Author: Kristin Winchell Page 5 of 8

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.

Bright and early on the last day of the annual Evolution meeting, James Stroud (Florida International University) presented his work on character displacement in novel communities of introduced anoles in Miami. In this elegant use of a natural experiment, James looked at the novel co-existence of two anoles in their introduced range and wondered if character displacement was occurring as predicted when two ecologically similar species are found in sympatry. Specifically, James wanted to know if Anolis cristatellus and Anolis sagrei would shift their habitat use when in sympatry, resulting in correlated shifts in morphology. These species are both trunk-ground anoles of roughly the same body size. They are native to Cuba/Bahamas and Puerto Rico (respectively) and are diverged by ~50 million years.

James hypothesized that in their introduced range in Florida, these two species would diverge ecologically in sympatry but be more similar in allopatry. He found that in allopatry, both species attained similar relative abundances and perched at similar heights. However, in sympatry, both decline in relative abundance suggesting that these species are interacting strongly with one another. Even more interesting, in sympatry A. sagrei perches lower and spends more time on the ground than it does in allopatry, while A. cristatellus perches higher!

Next James hypothesized that these ecological shifts could lead to shifts in morphology. If A. sagrei is spending more time on the ground, perhaps longer limbs would be favored. Similarly, if A. cristatellus is spending more time higher up in the trees, perhaps there would be selection for stickier toepads. As predicted, A. sagrei had longer forelimbs and hindlimbs in sympatry. However, he did not find any difference in toepad morphology between sympatric and allopatric populations of A. cristatellus. Instead, he observed that A. cristatellus in sympatry with A. sagrei had significantly smaller heads.

James ended by wondering if alternative behavioral and social mechanisms may drive these observed shifts in head morphology. Either way, this case study provides an interesting insight into how a complex range of adaptive responses can result from a seemingly simple ecological interaction.

At last night’s poster session, undergraduate Derek Briggs (U. Mass. Boston) presented findings from his senior capstone project in which he looked at several traits related to dominance and health. Using a dataset of x-rays and dewlap photos collected over a 4 year period from various urban and forest sites across Puerto Rico (by Kristin Winchell), Derek looked at body size, body condition, dewlap size, and injury rates (broken bones and missing digits) to see if there was a difference in frequency between urban and forest habitats.

Derek and his co-authors chose these traits because they thought they might be impacted by shifts in lizard density and distribution in the urban habitat which may lead to increased male-male competition. Specifically, in urban habitats, lizards tend to perch closer to one another because the potential perches are more clustered. This increase in local density could lead to increased encounter rates and fights over optimal perch sites, food resources, or mates. Derek hypothesized that this shift in distribution should lead to shifts in these traits, although he did not have a prediction about the direction of these shifts.

Derek Briggs with his poster.

Derek found that urban lizards were consistently larger than forest lizards in terms of snout-vent-length (SVL) but that body condition (mass~SVL) did not consistently differ between sites. Although all paired populations had significant differences in body condition, in some municipalities lizards were fatter in urban habitats and in some they were fatter in forests. In terms of dewlap size, Derek did not find any significant trends, although he still has quite a few dewlap photos to analyze still, so stay tuned!

In terms of injuries, Derek did not find significant differences between forest and urban animals for bone breaks or missing digits. However, these are rare events to begin with, so it is possible that a much larger sample size is needed to detect a difference. His findings do suggest a trend of more bone breaks in urban populations, and more missing digits in forest populations. He attributes this trend to either elevated male-male competition in urban habitats or differences in predator communities.

We look forward to seeing the full results from Derek’s honors thesis.