All posts by Ken Toyama

The Evolution Of Morphological Diversity In Tropidurine Lizards: the Influence Of Habitat

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Uracentron flaviceps (upper photo) and Microlophus thoracicus (lower photo), two tropidurine lizards adapted to rainforests and deserts, respectively.

I was lucky enough to spend some months working at the Museum of Comparative Zoology of Harvard as part of the Losos lab. There I learned a good deal about anoles and got to meet anole-loving people face to face. Even though this atmosphere tempted me to develop a project related to one of the greatest examples of adaptive radiation, I had other plans in mind involving some of their distant cousins: tropidurine lizards! The results of this study are already published (Toyama, 2017) and I will describe a bit of what I found.

Tropidurinae is a group of lizards whose representatives have diversified across South America. They come in different shapes, colors and sizes, as you would expect from any group of organisms spreading in a diverse territory in terms of habitats, climates and altitudes. Rainforests, deserts, mountains and dry forests are just some examples of the different ecosystems where you can find these lizards. Given this scenario, I wondered if the morphological diversity observed in this clade could be linked to the challenges imposed by the different habitats types found in the continent.

Inspired by similar studies that focused on other lizard radiations, I took measurements of functional morphological traits of several species of lizards coming from 10 out of the 12 genera comprising the Tropidurinae. These traits would allow me to look for a possible correspondence between morphology and habitat.

However, as I was not only interested in the link between morphology and habitat use, but also in the morphological diversity itself, I started looking at purely morphological information. The next figure shows the illustrative results of a Principal Component Analysis (PCA), which tries to separate the species as much as possible based on the morphological measurements. In the figure, we can observe how the dots of each color (representing species of the same genus) occupy a particular zone in the graph. This means that, in general, species of the same genus are, as expected, morphologically more similar between them than to species of other genera (exceptions aside, given the overlaps between some genera).

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Scatter plot showing the morphological space defined by PC1 and PC2. Each dot represents the average values for a species, and species are grouped in genera (colors). Abbreviations are shown for some traits as HL (head length), HW (head width), HH (head height), BW (body width), BH (body height), Dist (distance between limbs), Htoe (longest toe of the hind limb), and Ftoe (longest toe of the forelimb).

Going a bit farther in respect to morphological diversity, Continue reading The Evolution Of Morphological Diversity In Tropidurine Lizards: the Influence Of Habitat