Anole Annals

Color variation of Anolis conspersus on Grand Cayman. Spotted individuals (left) are found in the west of the island and vermiculated ones (right) are found in the east.

Christopher Peterson, a masters student in the Fitzpatrick Lab at the University of Tennessee, studies color variation of Anolis conspersus on Grand Cayman. He found that lizards from eastern Grand Cayman are vermiculated and individuals from the west side are spotted. He hypothesized that color variation along the east-west axis might be due to climatic variation, habitat differences or population structure. He sampled multiple sites across the island and measured air temperature, relative humidity, degree of leaf coverage (shade), perch roughness and perch connectivity. Using a hierarchical Bayesian logistic regression, Christopher did not find correlations between body coloration and climatic variation or habitat differences. He found, however, that spotted individuals have significantly longer tails and vermiculated ones are larger (SVL) on average. Genome wide SNPs will reveal whether population structure can explain variation in coloration between eastern and western populations.

How does the environment an organism experiences during development influence its phenotype, and does the development environment prepare the organism for success in its habitat? Corey Cates, now a Ph.D. student in the Warner Lab at Auburn University, used Anolis lizards to answer this question at the SICB meeting in Portland, Oregon.

Because anoles do not practice parental care, once a female lays an egg, the embryo is at the mercy of the environment. Soil conditions, such as moisture and temperature, will influence how the embryo develops, and can have lasting impacts on that organism’s phenotype. Furthermore, a lizard is expected to have highest fitness when its phenotype matches its environment. Cates designed an experiment that manipulated the development environment, and examined the desiccation performance and survival of hatchlings, following them into adulthood. Anolis sagrei that hatched from eggs left in dry, poor-quality soil experienced lower desiccation rates than those from eggs in moist, high-quality soil. Building upon previously-presented work, Cates showed that adult desiccation tolerance was not heritable. After following adult lizards from each treatment released into both high and low-quality habitats for more than a year, Cates found that desiccation trends persisted, and that organisms from dry incubation conditions performed better in dry habitats than those incubated in more favorable conditions. This study is a fascinating look into how anoles may handle changing climates in the future.

Jake Stercula presents his poster at SICB 2016.

*The following post was written by Chris Robinson, a Master’s student in Matt Gifford’s lab at the University of Central Arkansas.*

Both between and within ecomorphs, anoles can experience a wide range of temperature conditions. As ectotherms, anoles rely on external conditions to thermoregulate, and therefore species found in different environments may have evolved unique biochemical mechanisms to adapt to their respective environments.

Using both field and laboratory studies, Jake Stercula, an undergraduate working with Michele Johnson at Trinity, is investigating how membrane fluidity, which aids in cell function, of the brain is regulated by temperature and lipid composition. The saturated:unsaturated lipid composition ratio controls cell membrane fluidity, where a higher ratio provides less fluidity. Stercula and colleagues hypothesize that species within a thermal environment (warmer or cooler) will have more similar lipid ratios and fluidity than between thermal environments regardless of ecomorph, and that anoles in warmer thermal environments will have a higher saturated:unsaturated lipid ratio.

To test this, they are conducting three studies. First, they quantified body temperature of anoles from warmer and cooler areas within the grass-bush, trunk-crown, and trunk-ground ecomorphs in Puerto Rico (Figure 1). Second, to test for lipid composition plasticity, A. carolinensis male and female pairs were housed in either a 26°C or 35°C room (6 pairs in each). After six weeks, the lizards were sacrificed and their brains were collected to quantify the lipid composition ratio using mass spectroscopy at the University of Texas Health Science Center in San Antonio. Finally, to quantify membrane fluidity, they are growing astrocytes from A. carolinensis at 28°C and 35°C and predict that astrocytes from the warmer condition will be less fluid than those from the cooler condition.

This study could provide novel insight into how anole species have adapted to their thermal conditions. We look forward to seeing the rest of the results!

Figure 1. Body (dark columns) and perch (light columns) temperature comparisons between species that perch in the sun (sun) versus in the shade (shade).

Andrew Battles presents his work on Anolis cristatellus and A. sagrei at SICB 2016.

Greetings from SICB! Sessions are off to a roaring start here in Portland. At Monday’s poster session, Andrew Battles presented his work on the thermal ecology of urban anoles. Andrew, a Ph.D. student working with Jason Kolbe at the University of Rhode Island, presented his work in the poster session for the prestigious Huey award.

Around the world, many natural habitats are being replaced with artificial, heat-absorbing structures, such as concrete and metal. This is a really big deal for the animals that perch on these substrates, particularly ectotherms, which derive their heat from external sources. Andrew examined environmental temperatures and canopy openness at a variety of urban and natural sites in (and around) Miami, Florida. What he found was that urban perches (posts, building walls, etc) were considerably warmer and more exposed than natural perches.

He then examined body temperatures for the lizards Anolis cristatellus and A. sagrei that are commonly found in those habitats. On average, A. sagrei had higher body temperatures than A. cristatellus. Both species benefitted from warmer urban structures early in the morning, as they were able to reach temperatures in their preferred range sooner than in the cooler natural sites. In light of these results, Andrew’s next work will examine patterns of physiological divergence in urban and natural habitats. Congratulations to Andrew for being a finalist (and the sole Anolis ambassador) in this year’s Huey Award Symposium.

Anolis onca basking. Photo by Gabriel Ugueto.

The ecological niche is one of the most controversial concepts in ecology with a long history of debate about its definition and scope. Some authors have suggested that this concept should be abandoned (see for example McInerny & Etienne, 2012a,b,c), while others, including me, consider that this controversial history, and a plethora of definitions, should not preclude its use. However, it needs to be explicitly defined to known exactly we are talking about.

The ecological niche is understood as the set of environmental factors that allow a local population to persist without immigration from others sources (Hutchinson 1959). Some evolutionary ecologists have envisioned the ecological niche as a phenotypic extension of a species and therefore subject to natural selection and other evolutionary process. Based on this, in my doctoral dissertation, I evaluated whether the ecological niche (or more precisely, the climatic niche), as a population-level trait, can promote species diversification in Anolis lizards. Although there are several studies linking organismal and species’ level traits with speciation, there are few exploring this association in Anolis lizards.

Our study exploring this was recently published in the Journal of Biogeography (Velasco et al. 2016). Explicitly, we adopt  Hutchinson’s niche definition using only coarse-grain variables (or the Grinnellian niche dimension; see Soberón 2007). To do this, we compiled an extensive occurrence database for 328 species with help of several colleagues. Using climatic layers from WorldClim database, we calculated a set of niche metrics for species and clades, including mean niche position (based on PCA analyses), niche breadth (based on Mahalanobis distances) and occupied niche space (as a proxy of climatic niche diversity).

We compared how climatic niche breadth and occupied niche space differ among regions (insular vs. mainland) and clades (Fig. 1 & 2). Mainland species and clades tend to exhibit larger niches than Caribbean clades and species (Fig. 1).

These differences were maintained after controlling for range size differences. We suggest that these differences are directly related to the available climatic space in each region. For instance,  Caribbean islands exhibit a limited climatic space in comparison with  mainland regions and therefore insular clades occupy all available climatic conditions in each island (Fig. 2). By contrast, mainland clades are more restricted to climatic conditions and therefore occupy only a portion of all available climatic conditions (Fig. 2).

We correlated these niche metrics with species diversification using a calibrated time tree. We found that anole clades occupying warmer and drier areas diversified more than clades occupying very humid and colder areas. In addition, anole clades with narrow niches tend to speciate more than clades with widespread niches (Fig. 3). Our findings suggest that climatic specialization has played a strong role in anole diversification with differences among insular and mainland settings.

It would be interesting to evaluate whether other traits (e.g., body size, geographical range size, or other Eltonian niche dimensions) also play a similar role on cladogenesis in Anolis lizards and evaluate their relative importance in diversification dynamics.

References

Hutchinson, G.E. (1957) Concluding remarks. Cold Spring Harbor Symposia on Quantitative Biology, 22, 415-427.

McInerny, G.J. & Etienne, R.S. (2012a) Ditch the niche ? is the niche a useful concept in ecology or species distribution modelling? J. Biogeogr., 39, 2096-2102.

McInerny, G.J. & Etienne, R.S. (2012b) Stitch the niche ? a practical philosophy and visual schematic for the niche concept. J. Biogeogr., 39, 2103-2111.

McInerny, G.J. & Etienne, R.S. (2012c) Pitch the niche ? taking responsibility for the concepts we use in ecology and species distribution modelling. J. Biogeogr, 39, 2112-2118.

Soberón, J. (2007) Grinnellian and Eltonian niches and geographic distributions of species. Ecology Letters, 10, 1115-1123.

Velasco, J. A., Martínez-Meyer, E., Flores-Villela, O., García A., Algar, A. C., Köhler, G. and Daza, J. M. (2016), Climatic niche attributes and diversification in Anolis lizards. J. Biogeogr., 43: 134-144. doi:10.1111/jbi.12627

As 2015 comes to an end, now is a good time to reflect on the year in Anole Annals. Fortunately, our good friends at WordPress have provided us with a nice summary.

For all the details on how things went down on Anole Annals in 2015, check out WordPress’s full report.