Category: New Research Page 41 of 66

Over at The Lizard lab, Martin Whiting discusses a recent paper published in Biological Conservation on the conservation status of reptiles. Basically, a cast of thousands assessed a random sample of 16% of the world’s reptile species, categorizing them into the IUCN’s categories of conservation concern, which range from “least concerned” to “critically endangered” and, of course, “extinct.”

Martin nicely summarizes the paper in his post, but I’ll reprint his conclusion summary paragraph here: “59% of species were Least Concern, 5% were Near Threatened, 15% Threatened (Vulnerable, Endangered or Critically Endangered) and 21% were Data Deficient. To put this another way, one in five species are threatened with extinction and another one in five are data deficient. The paper identifies freshwater habitats, oceanic islands and tropical regions as containing the highest proportion of threatened species. Habitat loss and direct harvesting are two key threats to reptile populations and these are depicted in Figure 3 from the paper” (above).

Of course, from the AA perspective, the question is: what about anoles? The results were, to me at least, surprising. Of the 65 species surveyed, 29.3% were in one the three threatened categories, nearly twice as many as the global average! I would have guessed the opposite–most anoles seem to being doing reasonably well. But, then I rationalized, it must be the mainland anoles, because Caribbean anoles are generally doing fine. Again wrong! 11/28 (39%) Caribbean anoles are in these categories (including the only two “critically endangered species, A. juangundlachi (known from one specimen, if I recall correctly) and A. roosevelti), compared to 8/37 (22%) for mainland species. One non-surprise is that all 10 “data deficient” species are from the mainland; however, even when they are removed, the percentage threatened in the mainland (30%) is still less than in the Caribbean. At least for the Caribbean species, the biggest predictor seems to be range size, as all threatened species either have small distributions or occur on small islands. I am less familiar with some of the mainland species, but think the same may be true for those. I’ll append the list below.

One last note: the paper truly has an extraordinary number of authors who contributed to this massive compilation. One amusing consequence is that the list of authors’ affiliations at the start of the paper is three pages long!

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Based on a long-standing program of field exploration initiated by the Smithsonian’s National Museum of Natural History and the University of Guyana, with further support from the American Museum of Natural History and the Royal Ontario Museum, a distinguished cast of authors, each with extensive experience in Guyana, has just published this enormous and useful monograph. Part of the abstract is appended below, but more importantly you may be wondering, just which anoles occur in Guyana? The answer is that there are at least five native species (auratus, fuscoauratus, ortonii, planiceps, and punctatus). They note, as well, that chrysolepis is reported to occur in Guyana as well, but all chrysolepis group specimens they examined turned out to be planiceps.

In addition, at least one Lesser Antillean species occurs in the cities of Georgetown and Kartabo. These invaders have been identified as both A. extremus from Barbados or A. aeneus from Grenada and the Grenadines, but the authors were unable to find any reliable morphological characters that could distinguish the two species, and thus could come to no conclusion about which species, or both, occur in several cities in Guyana, though they did note that Ernest Williams had identified many of the specimens in museums from Guyana as A. aeneus, as good a reason as any to attribute them to that species. The authors conclude “Clearly, the taxonomic status of Anolis aeneus versus Anolis extremus needs further investigation, both in areas where they occur in the West Indies and where they have been introduced on islands and the mainland of South America.”

Honorary anole friend Polychrus marmoratus also occurs in Guyana and is pictured above.

The first half of the two-page abstract:

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The most recent issue of Herpetological Review (December 2012) includes an article by Ted Townsend, “Proposal to Alter Anole Taxonomy and Ecological Nomenclature.” Townsend does an admirable job of summarizing the issues and, most importantly, includes a shout out to Anole Annals (“an internet forum frequented by anole researchers”). Also notable is the wacky photo that appears to the left of the article (and the left of this text).

Figure 3 from Helmus and Ives (2012)

For 50 years, scientists have been cataloguing the relationship between area of islands or other patches of habitat and the number of species they contain. In general, the bigger the area, the greater the number of species. In recent years with the rise of interest in incorporating a phylogenetic perspective to all manner of questions, some have wondered how the phylogenetic variety (the degree of relatedness among species) changes with area. In an important new paper, Helmus and Ives take a theoretical perspective to understand what the expectation is for the relationship between phylogenetic diversity and area. Most excitingly, they illustrate their method using data from anoles on Caribbean islands.

Here’s how they describe what they’ve found: “While there was a strong relationship between Anolis species richness and Caribbean island bank area (Fig.3A; Losos 1996, Losos and Schluter 2000), we found no overall relationship between Anolis phylogenetic diversity and island bank area (Fig. 3B) …The greatest variation in phylogenetic diversity was associated with the overall level of in situ speciation … [T]here is a strong PDAR for the seven Caribbean island banks with at least one in situ speciation event (Fig. 4A). The estimated phylogenetic diversity values of these seven banks are dominated by in situ speciation as opposed to among-island allopatric events (Cuba had 2, 47, 49 colonizations, in situ events, species richness, respectively; Hispaniola had 4, 33, 37; Puerto Rico had 3, 11, 14; Jamaica had 1, 5, 6; Guadeloupe had 1, 3, 4; Grenada had 1, 1, 2; and St. Vincent had 1, 1, 2). The strong Anolis SAR causes a strong positive PDAR for these banks because species richness and the number of in situ speciation events positively correlate (Figs. 3A and 4B). If island assemblages were only derived from in situ speciation, then, according to the neutral macroevolutionary model we used, phylogenetic diversity is expected to positively increase, and then plateau with the number of in situ speciation events (Fig. 4C), which is the same relationship we found for the seven island banks (Fig. 4B). On at least the four Greater Antilles islands, island area sets a limit to the number of Anolis species that can arise via in situ speciation (Rabosky and Glor 2010). Thus, when there are no external colonizations that add large amounts of external evolutionary history to island assemblages, positive PDARs are expected.

It is the balance of ancestral colonizations to in situ speciation, therefore, that affects regional phylogenetic diversity. This balance is thought to be determined by a race between colonists, where initial colonist species will diversify if another colonist species does not arrive and establish too soon after the initial colonization event (Gillespie 2004). For Anolis, this balance is related to island area, the timing of island emergence and species diversification, and island isolation (Losos 2009). For example, the largest island bank, Cuba, is the center of Caribbean Anolis diversity and was likely colonized twice, by the ancestor of most Caribbean Anolis, and possibly to all Anolis (Nicholson et al. 2005), and more recently by a colonist species from Hispaniola, whose ancestor was originally Cuban (Mahler et al. 2010). Cuba thus contains a large amount of phylogenetic diversity, not because it has received outside colonists, but because it is large in area and contains old diverse lineages that have arisen via in situ speciation. Small and spatially isolated banks such as those in the lower Lesser Antilles (e.g., Grenada) have had few ancestral colonizations and few in situ speciation events that together result in low phylogenetic diversity. In contrast, species assemblages on small and non-isolated banks (e.g., the Acklins bank of the Bahamas) are completely derived from among-island colonization’s, and thus, have high phylogenetic diversity similar to the Cuban bank (Fig. 3B). Macroevolutionary simulations should thus be extended to include these isolation effects. However, the model and the Anolis data suggest that, in general, PDARs should be flat for oceanic islands whose species assemblages are an outcome of both in situ speciation and multiple colonizations.”

Figure 4 from Helmus and Ives (2012).

Uta stansburiana mating. Image from http://cabezaprieta.org/

The side-blotched lizard, Uta stansburiana, is one of the most widely-studied lizard species, thanks largely to work by Barry Sinervo and colleagues on the evolution of  alternative mating strategies (a.k.a. the rock-paper-scissors game in lizards).  The most recent report on the evolution of this interesting species investigates reproductive isolation between two populations of Uta that diverged within the last 22,500 years.  One of these populations is found on lava flows and the others if found off the lava flows.  This report by Corl et al. (2012) is noteworthy because recent work on a range of other organisms suggests that some “rules” for the evolution of reproductive isolation are shared across the tree of life.  Do these rules also apply to lizards?

To my knowledge, patterns of reproductive isolation have only been investigated experimentally in one other genus of lizards: Lacerta (Rykena 1991, 1996; Olsson et al.  2004). This work with Lacerta suggest substantial intrinsic reproductive isolation between species resulting from low fertility and high rates of developmental defects in hybrid crosses. Studies of Lacerta also support Haldane’s Rule because females hybrids (ZW) suffer more fitness consequences than male hybrids (ZZ).

By conducting experimental hybridization studies between these two populations of Uta, Corl et al. (2012) were able to show that significant reproductive isolation has evolved between populations, largely in the form of pre-zygotic post-mating isolation; inter-population crosses produce significantly more unfertilized than fertilized eggs relative to intra-population crosses.  Corl et al.’s results are also consistent with at least one general rule for the evolution of reproductive isolation that has been reported in other organisms; asymmetric reproductive of isolation between the two Uta populations is consistent with Darwin’s Corollary to Haldane’s Rule.

How does all this relate to anoles?  My lab is interested in this work because we’re in the midst of a major project designed to answer questions about intrinsic reproductive isolation in Anolis.  Anthony Geneva reported on some preliminary results of this work earlier this year and we hope to have more to report sometime in the near future.

Rykena, S. 1991. Hybridization experiments as tests for species boundaries in the genus Lacerta sensu stricto. Mitteilungen aus dem Zoologischen Museum Berlin 67:55–68.

Rykena, S. 1996. Experimental interspecific hybridization in the genus Lacerta. Israel Journal of Zoology 42:171–184.

Get all the details in the newly posted paper by Eckalbar et al. in BMC Genomics “Genome reannotation of the lizard Anolis carolinensis based on 14 adult and embryonic deep transcriptions,” just posted on BMC Genomics. Here’s the low-down: “The green anole lizard, Anolis carolinensis, is a key species for both laboratory and field-based studies of evolutionary genetics, development, neurobiology, physiology, behavior, and ecology. As the first non-avian reptilian genome sequenced, A. carolinensis is also a prime reptilian model for comparison with other vertebrate genomes. The public databases of Ensembl and NCBI have provided a first generation gene annotation of the anole genome that relies primarily on sequence conservation with related species. A second generation annotation based on tissue-specific transcriptomes would provide a valuable resource for molecular studies. Here we provide an annotation of the A. carolinensis genome based on de novo assembly of deep transcriptomes of 14 adult and embryonic tissues. This revised annotation describes 59,373 transcripts, compared to 16,533 and 18,939 currently for Ensembl and NCBI, and 22,962 predicted protein-coding genes. A key improvement in this revised annotation is coverage of untranslated region (UTR) sequences, with 79% and 59% of transcripts containing 5′ and 3′ UTRs, respectively. Gaps in genome sequence from the current A. carolinensis build (Anocar2.0) are highlighted by our identification of 16,542 unmapped transcripts, representing 6,695 orthologues, with less than 70% genomic coverage. Incorporation of tissue-specific transcriptome sequence into the A. carolinensis genome annotation has markedly improved its utility for comparative and functional studies. Increased UTR coverage allows for more accurate predicted protein sequence and regulatory analysis. This revised annotation also provides an atlas of gene expression specific to adult and embryonic tissues.”

In recent years, a quirky area of research has developed in which researchers measure the length of the second and fourth digits on the hand and foot, calculate the ratio (2d:4d) and then compare this ratio between the sexes. Surprisingly, in many species there are consistent differences between males and females. In mammals, that ratio is smaller for males, whereas in birds, the opposite occurs. But few studies have looked at the other vertebrate classes.

With this in mind, Direnzo and Stynoski recently calculated digit ratios for several common Costa Rica anoles and frogs. The abstract of their paper, published in Anatomical Record last year, tells the story:

“It is now well documented that androgen and estrogen signaling during early development cause a sexual dimorphism in second-to-fourth digit length ratio (2D:4D). It is also well documented that males of mammalian species have a smaller 2D:4D than females. Although there are discrepancies among 2D:4D studies in birds, the consensus is that birds exhibit the opposite pattern with males having a larger 2D:4D than females. The literature currently lacks substantial information regarding the phylogenetic pattern of this trait in amphibians and reptiles. In this study, we examined 2D:4D in two species of frogs (Oophaga pumilio and Craugastor bransfordii) and two species of lizards (Anolis humilis and Anolis limifrons) to determine the existence and the pattern of the sexual dimorphism. Male O. pumilio and C. bransfordii displayed larger 2D:4D than females in at least one of their two forelimbs. Male A. humilis had larger 2D:4D than females in both hindlimbs, but smaller 2D:4D than females in both forelimbs. Male A. limifrons may also have smaller 2D:4D than females in the right forelimb. Finally, digit ratios were sometimes positively related to body length, suggesting allometric growth. Overall, our results support the existence of the 2D:4D sexual dimorphism in amphibians and lizards and add to the knowledge of 2D:4D trait patterning among tetrapods.”

Green anole, emerging on the experimental scene. Photo by Justin Walguarnery.

They really are small. Photo by Justin Walguarnery

In their rate of heating and cooling. A recent paper by Walguarnery et al. reveals that baby green and brown anoles change temperatures at a remarkably rapid rate, much higher than that reported for most other vertebrates and comparable to that of insects. The reason would seem to be obvious: they are small, with a large surface-to-volume ratio, and thus they gain and lose heat rapidly. Moreover, the typical lizard posture, with body resting on the substrate, enhances the rate of conductive transfer of heat.

Brown anoles, too. Photo by Justin Walguarnery

The authors point out that this finding has interesting implications for our understanding of habitat partitioning between species. In particular, if the body temperature of juvenile anoles very rapidly equilibrates with the operative environmental temperature of the exact spot they occupy, then individuals can very precisely regulate their body temperature, whereas the slower change of larger lizards makes it more difficult to finely adjust body temperatures by moving from one spot to another.

As part of the study, the authors also measured the preferred body temperature of lizards in laboratory gradients and found that juvenile green anoles preferred to be 2 degrees warmer than brown anoles. This result is particularly interesting because previous work on adult lizards had found that brown anoles prefer warmer temperatures. Assuming that this is a real effect and not an artifact of differences between the methodologies of the two studies, this finding raises interesting questions: why do temperature preferences change ontogenetically, and what implications do these changing preferences have for patterns of habitat partitioning? From my own personal experience, adult brown anoles usually appear to occur more frequently in hot and exposed positions than green anoles, and it hasn’t been obvious to me that the habitat use of juveniles of the species is any different, but I have to admit I haven’t paid that much attention to the little fellas. Like anole biology more generally, the thermal ecology of juvenile anoles is a little explored and potentially important area for future research.

But enough of my blathering. Let’s hear what the author, Justin Walguarnery, has to say about the paper:

“The study was conducted as part of a series of investigations into how two of the most widespread Anolis species interact early in life. In particular, we were interested in identifying patterns of behavior and physiological ecology present immediately after hatching. Our goal here was to observe species characteristics defining the fundamental niche that might be constrained, modified, or obscured later in life.

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AA contributor and anole breeder extraordinaire Veronika Holáňová and colleagues have just described a new species of Chamaeleolis, Anolis sierramaestrae, from–where else?–the Sierra Maestra of eastern Cuba. The species, described in a paper just published in Acta Societatis Zoologicae Bohemicae, differs in a variety of scalation details from the other five species in this group, and the paper includes a very useful pictorial guide to distinguishing among them.

In addition, check out this nifty x-ray.