Evolution 2014: Ecomorphological Analysis of Scale Number in Anoles

Hanna Wegener talks about Anolis scales at Evolution 2014.

Talks are underway at Evolution 2014 and anoles are already off to a strong start! Early this morning, Hanna Wegener, a Ph.D. student at the University of Rhode Island, discussed some of her work on the diversity in scale size in Anolis lizards. The work she presented was conducted in collaboration with Gabe Gartner and Jonathan Losos from Harvard University. Hanna started by discussing the adaptive radiation of anoles in the Caribbean. As a community, she said, we know quite a bit about how certain morphological traits, namely skeletal dimensions and lamella counts (i.e., number of toe pad scales) differ among ecomorphs and among different climatic habitats. Scale number, however, remains comparatively unexplored in anoles. For her study, Hanna examined ventral and dorsal scale counts in anoles. Her sampling strategy was impressive – by mining the collections in the Museum of Comparative Zoology at Harvard University, she was able to get scale counts for well over 100 anole species, and Caribbean anoles were particularly well represented in her dataset.

She first sought to examine the relationship between scale number and climate. There are prevailing ideas regarding how scale size and number should relate to climate. Specifically, Michael Soulé and Charles Kerfoot have posited that larger scales are advantageous in hot environments because their greater surface area increases radiative efficiency. Larger scales are also thought to reduce water loss in dry environments. Thus, lizards in hot, dry environments should have fewer, larger scales than lizards in cool, wet environments. Hanna found a positive relationship between scale number (both dorsal and ventral) and precipitation, but she did not find a significant relationship between scale number and temperature.

Hanna showing the variation in scale number and size among anoles. The top two rows show dorsal scales, whereas the bottom two rows show ventral scales.

Hanna then asked whether scale number relates to structural microhabitat use. Here the study became much more exploratory and exciting because, if there is little known about the relationship between climate and scale number, there is even less known about the relationship between scale number and microhabitat use. Hanna found significant differences among ecomorphs in scale number. She found that higher perching ecomorphs, such as crown-giants and trunk anoles, tended to have more, smaller scales. Lizards that perched lower and used broad surfaces, such as trunk-ground species, tended to have fewer, larger scales. Although the precise mechanism underlying this relationship remains unknown, Hanna posited that aspects of microclimate, such as temperature, might vary with structural habitat, which may in turn drive scale number patterns. She also suggested that the observed patterns of scale number variation might represent correlated evolution, such that scale number covaries with a trait that relates to differences in structural microhabitat use. Hopefully Hanna’s study leads to more research on the significance of scale number in anoles and other lizards.

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Martha Muñoz

Martha is a postdoctoral researcher in Sheila Patek's laboratory at Duke University. She received her Ph.D. at Harvard University, where she studyied the evolutionary ecology and thermal physiology of anoles, focusing on the cybotoid anoles from the Dominican Republic. Martha serves as Conference Editor for the Anole Annals.
Website: www.marthamunoz.weebly.com