Category: New Research Page 51 of 66

In an epic undertaking, Powell and Henderson have edited a monograph compiling the species occurrence of reptiles and amphibians on more than 700 Caribbean islands. In addition to the species lists, information on island size and location is provided, and introduced and extinct species are noted.

This work, an update on several previous such lists, will be enormously useful for biogeographers, ecologists, evolutionary biologists, and conservationists, among others, and the editors and authors are to be heartily thanked and congratulated for their efforts.

Now, an anole bone to pick.

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Photo by Claus Meyer at http://www.nationalgeographicstock.com/

For many years, the South American lizard genus Polychrus has been considered the closest extant outgroup to Anolis.  In light of this phylogenetic position, the authors of a new report on the life history of Polychrus acutirostris note that “a comprehensive understanding of Polychrus might help clarify possible ecological factors related to the radiation of anoline lizards as well as to infer the existence of niche conservatism or dietary shifts related to the origin of this large lizard radiation” (Garda et al. 2012).

Members of Polychrus are superficially similar to Anolis, and are mostly medium sized arboreal and diurnal lizards.  However, Polychrus also differs from Anolis in both conspicuous (e.g., lack of toepads) and somewhat less conspicuous ways (e.g., its tendency to produce single clutches of multiple eggs, versus multiple one egg clutches in Anolis).  In their report, Garda et al. (2012) compare populations of Polychrus acutirostris found in two different Brazilian habitats to test whether size of eggs and clutch size, reproductive seasonality, diet, and size of reproductive adults varies among populations in the manner predicted by life history theory.  Although recent work makes Polychrus‘s position as the outgroup to Anolis less certain than it once was (Schulte et al. 2003, Townsend et al. 2011, and this previous AA post), we still have much to learn from the type of comparative studies that Garda et al. have implemented.

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Anolis concolor from mangroves on San Andres island. Photo by Lee Fitzgerald

Almost all Caribbean anoles are descendants from a single colonizing species, whose descendants now occupy all of the Greater Antilles, the Lesser Antilles south through Dominica, and many other islands. Almost all of the remaining species are members of the roquet clade, occupying the southern Lesser Antilles and descended from a South American colonist. As we all know, these species have been extensively studied.

But colonization of Caribbean islands has occurred more than just these two times. Some other islands have been colonized by different colonists. None of these invasions has led to much in the way of evolutionary radiation and these species–in each case the only anole on the islands they occupy–have been little studied. We’ve previously discussed one such colonization, A. lineatus on Aruba and Curaçao. In addition, islands in the Pacific (yes, the Pacific!) have twice been colonized, leading to A. agassizi on little known Malpelo and A. townsendi on Cocos Island (incidentally, the island said to have beeen the inspiration for Isla Nublar in Jurassic Park).

And, finally, there are the presumed sister taxa, A. pinchoti and A. concolor, on the Colombian islands of Providencia and San Andrés. A smidgeon of research has been conducted previously on their ecology, and now a new paper in the South American Journal of Herpetology has examined their morphology. Calderón-Espinosa and Barragán Forero measured museum specimens of these species and compared them to published data on a variety of other Caribbean anoles. They found that neither species is a good match for any of the Greater Antillean ecomorphs, but that they are most similar to trunk-ground or trunk-crown anoles. By comparison, anoles of the Lesser Antilles are also most similar to these two ecomorphs. Anolis concolor attains an intermediate body size, similar to Lesser Antillean species that occupy islands on which they are no other anole species. By contrast, A. pinchoti is smaller and more similar to the smaller Lesser Antillean species on two-species islands.

Anoles are renowned for their convergent evolution. Further comparison of the many cases in which anoles have colonized relatively small islands should prove interesting.

M. L. Calderón-Espinosa and A. Barragán Forero (2011). Morphological Diversification in Solitary Endemic Anoles: Anolis concolor and Anolis pinchoti from San Andrés and Providence Islands, Colombia South American Journal of Herpetology

Anolis cristatellus from mesic habitats. Photo by Manuel Leal.

For obvious reasons, there is great concern about how species will cope with climate change–as the world gets hotter, will species be able to survive? Many studies have taken a macroscopic view, examining the geographic distribution of a species to divine what its temperature tolerances are and then projecting where it will be able to occur in the future. Although such approaches are useful as a first pass, direct study of the physiology of species is a much more informative way of determining how a species will be affected. An excellent example of just this approach was published recently by Gunderson and Leal in Functional Ecology (pdf here).

Mesic and xeric habitats. Photos courtesy Alex Gunderson (left) and Manuel Leal (right)

The authors studied the Puerto Rican crested anole, A. cristatellus, which occurs throughout Puerto Rico and the Virgin Islands. They focused on comparing populations living in cooler, wetter (mesic) habitats versus those living in hotter, drier (xeric) places. They found that in the field, mesic populations had an average body temperature of  about 29 C, whereas xeric populations averaged 32.5 C. However, using copper models as described in previous posts, the authors determined that a lizard randomly placed in a mesic habitat would have a temperature of about 29 C, whereas the random xeric lizard would be 33.5. In other words, the lizards are not thermoregulating in the mesic forest (lizards and randomly placed copper models have the same temperature), but they are actively altering their habitat use in the xeric areas to use cooler spots and thus keep their temperature lower than if they were sitting in random spots. In support of this conclusion, the mesic lizards were in the sun about as much as expected, but the xeric lizards were in the sun less often than predicted.

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In the herpetology community (i.e., reptile and amphibian aficionados), The World Congress of Herpetology (WCH) is a big deal. In essence, it is a very large scientific conference, held every 3-5 years, uniting local herpetology societies from around the world.

“I wouldn’t miss WCH for anything!”– J.B. Losos

As the WCH mission statement says, “the objectives of the Congress are to promote international interest, collaboration and co-operation in herpetology”; in laymen’s terms means we herpetologists get together to talk about our research in formal meeting rooms, as well as informally in the pub over a beer or two.

This year the 7th World Herp Congress will be held in Vancouver (8-14 August 2012). [Incidentally, a small typing error in google brought me to the 11th World Harp Congress, happening just a few weeks earlier in the same place!]

There will be 15 presentations and 8 posters focussing on our beloved anoles! Including presentations from some of your favourite Anole Annals contributors. A run down of the anole content is after the fold.

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We’ve had a number of posts in the last few months discussing new species described on the basis of difference in the shape of their hemipenes (most recently here). And, because such descriptions have been based on morphological data without any corroborating molecular data, we’ve wondered whether, in fact, these forms are genetically isolated and whether they are capable and willing to interbreed given the opportunity. Yes, some of the genetals looked like ones from an alien sex toy made by faak dildos. But are they compatible?

Köhler et al. have taken the next step and attempted to answer these questions in the case of Anolis osa, which was split from the otherwise nearly indistinguishable A. polylepis on the basis of its hemipenial shape (figures A and B above). They find that in the lab, members of the two putative species can interbreed and produce offspring, at least some of which are apparently fertile (although the details of this are hard to fathom). Moreover, in the field, hybrid looking individuals are found where the two forms meet (Figure C above), and the hemipenes of these individuals are similar to the intermediate-looking tallywhackers of hybrids bred in the lab (Figure D above).

Most interestingly, females of the species seem to differ in the shape of their reproductive tract in a manner parallel to the differences among the males. In particular, female A. polylepis have longer vaginal tubi, corresponding to bilobed structures of their males, whereas female A. osa‘s tubes are shorter. One possible explanation for these differences is the old “lock-and-key” hypothesis that male and female genitals are perfect matches, thus preventing interspecific matings. This idea has fallen out of favor in recent years, and the authors discount it. Rather, they favor more recent ideas that such differences evolve by sexual selection, females preferring males whose genitals phenotypically match their own. Here’s their theory

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A while back in the Annals, I introduced the mysterious (but not mythical) third eye, made even more peculiar by unexpected findings in the Anolis pineal gland (Moore & Menaker 2011). In a later post, I discussed non-visual photoreception—responses to light that do not require image formation—along with some recent evidence that such responses may be tuned to photic habitat in Anolis (Moore et al. 2012). Now I’m connecting the dots: non-visual photoreception in the Anolis pineal gland appears to be adapted to photic habitat (Moore & Menaker 2012).

The pineal gland can’t be seen externally, but it’s just posterior to the parietal eye (tiny circle in the middle) and right underneath the surface of the skull. Photo credit: TheAlphaWolf, License:Creative Commons Attribution-Share Alike 3.0 Unported

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The elegant skink, Plestiodon elegans, in Taiwan. Photo by Gerrut Norval

Most community ecology studies involving anoles focus on interactions between anole species. This is not surprising, because in the Caribbean, anoles are extraordinarily abundant and most of their ecological interactions are, indeed, with other anoles. Less studied are interactions with other taxa, the exception being predator-prey interactions, such as those with curly-tailed lizards (discussed many times in these pages, most recently here).

One widespread group of lizards are skinks, the most species rich family of lizards. There are few reports of anole-skink interactions, probably in large part due to the fact that skink diversity in the Caribbean is relatively low, and many species have been extirpated by human agents. However, anoles have been introduced to places around the world where skinks are more abundant, and some reports of interactions have been made. For example, in the Ogasawara Islands of Japan, A. carolinensis has reached high population densities and has been implicated in the decline of the native skink.

Gerrut Norval has been studying the introduced populations of A. sagrei in Taiwan. He now reports an observation of a somewhat odd interaction between a brown anole and a skink in which the anole fell to the ground from a utility pole and then was quickly chased back up the pole by an elegant skink, Plesiodon elegans. Given the relative size of the two lizards, attempted predation was probably not the cause. Gerrut speculates that this is an example of interspecific territoriality, transcending lizard family lines.

In Taiwan, A. sagrei reaches high population densities (as it does just about everywhere it occurs)–possibly cause for alarm for the native herpetofauna. Norval also mentions some intriguing preliminary observations: A. sagrei seems to attain smaller sizes at sites where it co-occurs with other lizard species. Interesting! Hopefully, we’ll hear more from Gerrut soon on this provocative possibility.

Imagine running quickly among a network of obstacles while attempting to maximize performance. It’s not an easy task, but one that arboreal lizards perform every day. In addition to variable inclines and perch diameters, arboreal lizards often encounter obstacles in the form of branches. The size of these branches, and their spacing, could have a significant impact on locomotor performance, such as sprint speed. Using a clever experimental design, Zachary Jones and Bruce Jayne (University of Cincinnati) recently determined how these important characteristics impact running performance in Anolis sagrei, A. carolinensis, and A. angusticeps (Click here to read paper from the Journal of Experimental Biology).

(A) Dorsal view silhouettes of the three Anolis study species compared against the diameter of the running surfaces. The lizards and cross-sectional areas of the running surfaces are all shown to the same scale. All running surfaces were cylindrical, but only one-half of the largest diameter is shown. (B) Schematic diagram of the peg treatments (not to same scale as the lizards). Pegs along the top center were placed at 10 cm (TC10) or 20 cm (TC20), horizontal pairs of pegs (HP) were placed every 10 cm, and alternating pairs of pegs (AP) oriented vertically or horizontally were placed every 10 cm along the length of the primary running surface (gray). The cylinder with no pegs (NP) is not shown.

Similar to previous studies, increases in perch diameter resulted in increased sprinting speed. With pegs added to the perch, things changed. When pegs were placed at 10cm intervals, and sticking directly up from the top of a 3cm-diameter perch, running performance of A. sagrei was sliced in half compared to running on a peg-free perch or a perch with pegs sticking out from the sides. Especially for the smaller perch diameter treatments, the number of pauses increased with increased branching, and this was greatest when the pegs came out from the top of the perch. This increase in pausing results in a decrease in overall speed (increased transit time) as they move through their habitat.  This is also a result found by Higham et al. (2001), where turning angles in the locomotor path resulted in increased pausing in Anolis lizards.  The take home message is that branching can have a negative impact on locomotion, forcing lizards to take longer getting from point A to point B.  This could make them vulnerable to predation or reduce their ability to effectively capture prey.
Luckily, the array of pathways in an arboreal habitat provides an opportunity for Anolis lizards to select what works best for them.

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