Two recent talks at JMIH 2017 shed light on key morphological characters in anoles: toe pad shape and limb length. Travis Hagey presented his work which looks to shed light on why lizard toe pads are shaped the way that they are and addresses whether gecko and anole toe pads are convergent structures. Working with a team of undergraduates, Travis used geometric morphometrics to analyze the structure of toepads in a diverse group of geckos and anoles. Travis found that anole and gecko toe pads have a similar range of values for traits such as the placement of pads on the toes and the shape of the toes (skinny or fat) in relation to claws. However, anole toe pads formed a distinct cluster indicating that they occupy a unique area of trait space not used by geckos. This finding suggests that the divergent evolutionary history of anoles and geckos has resulted in independent evolutionary explorations of toe pad shape.
Immediately following Travis’ talk, Robin Andrews presented work investigating the embryological development of morphological characters in diverse lizard species. In anoles, consistent differences in the morphology of divergent species support the existence of different anole ecomorphs. Previous research by Sanger and colleagues has shown that the differences in limb-length between anoles of different ecomorphs have their origins early in embryonic development. These early differences in limb length continue throughout the development of anoles into hatchlings and adult forms, a pattern known as transpositional allometry.
Robin compared patterns of limb, tail, and head growth in early stage embryos of four different lizard species, including a chameleon, two geckos, and the brown anole (Anolis sagrei). She found that species-specific differences in limb and tail lengths were exhibited as soon as limb and tail buds emerged from the body and were both best characterized by the same pattern, transpositional allometry. Embryonic head growth, however, showed no specific pattern. Robin’s findings suggest that the adaptive evolution of adult morphology in anole ecomorphs as well as other diverse lizard species is underpinned by developmental reprogramming.
Travis Hagey, Jordan Garcia, Oacia Fair, Nikki Cavalieri, and Barb Lundrigan: Variation in Lizard Adhesive Toe Pad Shape
Robin Andrews: Developmental Origin of Limb Size Variation in Lizards
All anole field biologists have been there, right? It’s the middle of the night, and you’re walking around the forest searching for sleeping lizards in the trees. You’re probably wearing a headlamp, so the bugs are flying around your face, and your eyes start to strain as you get sleepy and you’re entering hour three or four of the search. This searcher fatigue could lead to the kinds of unintentional bias that can interfere with our research. But there’s good news when it comes to anoles, as Amy Yackel Adams, a statistician with the USGS in Fort Collins, Colorado, reported on the last day of JMIH.
Dr. Yackel Adams works with a Rapid Response Team whose goal is to prevent the spread of the worst invasive species. When a report came in of a sighting of a brown tree snake on the island of Saipan (in the Northern Mariana Islands, western Pacific Ocean), the team of experienced herpers deployed to Saipan and began intensive nightly surveys to assess the possibility of a brown tree snake population there. Luckily, they didn’t find any of these snakes in the surveys, but they did log 20,000+ sightings of other vertebrates! These included emerald tree skinks, several species of geckos, a variety of small mammals, and the green anole (Anolis carolinensis). Dr. Yackel Adams saw an opportunity to use this rich dataset to statistically test for two types of bias that could occur in such surveys – searcher fatigue (both across the 4-hour nightly searches, and across the up-to-31 day deployment), and searcher bias in taxon detection.
The team of 29 searchers covered a total of 387 km of transects during the 31 days, and found a total of 5,800 sleeping green anoles during this time. (Wow!!) In terms of short-term searcher fatigue, there was a slight decrease in tree skink and mammal sightings as the night progresses, and gecko sightings were generally stable over the night, but far MORE green anoles were sighted in the later hours of the night. And over the long term, skinks and anoles were MORE likely to be detected the more nights a searcher worked, and there was no evidence of long-term searcher fatigue. So, that’s why my take-home message was “nobody gets tired of looking for anoles!”
There was, however, significant taxonomic bias among the searchers – for example, the skink-to-anole sighting ratios ranged from 0.86 to 9.5. Dr. Yackel Adams concluded that this type of bias could be a real problem for certain kinds of studies, and we should be aware that differences among sightings by our survey team members could be potentially problematic in statistical analyses.
In their 2008 review “Are islands the end of the colonisation road?” Bellemain and Ricklefs (2008) concluded that oceanic islands could be important sources of colonisation of mainland continental areas and cited anoles of the Norops clade as a notable success. There are more than 5 times as many Norops clade species in Central and northern South America as in the West Indies; the 23 extant Caribbean species in the clade are distributed in Cuba and Jamaica with one species in Grand Cayman (Nicholson et al, 2005). Data in Nicholson et al (2005) gave support to the reverse colonisation hypothesis, but did not offer specific dating for the colonisation.
New analyses of 65 species in the Exophthalmus weevil genus complex (Zhang et al 2017) have turned up results that are of significance in understanding the biogeographic history of Caribbean anole dispersal and diversification. Like anoles of the Norops clade, the weevils show reverse colonization (island-to-continent), with diversification on the mainland and diversification within the islands. The data also give some support for overwater dispersal as the factor best explaining ancient between-island distribution.
Zhang et al’s best fit biogeographic model gives an estimate of 19Ma for a jump dispersal of Exophthalmus, most likely from Hispaniola, which went on to diversify into more than 40 species in Central America. So – did the anoles and the weevils make their journeys to the mainland around the same time and under similar conditions? Can this weevil study and the techniques it uses to arrive at its conclusions inform anole evolution and dispersal?
Bellemain, E and RE Ricklefs (2008) Are islands the end of the colonisation road? Trends Ecol Evol. 2008 Aug; 23(8):461-8. doi: 0.1016/j.tree.2008.05.001. Epub 2008 Jun 26. (Correction to citation numbering: Trends Ecol Evol. 2008 Oct; 23(10):536-7).
Nicholson, KE, RE Glor, JJ Kolbe, A Larson, S Blair Hedges, JB Losos (2005) Mainland colonization by island lizards. Journal of Biogeography 32 (6), 929-938.
Zhang, G, U Basharat, N Matzke, NM Franz (2017) Model selection in statistical historical biogeography of Neotropical insects—The Exophthalmus genus complex (Curculionidae: Entiminae). Molecular Phylogenetics and Evolution, 109, 226-239. DOI: 10.1016/j.ympev.2016.12.039.
For most of the history of life on earth, the only sources of light at night were the moon and stars. Yet with the invention and rapid spread of electric light, species around the world now face a novel evolutionary pressure: artificial light at night, or ALAN. Artificial light likely has an especially strong effect on animals in city habitats, such as the urban-adapted brown anole lizard, Anolis sagrei. Chris Thawley and Jason Kolbe at the University of Rhode Island set out to determine whether brown anoles were negatively impacted by ALAN.
In addition to their abundance in urban environments, brown anoles are a particularly good species for this study. Previous studies of brown anoles have shown that photoperiod influences the onset of reproduction at the beginning of the breeding season, and that several behavioral traits change under artificial light. In addition, work by Moore and Menaker has shown that pineal production of melatonin in this species is significantly altered by photoperiod. So, would ALAN influence brown anole growth and reproduction?
Chris and Jason collected lizards from south Florida and set up a lab experiment where some lizards experienced a normal photoperiod, and others were exposed to ALAN that mimicked landscape lighting. Their results were quite unexpected! ALAN actually increased female growth, resulted in eggs laid earlier in the season, and increased the reproductive output of small females – but did not affect the number or mass of eggs or hatchlings. And, ALAN females did not exhibit more stress (measured via circulating corticosterone) than control females.
So are brown anoles just superlizards? Do they have no trade-offs that result from ALAN? Chris suggested that it’s possible that such trade-offs may appear in studies over a longer time period, or in traits not measured here. Or, perhaps ad libitum food and the absence of predators in the lab remove the costs of ALAN. Or, maybe these really are indefatigable lizards!
An extensive body of work has addressed the eco-evolutionary impacts of the Northern Curly-tailed Lizard (Leiocephalus carinatus) on Brown Anoles (Anolis sagrei) (much of it receiving coverage right here, here, and here on Anole Annals!). These species co-occur not only on many Caribbean islands where much of this research has taken place, but also within the urban matrix of southern Florida, where both species are introduced.
Camila Rodriguez-Barbosa and Steve Johnson investigated the impacts of curlies on brown anoles in shopping centers in southern Florida where both species were plentiful. Camila first collected baseline data on anole and curly populations at eight sites before embarking on a quest to eliminate curlies from four of her sites. Over the next four months, she removed over 300 (!) curlies from these sites, many of which had brown anole remains in their stomachs.
She found that this removal had serious consequences for brown anoles. Compared to anoles from shopping centers where curlies were unchanged, A. sagrei at removal sites experienced higher survival and consequently greater abundances. These anoles also shifted to lower perches once curlies were removed, mirroring results from previous work which show that the introduction of curlies leads to brown anoles occupying higher perches to escape this dangerous predator. Camila’s work suggests that brown anole/curly-tailed lizard interactions may be similar even in very different habitats and provides a fascinating look at lizard life (and death) in the urban sprawl of southern Florida.
Sometimes a scientist just needs hundreds of hatchling anoles for an experiment. Tim Mitchell found himself in this position recently, and, like a good lizard ecologist, he started breeding colonies of anoles in the lab to produce eggs to incubate until hatching. As he created three different breeding colonies from brown anoles (Anolis sagrei) in central Florida, one each in February, June, and September, Tim found that he had also created an ideal situation in which to examine how the reproductive condition and output of brown anoles varies across the breeding season.
Tim, along with his coauthors Josh Hall and Dan Warner, found that females produced eggs with significantly greater mass later in the breeding season. These eggs took longer to produce than those earlier in the year (a greater interclutch interval), and the eggs resulted in hatchlings that had higher mass in relation to the weight of their eggs. These reproductive differences remained even after accounting for the fact that female anoles were also larger and heavier later in the year.
These findings suggest that female A. sagrei may shift their reproductive effort from producing a higher quantity of eggs (i.e., more, smaller eggs resulting in smaller hatchlings) in the beginning of the breeding season, to producing higher quality eggs (i.e., fewer, larger eggs resulting in larger offspring) later in the breeding season. Tim’s findings also stress the importance of investigating and accounting for seasonal differences when examining reproductive output in lizards.
Greetings from Austin, Texas, and the Joint Meeting of Ichthylogists and Herpetologists! Chris Thawley and I have appointed ourselves to be your AA reporting team from JMIH, and we’re aiming to post updates from each of the 8 anole talks and posters at this meeting.
On the first day of the conference, there were two exciting talks on the ecology of Costa Rican anoles. The first was by Brian Folt, a graduate student in Craig Guyer’s lab at Auburn, who developed a model of predator-prey co-occurrence where one of the prey were anoles (Anolis (Norops) humilis) and the predators were…spiders?! Yes, wandering spiders, or ctenids, can prey upon the small anoles on the forest floor. (The other putative prey were poison dart frogs, who have a relatively similar life history to anoles.) Brian performed an extensive field study in 14 plots at La Selva Biological Station, conducting visual encounter surveys for anoles, frogs, and spiders, and recording arthropods in leaf litter samples. He used two-species occupancy models to determine how prey were affected by the presence of the predator and by resource abundance in the leaf litter. The result? Anole occupancy was lower where spiders were absent, and the detection probability of anoles was higher when spiders were present and detected. This suggests that anoles are responding behaviorally, such that they may increase their vigilance when predators are around.
I then ran across the conference center to catch the next anole talk – a terrific presentation by Michelle Thompson, a graduate student in Maureen Donnelly’s lab at Florida International University. Michelle studied whether thermal quality differed across the stages of forest succession, and how that affected Anolis (Norops) humilis and A. (N.) limifrons distributions. She worked across transects of pasture, secondary forest, and old growth forest in both upland and riparian sites. Michelle measured the thermal quality of each habitat, the thermal preferences of the lizards, and the location and abundance of the lizards. She found that thermal quality was lowest in the pasture sites, as temperatures were frequently higher than the lizards prefer. Yet, in these pasture sites, riparian habitat with remnant trees provided a thermal refuge for the lizards. This kind of work can help us understand why and how species may respond differently to human-caused alterations in habitat structure and temperature in our changing world.
Stay tuned for updates from JMIH, and follow the #JMIH17 hashtag on twitter for more herp-related news!
Two years ago, McCranie and Kohler published The Anoles of Honduras: Systematics, Distribution, and Conservation(available on Amazon for under twenty bucks and downloadable for free on the Museum of Comparative Zoology website).
In turn, two mostly favorable reviews were published. However, one of the reviews, by Levi Gray, did question whether a number of anole species recognized from small distributions in Honduras should be recognized as valid species, rather than just as populations of species that are widespread throughout Central America.
Writing in Zootaxa, Randy McCranie has now responded to this point, forcefully arguing that the species should be recognized and challenging his critics to present their own data if they feel otherwise. You’ll have to read Gray’s review and McCranie’s rebuttal yourself to decide what you think. Gray made his skepticism clear, he also did clearly call for more research to address the question.
These pages have previously told the tale of Anolis lineatus, the species whose is different on one side compared to the other. Now the work has been published in Breviora. Like all publications of the Museum of Comparative Zoology, the paper can be downloaded from the museum’s publications webpage.
The research project was actually explained in a delightful video put together by the three joint authors, all of whom are headed to college this fall.
Eileen Wickens, who just finished the fourth grade in north central Florida, is a lizard-catching machine and particularly adept at nabbing blue-colored green anoles (Anolis carolinensis). Here’s the story, relayed by her mom, Carissa:
The teal lizards do seem rare as we have only seen a few. We had one at our house last spring and the photo I sent you was taken at our horse teaching unit in Gainesville. We were running an equine behavior trial that day (we’re actually investigating startle phenotypes and genetics in our Quarter Horse herd), and I saw the lizard as we were packing up our gear. My daughter is very good at spotting and catching them, so we will definitely keep our eyes out and would be happy to provide a specimen for your genetic research if we can. I’ve attached the photo of the lizard we had at the house last spring. The green anoles are scare in our neighborhood and on campus compared to the brown anoles (short snouts with distinct, dorsal diamond or striped markings). They seem to far outnumber the greens.
From our brief observations of those two blue lizards this past year it does not appear they turn the bright green you see on the other Carolina Anoles, but it would be good to observe them for a longer period of time to be certain.
In the Greater Antilles, lizard radiations have produced the same suite of ecomorphs on different islands as a consequence of adaptations to similar environments. In the same way, species that use motion-based signals, and occur in sympatry, would be expected to develop similar adaptations to enhance signal efficacy as they are frequently exposed to the same environment (e.g. background noise). Additionally, sympatric species often develop mechanisms to ensure they can distinguish between conspecifics and heterospecifics, particularly if they are closely related. This means that potentially opposing selective pressures might be at work for such systems.
Agamid lizards are widespread across the Australian mainland, and species distributions regularly overlap, especially in arid and rocky habitats. We analysed the motion-based signals of two pairs of sympatric species of Australian agamids to consider how they maintain reliable communication, while at the same time they avoid misidentification during signalling interactions. We calculated the speed distributions of the motion produced by lizard signals, and also by the environment (i.e. background noise). We then compared these two sources of motion to obtain a measure of signal-noise contrast, which indicates how much the signals stand out from the background and is therefore a proxy for signal efficacy (see Ramos & Peters 2017a).
The ring-tailed dragon (Ctenophorus caudicinctus) and the long-nosed dragon (Gowidon longirostris; Figure 1) are often found in sympatry in south Northern Territory and southeast Western Australia, around gorges and rocky outcrops. We recorded territorial displays at West MacDonnell National Park, in Northern Territory. The two species differed in display complexity (example of displays by all four species) and motor pattern use, as well as overall morphology (Figure 2). Interestingly, the speeds produced during their displays (Figure 3) and their signal-noise contrast scores were strikingly similar. Not only that, but their scores indicate that the signals from both species are highly effective in the context of the plant environment. These results demonstrate similar adaptations to their shared environment, while maintaining species recognition cues through morphology and overall display appearance.
The military mallee dragon (Ctenophorus fordi) and the painted dragon (Ctenophorus pictus) are very common in arid and semiarid sandy areas of northwest Victoria, South Australia, and southwest Queensland. We recorded displays at Ngarkat Conservation Park in South Australia, where they are often found in sympatry. These two species are much closer in appearance, but their display complexity and motor pattern use were just as contrasting as in the previous pair of lizards (Figure 2). In addition, the speeds produced during their displays and their signal-noise contrast scores were considerably higher in the painted dragon (Figure 3). We suggest this difference is related to the lack of territoriality in mallee dragons. This species is not known to protect territories or perform aggressive displays, so the motivation to produce conspicuous signals is likely to be reduced compare to its territorial relatives.
In this study we were able to show that the ring-tailed and long-nosed dragon perform displays with almost identical motion speed distributions and signal-noise contrast scores, despite utilising very different territorial displays (see Ramos & Peters 2017b for more details). In the case of the other sympatric pair, motion speed distributions and signal-noise contrast scores appeared to be much higher in the painted dragon than in the non-territorial mallee dragon. This difference in social behaviour could be key to explaining why the signals of the sympatric C. caudicinctus and G. longirostris seem equally well adapted to their local environmental noise, as evidenced by their equally high signal-noise contrast scores, but the signals produced by C. fordi and C. pictus do not. Thus, the selective pressure to generate signals with high efficacy appears to be mediated by signal function, at least in this context.
For the past eight years, my lab has conducted intensive research on green anoles (Anolis carolinensis) in Palmetto State Park in Luling, Texas, about an hour east of San Antonio. This park is beautiful – it’s centered around a swampy area dominated by dwarf palmettos (Sabal minor), and the San Marcos River flows through it. We’ve marked lizards and mapped their home ranges, watched their behavior, measured their morphology and parasite loads, and so much more. In past years, we’ve calculated that the density of green anoles in the park is approximately 0.04 lizards/m2, or about four adult lizards in every 10m x 10m area. We could regularly get sample sizes of around 150 lizards for behavioral studies in the park, but we very rarely collected animals from the park – we left them where we found them!
But this year is different. On three field trips to the park this summer, we have found very few green anoles. On our first visit this year in May, we spent 16 person-hours searching for lizards and found four green anoles. On our second visit in early June, we spent 14 person-hours searching and found eight. Last week, we spent another 12 person-hours and found only two. We see green anoles all over the city of San Antonio, and the students in my team are all skilled lizard spotters and catchers, so this isn’t due to inexperience. Also, we see other species of lizards all over the park – most commonly, Texas spiny lizards, little brown skinks, and house geckos– as well as garter snakes, copperheads, and cottonmouths. We also see tons of frogs.
So what happened to the anoles? We’ve considered a number of possibilities. The first thing we thought of was the possibility of feral cats – but we haven’t seen any cats in the park, and we think cats should have the same effect on the other herp species. What if the insect population had crashed? But again, that would affect the other lizards, snakes, and frogs too. This isn’t a year of particular drought or excess rain (and in previous wet and dry years, we’ve still seen lots of anoles), and the vegetation throughout the park largely looks the same as it has in the past. Perhaps an anole-specific disease has spread through this population?
In any case, the paucity of anoles in the park this year suggests that there won’t be many next year either, as there’s almost no one around laying eggs. It’s a bummer, because we’ve had such success here in the past.
Any ideas to explain this, AA readers?
Work we’ve published from our previous research in Palmetto State Park:
- Dill, A.K., T.J. Sanger, A.C. Battles and M.A. Johnson. 2013. Sexual dimorphisms in habitat-specific morphology and behavior in the green anole lizard. Journal of Zoology 290: 135-142.
- Battles, A.C., T.K. Whittle, C.M. Stehle, and M.A. Johnson. 2013. Effects of human land use on prey availability and body condition in the green anole lizard, Anolis carolinensis. Herpetological Conservation and Biology 8: 16-26.
- Bush, J.M., M.M. Quinn, E.C. Balreira, and M.A. Johnson. 2016. How do lizards determine dominance? Applying ranking algorithms to animal social behavior. Animal Behaviour 118: 65-74.
- Stehle, C.M., A.C. Battles, M.N. Sparks, and M.A. Johnson. In revision. Prey availability affects territory size, but not territorial display behavior, in green anole lizards. Acta Oecologica.
Late Breaking: one last Evolution 2017 post! Last weekend during the Evolution meeting, I had a chance to chat with Iris Holmes (Ph.D. student, University of Michigan) about the poster she presented. Initially not on our watch list because of the lack of “anole” in the description, my eye caught the dewlapping lizard perched at the top of her poster from across the room.
Iris presented her work on gut microbiomes of two groups of lizards: anoles and ameivas. She wanted to know if different taxa have different gut microbiomes and to what extent diet influences bacterial composition of gut microbiomes. Her collaborator (Ivan Monagan) collected scat samples from 22 Anolis dollfusianus and 9 Ameiva from an agricultural area in the Soconosco region of Chiapas, Mexico. Together, they then sequenced both the gut bacteria and the digesting prey with two 16S primers. Iris chose to target the prey as well because she wanted to know if they were eating different things and how different stages of digestion influence gut bacteria communities.
Iris found that there were no clear differences between the gut microbiomes of anoles and ameivas. Both species had gut microbiomes dominated by three main phyla: Proteobacteria, Firmicutes, and Bacteroidetes. Little is currently known about how these bacteria relate to digestion and health in reptiles, but Iris commented that we can make some guesses based on studies in other taxa. Proteobacteria are a disease indicator in mammals, but appear to be normal in reptiles and birds. Firmicutes and Bacteroidetes are both important for digestion of carbohydrates and fats (respectively) in mammals. Iris found that there was a loose correlation between the amount of prey consumed and the abundance of Bacteroidetes, suggesting these bacteria also play a role in digestion in lizards. She also found that there was an apparent tradeoff between the Proteobacteria and the two other groups – sequence abundance of proteobacteria was negatively correlated with abundance of Bacteroidetes and Firmicutes. Overall, this is an interesting first step in understanding the gut microbiomes of reptiles and how they differ (or don’t) between groups.
I’m hoping that some of you out there have been collecting Basal Metabolic Rate or Resting Metabolic Rate data on Caribbean anoles!
I’m working with a group of scientists on a large-scale comparative database on circulating hormones in free-living vertebrates – we call our collaboration HormoneBase – and we’re hoping to look at relationships between hormone levels and metabolism. (We’ll be presenting some of this work at the Society of Integrative and Comparative Biology meeting in January 2018 – check out our symposium announcement here!) We have a good list of anole species in the database, thanks to the work of Jerry Husak and Matt Lovern (2014), but it seems that very little metabolism rate data are available for these species. Do you know of such data, or do you have them – published or unpublished? If so, please contact me (firstname.lastname@example.org)!
Husak JF and MB Lovern. 2014. Variation in steroid hormone levels among Caribbean Anolis lizards: endocrine system convergence? Hormones and Behavior 65:408-415.
The knowledge of the past squamate fauna of the Guadeloupe islands (French Lesser Antilles) dramatically increased these last years in the framework of two European paleontological research programs. New archaeological and paleontological excavations (about which I previously talked) have been conducted and led to the discovery of thousands of squamate remains allowing to complete the pioneering works conducted by G. K. Pregill in the 90’s (Pregill et al., 1994). Results obtained on iguanas (Bochaton et al., 2016b), galliwasps (Bochaton et al., 2016a), ameivas (Bochaton et al., 2017a) and other taxa (Bailon et al., 2015; Bochaton et al., 2015; Boudadi-Maligne et al., 2016) point to high extirpation and extinction rates, mainly taking place during the last centuries after the European colonization of the archipelago and probably in relation to introduction of exogenous competitors and predators, as well as the practice of intensive agriculture.
In the middle of all of these extinctions, anoles, which are still very common in Guadeloupe, appeared to be kind of indestructible and were apparently not impacted at all by recent anthropogenic disturbances. However, the study of a huge assemblage of anole remains from Marie-Galante Island dated from Late Pleistocene to the 14th century reveals that this first impression was far from true.
Nearly 30,000 anole remains coming from several deposits were investigated using a combination of morphological and morphometric approaches. Size estimations (see Bochaton, 2016; Bochaton and Kemp, 2017) indicate that whatever the stratigraphic layer they come from, fully mature individuals range in three groups of Snout-Vent Length (SVL) size (Figure 2).
This analysis reveals a strong heterogeneity of the morphology of the dentary mostly depending of their size (allometry). The three fossil size groups are however closer to modern A. ferreus than to any other modern taxa and are linked by a common allometric relationship between their size and shape which differs from modern A. ferreus. The morphological variability of the fossil dentaries is also higher than that of modern A. ferreus (Figure 3).
These results indicate that all fossils are likely to correspond to A. ferreus. However, fossil representatives are more morphologically variable in terms of size, shape, and allometry than modern A. ferreus.The morphology of fossil A. ferreus remained stable during more than 30,000 years before an abrupt change that occurred during the last centuries. There is, however, a void of fossil data during the modern period which precludes linking this reduction of morphological variability between fossil and modern A. ferreus to a distinct event. Yet, this phenomenon is contemporaneous to the numerous extinction events documented on Marie-Galante and is thus very likely to be also related to the anthropization of the island.
This study also provides a strong argument again the hypothesis of the past occurrence of a second anole species smaller than modern A. ferreus on Marie-Galante and used to explain the large size reached nowadays by this insular solitary anole.
More details can be found in the publication of this work:
Bochaton, C., S. Bailon, A. Herrel, S. Grouard, I. Ineich, A. Tresset, and R. Cornette. 2017b. Human impacts reduce morphological diversity in an insular species of lizard. Proc. R. Soc. B 284:20170921.
Bailon, S., C. Bochaton, and A. Lenoble. 2015. New data on Pleistocene and Holocene herpetofauna of Marie-Galante (Blanchard Cave, Guadeloupe Islands, French West Indies): Insular faunal turnover and human impact. Quaternary Science Reviews 128:127–137.
Bochaton, C. 2016. Describing archaeological Iguana Laurenti, 1768 (Squamata: Iguanidae) populations: size and skeletal maturity. International Journal of Osteoarchaeology 26:716–724.
Bochaton, C., and M. E. Kemp. 2017. Reconstructing the body sizes of Quaternary lizards using Pholidoscelis Fitzinger, 1843 and Anolis Daudin, 1802 as case studies. Journal of Vertebrate Paleontology 37:e1239626.
Bochaton, C., R. Boistel, F. Cassagrande, S. Grouard, and S. Bailon. 2016a. A fossil Diploglossus (Squamata, Anguidae) lizard from Basse-Terre and Grande-Terre islands (Guadeloupe, French West-Indies). Scientific Report 28475:1–12.
Bochaton, C., S. Grouard, R. Cornette, I. Ineich, A. Tresset, and S. Bailon. 2015. Fossil and subfossil herpetofauna from Cadet 2 Cave (Marie-Galante, Guadeloupe Islands, F. W. I.): Evolution of an insular herpetofauna since the Late Pleistocene. Comptes Rendus Palévol 14:101–110.
Bochaton, C., S. Bailon, I. Ineich, M. Breuil, A. Tresset, and S. Grouard. 2016b. From a thriving past to an uncertain future: Zooarchaeological evidence of two millennia of human impact on a large emblematic lizard (Iguana delicatissima) on the Guadeloupe Islands (French West Indies). Quaternary Science Reviews 150:172–183.
Bochaton, C., R. Boistel, S. Grouard, I. Ineich, A. Tresset, and S. Bailon. 2017a. Evolution, diversity and interactions with past human populations of recently extinct Pholidoscelis lizards (Squamata: Teiidae) from the Guadeloupe Islands (French West-Indies). Historical Biology.
Boudadi-Maligne, M., S. Bailon, C. Bochaton, F. Cassagrande, S. Grouard, N. Serrand, and A. Lenoble. 2016. Evidence for historical human-induced extinctions of vertebrate species on La Désirade (French West Indies). Quaternary Research 85:54–65.
Pregill, G. K., D. W. Steadman, and D. R. Watters. 1994. Late Quaternary vertebrate faunas of the Lesser Antilles: historical components of Caribbean biogeography. Bulletin of Carnegie Museum of Natural History 30:1–51.
Major Anole Annals contributor Martha Muñoz gave a brilliant talk at the Evolution meeting as an awardee of a well-deserved ‘Young Investigator’ award from the American Society of Naturalists. In her talk, Muñoz discussed how two classic papers by Janzen (1967) and Huey et al. (2003) influenced the way she thinks about the interplay between behavior, physiology, and evolution. Not surprisingly, Anolis lizards played a leading role in her exposition.
Martha’s talk, entitled “Janzen’s hypothesis meets the Bogert effect: a synthesis nearly 100 years in the making”, started by describing Janzen’s hypothesis. In short, Janzen (1967) predicted that physiological differences among populations across altitudinal bands would be stronger in tropical mountains than in temperate ones. The main argument was that populations can more easily adapt to a given temperature range in tropical environments because these ranges are stable throughout the year, whereas the temperatures of different altitudinal bands overlap more in temperate areas due to seasonal variation.
Expanding on Janzen’s idea, Muñoz hypothesized that diurnal and nocturnal temperature variation in a single tropical mountain could also generate differences in physiological divergence among lowland and highland populations. The idea was that daytime temperatures were variable with overlap across elevation (similar to the seasonal picture in temperate areas) and nighttime temperatures were more constant and differed between elevations (similar to the seasonal picture in tropical areas).
To test this, Martha sampled populations in the Dominican Republic at sites ranging in elevation from sea level to 2400m. She then analyzed heat and cold tolerance of several species of anoles from the Anolis cybotes group. Results on cold tolerance (CT min) seem to agree with Janzen’s hypothesis: cold tolerance strongly covaries with altitude at night, with higher elevation populations having lower critical thermal minimums. Interestingly, however, heat tolerance (measured as CT max) was not at all associated with elevation.
Why did Janzen’s hypothesis fail to explain the evolution of heat tolerance across the altitudinal range? This question led to a key point of Muñoz’s talk: Janzen’s hypothesis might fail to predict evolution of CT max because it is agnostic about behavior. In the case of ‘cybotoid’ anoles, lizards from different altitudes could actively adjust their habitat use to achieve optimal temperatures. As a consequence, thermoregulatory behavior could forestall evolution of physiology in heat tolerance. By studying habitat use across different elevations, Muñoz showed that, although anoles behave as thermo-conformers at low elevations, they clearly thermoregulate at high elevations. In other words, anoles were at similar temperatures to the average available substrates in lowlands but their body temperatures were significantly higher than perches at higher elevation.
This was at least partially explained by habitat use differences: anoles at high elevations perched most frequently on boulders, which are on average about 5º C warmer than trees –the most used substrate in low altitudes. In fact, 90% of the trees Martha sampled at these high elevation sites were lower in temperature than the preferred temperature of the lizards! These data indicate that anoles from the A. cybotes group have buffered natural selection in physiology by means of behavioral adjustments –a phenomenon known as the Bogert effect (also called behavioral inertia; Bogert 1949).
Finally, the talk had a third part. And yes, it got even more interesting! Due to the observed habitat use differences in high latitudes, Muñoz and her collaborators predicted that although behavior could buffer physiological evolution on heat tolerance, it could spur evolutionary change in ecologically-relevant morphological traits (the behavioral drive hypothesis). Specifically, they predicted that increased use of boulders (for thermoregulation) at high elevations should drive morphological shifts in traits related to boulder use: head and limb morphology. They found evidence for these hypothesized morphological differences: high elevation lizards had higher head heights and longer hindlimb, in agreement with functional predictions. Finally, a captive breeding experiment confirmed that these differences were the consequence of genetic changes and not simply due to developmental plasticity.
Martha’s research is a great example of how, as Huey said, studying behavior can be crucial to improve our understanding of evolutionary processes. We are looking forward to hear about future research from the Muñoz lab, which is about to open at Virginia Tech!
Muñoz, M.M., Losos, J.B. Thermoregulation simultaneously promotes and forestalls evolution in a tropical lizard. (Accepted pending minor revision). American Naturalist.
In his Masters thesis conducted in Simon Lailvaux’s lab at the University of New Orleans and presented this week at Evolution 2017, David Weber used a multiyear data set of Anolis carolinensis lizards’ locations and morphology as well as a DNA-based pedigree to investigate the effects of body size and relatedness on the spatial distribution of these lizards. Specifically, he set out to test three hypotheses: first, are males’ home ranges larger than females’ home ranges? Second, are bigger males more likely to be surrounded by smaller males that are related to them? And third, is there any evidence for the inheritance of home ranges from parent to offspring?
Lizard locations were sampled in an urban New Orleans park twice a year, in the fall and in the spring, from 2010 to 2015. The dataset included over 800 individuals, and what struck me most about these data was that, of these 800+ individuals, fewer than 100 were observed often enough to estimate home range volumes–death and dispersal can rule these lizards’ lives! Male and female home range volumes did not differ significantly (and the trend was in the direction of females moving over larger areas, which concurs with data from Robert Gordon’s 1956 thesis on green anoles, but with little else, I think). Curiously, smaller neighbours of the biggest males were less related to them than were males found farther away, suggesting that male anoles don’t preferentially tolerate their kin over non-kin. And though philopatry (aka site fidelity aka staying the same place) was rare overall, females were a bit more likely to co-occur with their male offspring than males were. In a result that conforms to traditional wisdom, Weber found that the biggest males in the site seemed to avoid each other, potentially spacing themselves as far apart as possible.
Following a kind shout-out to my and Jonathan Losos’ recent paper on Anolis territoriality or the lack thereof, Weber chose to interpret his results as making sense only outside of a territorial framework. Unsurprisingly, I concur with this decision entirely, and am excited to see where Weber goes with this idea in the publications resulting from this mammoth dataset!
The arrival of an outsider that overlaps in resource use and habitat with local species can lead to intense competition between the two. A result of this competition can be character displacement, where traits of the species (one or both) change in sympatric populations (where the co-occur), but not in allopatric populations. Claire Dufour (Post-Doctoral researcher at Harvard University) presented her work on character displacement for two anole species on the island of Dominica: the native Anolis oculatus and the introduced Anolis cristatellus. Her objective was to integrate ecological, antagonistic and reproductive character displacement. Specifically, she tested whether competition between these new island-mates leads to changes in habitat use, morphology, and display behavior.
Claire compared allopatric populations of the two species with sympatric populations in the northern area of the island in Calibishie, where Anolis cristatellus has been present for two years. She found that in sympatry, both morphological and behavioral shifts have occurred. In sympatry, Anolis oculatus perched higher and had shorter limbs. She also found differences in display behavior, which she tested with an anole robot programmed to dewlap and do push-ups. This experiment showed that in sympatry, Anolis cristatellus dewlapped less, but Anolis oculatus does not alter its display behavior. Future work will test for reproductive character displacement and contrast populations where Anolis cristatellus has been present for a longer time span.
The Sensory Drive hypothesis predicts that species will evolve communication signals that are effective in the particular light environment in which they occur. Anolis lizards are an excellent example: in dark habitats, they tend to have light-colored, highly reflective (and transmissive) dewlaps that are usually yellow or white in color, whereas in bright, open environs, dewlaps tend toward blue, black, orange or red. However, demonstrating that these dewlaps are actually effective at being visible in their particular habitats has proven surprisingly challenging.
Leo Fleishman has been a leader in this area and in a talk at the sensory ecology symposium at the evolution meetings, he presented new and exciting developments. First, in line with previous work, he showed that the spectral reflectance/transmittance of dewlaps is not particularly well-matched to that of the background. Rather, the same colored dewlaps appear to be maximally contrasting with the radiance of the background across all habitats: basically all habitats have mostly green backgrounds, and red or orange stands out the best against the green background, no matter what the habitat. So much for sensory drive, it would seem!
But more recent work saves the day: it turns out that habitats differ in the total intensity of light (number of photons coming down) they receive and that, furthermore, across species, dewlap intensity (total photons reflected and/or transmitted) is negatively related to habitat intensity (with one notable outlier, the enigmatic A. gundlachi). Under the relatively low light conditions of forest shade or partial shade, color discrimination becomes more difficult, and colors such as red and orange and other dark colors do not stand out well against the background, because they simply do not emit enough photons to efficiently drive color vision. Yellow or white works better. Conversely, in intense light environments, there is enough light to easily see the darker colors, and these stand out well against the green background. Moreover, behavioral experiments confirm that in bright light conditions red stimuli are most visible against a green background, whereas in low light yellow stimuli are more visible. Thus, even though most Anolis habitats have similar spectral properties, differences in total light intensity strongly influence what colors are most effective, and thus appear to have played a major role in the shaping the evolution of dewlap colors.