anoles in Florida and other parts of the southern United States are a common feature in many cities, why, everybody that attended SICB 2015 in West Palm Beach, Florida remarked that there were anoles on almost every tree! Particularly, the addition of artificial and smooth substrates poses a concern to many species of arboreal lizard that need rough and heterogeneous surfaces in order to climb and run effectively. The differences in structural habitat available to these anoles can in turn affect their morphology, leading to evolutionary changes in body shape and form over time to better adapt to urban lifestyles. Andrew Battles, a PhD student with Jason Kolbe at the University of Rhode Island, recognized this problem and designed a clever experiment to understand just how smoother surfaces impact the running ability of anoles.

Andrew sampled crested anoles from two sites: an urban and a natural site, and used a series of running experiments to understand how the addition of smooth, urban substrates affects the ability of anoles to move. Using two different inclinations (37 and 90 degrees), 2 substrates (smooth and rough), and the running power of 13 crested anoles, they found that anoles exhibit a decrease in speed due to increasing incline, and exhibited slower speeds on a smoother track relative to a rougher one. They also found that stride length decreased on smooth and vertical tracks, and that urban and natural anoles responded similarly to these changes in substrate and incline. They also found that anoles will try to change their gait and increase their stride width due to incline, but not so much on different substrates. Their major take-away was that smoother substrates do decrease lizard sprint performance, which is a fundamental trait for a lizard to survive and reproduce. And while there are no differences between habitat types, the build-up of urbanization over time might lead to evolutionary shifts for crested anoles in urban environments so that they might better adapt and live in cities. Keep up the stellar experiments, Andrew!