Category: New Research Page 10 of 67

Evolution 2018: Sex Chromosome Evolution

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On September 4, 2018

In New Research

“Squamates  Playing Poker” – a clever depiction of sex chromosome evolution (image by Anna Minkina shared with permission from Tony Gamble; read more about the image on the Gamble lab website)

Anole Annals contributor Yann Bourgeois reports on the talk by Tony Gamble on sex chromosome evolution. While this talk wasn’t specifically about anoles, our favorite lizards are no stranger to this topic, as discussed previously here on Anole Annals. Gamble builds on his previous work in an impressive analysis of sex chromosome evolution across squamates and snakes. We can look past the anoles taking the back-seat on this one because the talk was fascinating and sure to be of interest to readers here. Yann Bourgeois reports:

How sex chromosomes originate is one of the most intriguing questions of evolutionary biology. It is also a complex one, as the mechanisms that lead to their formation are not clearly understood and our knowledge is mostly based on model species that are not necessarily representative (most of them have strongly heteromorphic sex chromosomes). It is generally thought that sex chromosomes emerge as new alleles at a sex-determining gene stop recombining with each other. Since sex-ratio has to reach an equilibrium, balancing selection maintains the two alleles at high frequencies, and strong linkage locks together loci involved in reproductive isolation and mating. As the two non-recombining blocks diverge they accumulate mutations that can be used to discriminate them using molecular tools. In the most extreme case, one of the two chromosomes degenerates, such as the Y chromosome in humans.

Most sex-determining systems fall into two categories: ZW systems where the male is homozygous ZZ and females are heterozygous, and the classical XY system with XY males and XX females. We know from previous research that anoles fall into the XX/XY category (although some species are XXXX/XXY).  However, in general in squamates and snakes in particular, the evolution of sex-chromosomes is poorly known. Early studies mostly focused on heteromorphic chromosomes, which are so divergent that they can easily be identified through cytogenetics. But heteromorphic sex chromosomes like those in anoles and other squamates are not necessarily visible, and other tools are needed to identify which system occurs in a given species.

In his talk, Gamble showed how to use RAD-seq or RNA-seq to identify loci associated with sex, and to discriminate between XY and ZW systems (for more information on this approach, check out his 2015 paper in Molecular Biology and Evolution). For example, in an XX system, all males will be heterozygous at sex-linked loci while all females will be homozygous at the same sites. Depth of coverage will also be twice as low at X-linked loci for males than for females as they harbor a single X chromosome. Using this set of molecular methods, Tony demonstrates that there is a high turn-over of sex-determining systems in squamates and snakes, with more than 40 transitions between ZW and XY, half of those transitions being found in geckos.

It is also possible to map those sex-associated loci to reference genomes to identify syntenic blocks that may be repeatedly recruited during sex-chromosome evolution. For example, in the crested gecko (Correlophus ciliatus), most sex-associated loci map on chicken’s chromosome 10. Some genes may have a higher likelihood to be recruited when a new sex chromosome appears, but whether this can be extended to specific syntenic blocks remains an open question. This is made even more difficult by the fact that sex-determining genes in squamates are not yet known with certainty. This ongoing work on macro-evolutionary dynamics of sex chromosomes will provide interesting findings that may be linked to the evolution of mating strategies and speciation in anoles.

Evolution 2018: Whole Genome Sequencing Sheds Light on Genetic Diversity of Green Anole

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On September 3, 2018

In New Research

Anolis carolinensis (photo by Cowenby, Wikipedia)

Whole genome sequencing approaches are rapidly becoming more accessible and gaining popularity. The development of powerful analytical tools for these data has enabled novel approaches to answering outstanding evolutionary questions. Yann Bourgeois, a post-doc at NYU- Abu Dhabi, is the first to take a whole genome approach to understand the population genomics of Anolis carolinensis in the southeastern United States. Yann presented his work in a poster at Evolution 2018 in Montpellier.

Yann sequenced 27 individuals from across the native range representing the five unique genetic clusters (Gulf Atlantic, Carolinas, North Eastern Florida, North Western Florida, South Florida). He found that the Gulf Atlantic and Carolina populations were nested within the Florida populations, supporting the hypothesis of a northward expansion from southern Florida. He was able to estimate that this colonization of regions north of Florida likely occurred in the past 100,000 years. Interestingly, he also found that this dispersal event was associated with a reduction in X chromosome diversity, suggesting that dispersal was either male biased or that there has been positive selection on the X chromosome.

Whole genome sequencing of 27 individuals from across the native range reveals population genetic structure

Taking this one step further, Yann then investigated patterns of recombination via secondary contact among the genetic clusters. Yann and his colleagues found that there has been gene flow between clusters over periods of secondary contact with interspersed periods of isolation. Limited introgression between Florida and the northern populations suggests local adaptation in the northern populations.

Yann and his colleagues have provided an interesting first look at the evolutionary history of Anolis carolinensis from a genomic perspective. The revealed patterns of expansion, reduced diversity, isolation, and secondary contact raise interesting questions about the origin of new genetic clusters (and perhaps species) and their maintenance with ongoing or periodic gene flow.

For more information on this exciting research, check out the pre-print of the manuscript.

Evolution 2018: Dominica Anoles Change Up Their Displays when Faced with New Competition

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On August 25, 2018

In Education and Anoles, Introduced Anoles, New Research, Research Methods

Claire Dufour, Postdoctoral Fellow at Harvard University, presents her research at the 2018 Joint Congress on Evolutionary Biology in Montpellier, France.

In another excellent study exploring the effects of anthropogenic activity on evolution in anoles, Postdoctoral Fellow Claire Dufour is investigating how the recent introduction of Anolis cristatellus from Puerto Rico to the island of Dominica may be driving changes in the display behavior of Anolis oculatus, a Dominica native. Specifically, Dufour is asking whether interactions between the A. cristatellus and A. oculatus are consistent with patterns of Agonistic Character Displacement, in which interference competition between the newly sympatric species results in shifts in traits affecting the rate, intensity, and outcome of interspecific aggression.

To begin, Dufour and colleagues constructed a pair of robots that mimicked the typical look and display behavior of a male A. oculatus and A. cristatellus. She then traveled across Dominica and presented over 130 wild male A. oculatus with one of the two robots, and recorded the display behavior exhibited in response. Beyond measuring the duration of the response display, Dufour also tracked the proportion of time spent by the A. oculatus engaging in any of nine specific display behaviors, such as dewlap extensions, push ups, nuchal crest presentations, and others. By repeating this experiment among populations of A. oculatus existing sympatrically with A. cristatellus, as well as populations not yet invaded by A. cristatellus, Dufour was then able to ask whether variation in display time or composition among the native anoles could be attributed to the presence of A. cristatellus. Indeed, this turned out to be the case.

Anolis oculatus living in allopatry from the introduced A. cristatellus were found to engage in longer display bouts when presented with the conspecific robot, and shorter display bouts when presented with the unfamiliar A. cristatellus robot. Alternatively, A. oculatus occupying habitats already intruded by the A. cristatellus increased the duration of time spent displaying, regardless of which robot was presented. In addition, A. oculatus were also found to alter the behavioral composition of their displays when occupying habitats shared by the introduced A. cristatellus.

Dufour and colleagues capitalized on a rare opportunity to document the very early stages of a species invasion, and in turn improve our understanding of how human-mediated species introductions can promote evolutionary change. As changes in behavior are often the first response to novel competition, these results are consistent with the criteria of Agonistic Character Displacement, and support the claim that the introduction of crested anoles in Dominica has indeed driven a shift in the behavior of native anole communities. While the consequences of these shifts on the outcome of interspecific competition are still unclear, it will be interesting to see how differences in display behavior develop over time, and further, whether these initial changes in display behavior could lead to additional shifts in behavior or morphology among these newly interacting species.

Evolution 2018: Speed Is Key for Anoles in the City

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On August 25, 2018

In Education and Anoles, New Research, Research Methods

Dr. Kristin Winchell at the 2018 Joint Congress on Evolutionary Biology

Human activity is well recognized as having evolutionary consequences, and studies on the prolific Anolis genus continue to show us just how adaptable these lizards can be. Dr. Kristin Winchell, a Postdoctoral Research Associate at Washington University in St. Louis, MO, is investigating the relationship between human activity and evolution in Puerto Rican crested anoles, with a current focus on how selection across urban habitats might be driving changes in morphology and behavior among the lizards.

In an elegantly designed study, Winchell and colleagues collected over 120 male crested anoles (Anolis cristatellus) from forests and urban areas across the island. The team then assessed the ability of these anoles to perform a series of tasks representing normal daily activities, such as sprinting and clinging. By comparing anole performance on natural substrates like wood to their performance on more urban substrates such as concrete and metal, the team determined that the lizards consistently performed better on natural substrates, yet decreased their velocity when perches were inclined. Specifically, the crested anoles sprinted at less then half of their maximum speed on painted concrete, up to 32% slower on metal compared to wood bark tracks, and as much as 34% slower when surfaces were steeply inclined.

Winchell and colleagues measured differences in limb length and toe pad morphology among urban-caught and forest-caught anoles.

In addition to performance assessments, detailed scans of toe pad and skeletal morphology were collected and analyzed, allowing Winchell to identify differences in morphological traits underlying any variation in performance. Upon comparison, the pattern was clear: lizards living in cities had significantly longer limbs, more lamellae on their front toe pads, and larger overall rear toe pads. Longer hindlimbs in particular were found to positively influence velocity across substrate types, surely a selective advantage for anoles tasked with sprinting between the amply spaced urban perches. However, the urban phenotype is not without cost, as longer forelimbs were found to negatively influence velocity on more steeply inclined surfaces, as well as increasing the lizard’s likelihood of slipping. As all urban populations measured shared these phenotypic traits, however, the advantage of increased speed seems to be worth the costs.

As rates of urbanization continue to increase, further studies examining the response of taxa adapting to urban environments will be imperative. With Winchell’s plan to explore performance and morphological differences in other anole species living across the urban-forest continuum, it will be exciting to learn how these traits are affected within species originating from other territorial and arboreal microhabitats.

A Case of Cryptic Back-Introduction

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On August 21, 2018

In New Research

Figure 1. Native and non-native ranges of Anolis sagrei. Map from Kolbe et al. (2017).In this study, Kolbe and collaborators (2017) surveyed A. sagrei populations across Cayman Brac. First, they looked for red-dewlapped lizards to determine whether invasive A. sagrei from Grand Cayman have invaded Cayman Brac. Second, they collected brown anole lizards on Grand Cayman and Little Cayman to determine the source of red-dewlapped A. sagrei. For all lizards captured, they quantified dewlap phenotypes (i.e., reflectance spectra) using spectrophotometric methods, measured structural habitat use (i.e., perch height and diameter) and body size (i.e., snout-vent length (SVL) and mass), and genotyped ten nuclear microsatellite loci. For lizards with intermediate multilocus genotypes or with a genotype that did not match their island, they sequenced mitochondrial DNA (mtDNA) haplotypes (ND2) to test for nuclear-mitochondrial mismatches. Genomic data was combined with previously published microsatellite genotypes (Kolbe et al. 2008) and mtDNA (ND2) sequences for the Cayman Islands (Kolbe et al. 2004, 2007). With these data, they evaluated whether invasive A. sagrei from Grand Cayman have been introduced to native populations on Cayman Brac, and if so, whether invasive lizards have interbred with native lizards.

Under current trends of globalization, human activities impact the distribution of species by facilitating dispersal of propagules. Human-mediated dispersal prevents geographic distance from being a barrier to the introduction and movement of many species. These long-distance colonization events can gather evolutionary distinct lineages that might have been separated for millions of years (e.g., Kolbe et al. 2004). Moreover, dispersal events can potentially reintroduce individuals from an invasive population back into their native range; either back into their original source population or to any part of their native range. This previously undocumented dimension of biological invasion was termed cryptic back-introduction by Guo (2005).

Anolis sagrei is an excellent colonist, judging by its geographical distribution. This species has reached many islands and mainland areas in the Caribbean by overwater dispersal (Williams 1969). About 2.5 million years ago, A. sagrei naturally colonized Cayman Brac and Little Cayman. These populations subsequently differentiated into the yellow-dewlapped endemic subspecies A. sagrei luteosignifer on Cayman Brac and the red-dewlapped A. s. sagrei on Little Cayman (Schwartz and Henderson 1991); the dewlap (i.e., an extendible flap of skin attached to the throat) is used for mate attraction, male-male and interspecific competition, and predator deterrence (Losos 2009). However, this species failed to naturally colonize the third of the Cayman Islands, Grand Cayman. In the early 1980s, through human-mediated dispersal, a red-dewlapped form of A. sagrei established on Grand Cayman. These populations resulted from the introduction of genetically admixed lizards from non-native populations in south Florida (Minton and Minton 1984; Kolbe et al. 2004, 2008; Figure 1). Since then, inter-island supply shipments by air and sea within the Caymans could have transported invasive and native brown anole lizards among the three islands. Kolbe et al. (2017) explored whether cryptic back-introduction is occurring in brown anole (A. sagrei) lizards and the implications of this type of invasion for native populations.

Figure 2. Results of PCA for dewlap reflectance (Kolbe et al. 2017).

Kolbe et al. (2017) found no differences among islands in structural habitat use. They conducted a principal component analysis (PCA) for dewlap reflectance data using the average wavelength of each lizard. PCA results show that there is strong differentiation in dewlap reflectance between yellow-dewlapped lizards on Cayman Brac and the red-dewlapped lizards on Little Cayman and Grand Cayman (Figure 2), which supports their field observations of red-dewlapped lizards occurring on Cayman Brac (Figure 3B). This suggests the introduction of brown anole lizards to Cayman Brac from either of the two other Cayman Islands.

Figure 3. Examples of Anolis sagrei dewlaps from the Cayman Islands (Kolbe et al. 2017).

Furthermore, this study reports strong population-genetic structure among the three Cayman Islands and evidence for non-equilibrium. They identified intermediate multilocus genotypes between Grand Cayman and Cayman Brac (Figure 4). Also, the authors found an intermediate microsatellite genotype in one individual from Cayman Brac. This lizard had a red dewlap and a mtDNA haplotype from Grand Cayman. This mismatch among genetic and phenotypic data suggests that A. sagrei lizards (with different colored dewlaps) from Grand Cayman and Cayman Brac are interbreeding.

Figure 4. Results of a PCoA using multilocus genotypes from ten microsatellite loci (Kolbe et al. 2017).

This study reports the first evidence of cryptic back-introduction; however the frequency with which this phenomenon occurs is still unknown. By studying cryptic back-introductions we can eventually understand how lineages change though a brief period of isolation from its native range and determine if these are incompatible when brought together again. Likewise, future studies should address how phenotypic variation affects ecological interactions with native species and its consequences.

Article:

Kolbe, J. J., J. E. Wegener, Y. E. Stuart, U. Milstead, K. E. Boronow, A. S. Harrison, and J. B. Losos. 2017. An Incipient Invasion of Brown Anole Lizards (Anolis sagrei) Into Their Own Native Range in the Cayman Islands: A Case of Cryptic Back-introduction. Biological Invasions 19:1989–1998.

Cited Literature:

Guo, Q. 2005. Possible cryptic invasion through “back introduction”?

Kolbe, J. J., R. E. Glor, L. R. Schettino, A. C. Lara, A. Larson, and J. B. Losos. 2004. Genetic variation increases during biological invasion by a Cuban lizard. Nature 431:177–181.

Kolbe, J. J., A. Larson, and J. B. Losos. 2007. Differential admixture shapes morphological variation among invasive populations of the lizard Anolis sagrei. Molecular Ecology 16:1579–1591.

Kolbe, J. J., A. Larson, J. B. Losos, and K. de Queiroz. 2008. Admixture determines genetic diversity and population differentiation in the biological invasion of a lizard species. Biology letters 4:434–437.

Losos, J. B. 2009. Lizards in an Evolutionary Tree: Ecology and Adaptive Radiation of anoles. University of California Press.

Minton SA, Minton MR (1984) Anolis sagrei (brown anole). Herpetol Rev 15:77

Schwartz A, Henderson RW (1991) Amphibians and reptiles of the West Indies: descriptions, distributions, and natural history. University of Florida Press, Gainesville

Williams, E. E. 1969. The ecology of colonization as seen in the zoogeography of anoline lizards on small islands.

ESA 2018: The Consequences of Malarial Infection on the Puerto Rican Yellow-Chinned Anole in Post-Hurricane Conditions

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On August 19, 2018

In New Research, Research Methods

Reduced host fitness and impaired immune functions are some of the most well-known consequences of parasitic infections. However, some parasites play important ecological roles by influencing their host’s populations and community composition. In eastern Caribbean islands, the malaria parasite Plasmodium azurophilum has been suggested to mediate competition and determine distribution patterns on some anole species. In Puerto Rico, P. azurophilum is known to infect at least five Anolis species – its main host being the yellow-chinned anole (Anolis gundlachi).

David Clark, a master’s student at the University of Puerto Rico – Río Piedras Campus, along with his research mentor (Dr. Miguel A. Acevedo), assessed the negative ecological consequences of P. azurophilum infection on A. gundlachi within the Luquillo Experimental Forest in eastern Puerto Rico. They quantified this by measuring body condition, dewlap size and site fidelity, all of which were exclusively measured in male anoles, as these are the most often infected by P. azurophilum. Moreover, to determine if infected individuals perform worse after a major disturbance event, the body condition was measured again after Hurricane Maria. They used the residual index for body condition, which is calculated using the regression of the log weight and log size. Dewlap size was measured by taking photos of anoles with their dewlaps extended and calculating the area in ImageJ. To diagnose the presence of P. azurophilum infection, blood samples were collected and then examined using a light microscope under oil immersion. Finally, to examine movement patterns and quantify the site fidelity of male individuals, they conducted a mark-resight study within the forest. For statistical analysis they performed linear regression for body condition and dewlap area, and log-linear regression for distance moved.

Tagged male Anolis gundlachi (a) and Plasmodium under oil immersion (b, c & d) (Image by David Clark)

David and Miguel found that P. azurophilum infection did not influence the site fidelity of A. gundlachi males, and that infected individuals tend to exhibit slightly larger dewlaps. The presence of this malaria parasite did not seem to negatively influence body condition before Hurricane Maria. However, their results show that after this major disturbance, body condition was better for infected anoles, suggesting that these individuals are more tolerant to disturbance conditions than the uninfected ones. All in all, no evidence was found to suggest that P. azurophilum infection has negative consequences on the ecological factors assessed here on A. gundlachi. David and his team are currently performing experimental competition trials to assess intraspecific interactions between infected and uninfected yellow-chinned anoles, as well as immunological studies to determine immune responses to infection. Future studies could possibly bring light on the ecological consequences of interspecific interactions between Puerto Rican anoles infected with malaria parasites.

The Luquillo Experimental Forest after Hurricane Maria (Image by Miguel A. Acevedo)

 

 

 

 

 

Interspecific Differences in Genetic Divergence among Populations of Anolis Lizards in Cuba

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On August 17, 2018

In New Research

Anolis allisoni. Photo by Masakado Kawata

Cuba is a fascinating country and the largest island in the Caribbean. Cuba has the highest diversity of Anolis lizards, including more than 60 species (see my Instagram page for photos of Cuban anoles and landscapes).  Antonio Cádiz, Luis M. Díaz (National Museum of Natural History of Cuba) and a member of my lab published a paper comparing genetic divergence of Anolis species within Cuba (Cádiz et al. 2018, Zoological Letters, 4:21). The study was conducted when Tony was a PhD student at Tohoku University and lecturer at Havana University.

We constructed a phylogeny using nuclear and mitochondrial genes of 303 individuals from 33 Cuban Anolis species (Fig.2) . The phylogeny presented in this study follows the most comprehensive sampling of Cuban Anolis species to date. We added five species which had not been sequenced previously. We also estimated another phylogeny using mitochondrial genes of 51 Cuban and 47 non-Cuban Anolis species for estimated relative species ages (Fig.S3).

 

Map of Cuba showing our sampling locations.

Then, we tried to estimate factors affecting interspecific (or interclade) differences in genetic divergence among populations of Cuban Anolis species. We considered species age, environmental heterogeneity within species ranges, and ecomorph type as putative factors. For this purpose, we examined genetic divergence within species by using 177 populations of 26 species.The sampling locations of these species were selected for the best feasible coverage of known geographic ranges of each species. Phylogenetic Generalized Least Squares (PGLS) analyses showed that species age was positively correlated with species’ average genetic divergence among populations.

Previous studies have indicated deep interpopulation genetic divergence found in several Anolis species. Our results showed that relavie differences in genetic divergence was largely affected by species age and geographic distances within species (Fig. 3). This indicates that older species could have more divergent populations within species.

Phylogeny of Cuban anoles.

Cádiz, A., N. Nagata, L. Díaz, Y. Suzuki-Ohno, L.Echenique-Díaz, H. Akashi, T. Makino and M. Kawata. (2018) Factors affecting interspecific differences in genetic divergence among populations of  Anolis lizards in Cuba. Zoological Letters 4:21 [Open Access] https://doi.org/10.1186/s40851-018-0107-x

Perch Use by Anolis polylepis Peters, 1874 (Polychrotidae) in a Tropical Humid Forest at the Piro Biological Station, Costa Rica

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On August 14, 2018

In Natural History Observations, New Research, Notes from the Field, Research Methods

Morazán Fernández, F., Gutiérrez Sanabria D. R., Coello-Toro H. L., Arévalo-Huezo, E. Ioli, A. G., Díaz Gutiérrez, N., Guerra, L. F, Burbano, D., Guevara, C., Lobos, L., Rico-Urones, A., Cortés-Suárez, J. E, Jiménez, R., Reinke, H., Narváez, V., Aranda, J.M. 2013. Relación entre la fauna silvestre y las plantaciones de palma africana (elaeis guineensis) y su efecto en la producción de pequeños y medianos productores en la península de osa, Costa Rica. Instituto Internacional de Conservación y Manejo de Vida Silvestre, Universidad Nacional, Costa Rica. Pp 104.

This image was taken as part of the integrated course developed by the XXIII promotion of the Masters in Conservation and Wildlife Management of the National University of Costa Rica.

Individuals of a species use habitats on different ways for refuge, feeding, reproduction, or perching. We studied the variation on perch use between sex and age classes of Anolis polylepis at the Piro Biological Station, Costa Rica. Our results point to a similar perch use pattern between sex, but different between age classes, considering only the lowest and
highest perches. Adult females and males use herbaceous and shrubby vegetation and avoid leaf litter. Juveniles use herbaceous vegetation and leaf litter, but avoid shrubby vegetation. We suggest that adult males use higher perches to defend territory.
Conversely, juveniles use lower perches to avoid predators and foraging. Adult females use middle and high perches. This result is in contrast with previous studies on this species.

Cortés-Suárez, J. E. and N. Díaz-Gutiérrez. 2013. Perch use by Anolis polylepis Peters, 1874 (Polychrotidae) in a tropical humid forest at the Piro Biological Station, Costa Rica. Herpetology Notes 6: 219–222.

Halt the Bustle of City Life: Thermal Spikes from the Urban Heat Island Slow Development of Anole Embryos

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On July 26, 2018

In Introduced Anoles, New Research

A brown anole emerging from the egg.

There is much talk these days about how human land use (e.g. urbanization) impacts wildlife. Although anoles have often taken center stage in this discussion (Winchell et al. 2016; Tyler et al. 2016;  Chejanovski et al. 2017; Lapiedra et al. 2017; Winchell et al. 2018), most of this work has focused on measuring phenotypes of adult males. Very little work has been done to understand how massive habitat alteration impacts early life stages even though we know that these stages are extremely sensitive to environmental disturbance and have the potential to impact population dynamics (Carlo et al 2018). Embryos are particularly sensitive to changes in the environment because they lack the ability to respond to unfavorable conditions by adjusting their behavior (i.e., they can’t run away). Since the 1980’s, we’ve known that egg mortality can have massive effects on population densities and even determine how these densities cycle from year to year (Andrews 1982; Andrews 1988; Chalcraft and Andrews 1999). Still, comparatively little attention is given to embryo development and egg survival when considering how habitat alteration impacts species.

In a newly published paper (Hall & Warner 2018), we sought to understand how extreme ground temperatures in cities and suburbs (i.e., the urban heat island effect) influence patterns of embryo development. Due to a lack of canopy cover (i.e., trees) and an abundance of heat-absorbing surfaces (e.g., concrete), cities and suburbs tend to be much warmer than adjacent forested areas, and this means nest temperatures are higher in urban and suburban areas compared to adjacent forested sites (Tiatragul et al. 2017).  Warm temperatures often have positive effects on embryo development; however, extremely warm temperatures can cause mortality and even slow developmental rates (Sanger et al. 2018).

Figure 1. An overview of our experimental design to understand how urban incubation regimes impact embryo development and survival. Eggs from both forest and city populations were factorially distributed into forest and city incubation treatments. At approximately a quarter of the way through development, some eggs were exposed to a spike in temperature measured from the field (either 39 or 43 °C peak). Eggs completed development at their assigned incubation profile (city vs. forest) and hatchling growth and survival were monitored in the lab for three months.

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JMIH 2018: The Curious Case of Bark Anoles

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On July 20, 2018

In New Research

The Bark Anole (Anolis distichus ignigularis) from the Río Recodo. Photo from Richard Glor’s Flickr.

The Bark Anole (Anolis distichus) is a highly polymorphic lizard widely distributed in Hispaniola. Anolis distichus is divided into 16 subspecies with dewlap colors ranging from deep wine red to pale yellow (Glor and Laport 2012). In the early days scientists, such as Albert Schwartz, argued that A. distichus is divisible into multiple subspecies according to an analysis of variation in body color and dewlap pigmentation. But, are they really subspecies?

During the 2018 Joint Meeting of Ichthyologists and Herpetologists (JMIH), Richard Glor shared his lab’s advances on the curious case of Bark Anoles. Anolis distichus populations have ecological, phenotypic and genetic differences. Previous studies show a correlation between dewlap phenotype and environmental variation; in drier habitats, lizards have smaller, brighter, yellow dewlaps, while those in wetter habitats have larger, less bright, orange dewlaps (Ng et al. 2012).

Previously, the Glor Lab found strong support for the hypothesis that A. distichus is comprised of numerous genomically distinct populations (MacGuigan et al. 2016). Genetic divergence was associated with a biogeographic barrier, but not with dewlap color. Also, they found evidence for hybridization in contact zones with limited gene flow and intrinsic reproductive isolation between subspecies (MacGuigan et al. 2016; Ng et al. 2016). Overall, these studies suggest that geographic isolation, as well as ecological specialization, contribute to speciation.

The Glor Lab continues putting together the pieces of the puzzle. Most recently, they sequenced and assembled whole genome sequence data for A. distichus to identify the genomic basis for species differences and speciation.

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