Ecomorphology Of The Mexican Fence Lizards Of The Sceloporus Formosus Group (squamata: Phrynosomatidae)

A central belief of ecomorphological studies is the link between morphology and performance, but, surprisingly few analyses demonstrate this relationship. Fence lizards of the genus Sceloporus offer a useful system for addressing correlations between morphology and performance because they possess keratinized and keeled scales, a distinctive morphological character that might influence water balance. A common observation across different taxa of reptiles is that many organisms in dry habitats have few scales on their bodies, compared to organisms inhabiting moist environments. This pattern is also present in fence lizards. I investigated if the number of dorsal and lateral scales varies across three environmental variables (elevation, temperature and precipitation) for three species of Sceloporus (S. adleri, S. scitulus and S. druckercolini). Among and within species, I found that lizards with the fewest and most heavily keeled scales occur at low elevations and dry environments and lizards with the most and smoothest scales occur at high elevations and moist environments. A compelling hypothesis to explain this pattern is that fewer and larger scales are generally keeled and overlapping reducing skin exposure and hence the amount of evaporative water loss. On the other hand, smaller, more granular scales increase the exposed skin surface area and increase rates of dehydration. To test this hypothesis, the skin resistance to water loss (Rs) was measured on the sides of lizards and the number of lateral scales was counted for this specific area. The relationship between water loss and scalation was as expected, observing the lowest values of Rs with the highest number of lateral scales for all species together and within species. In addition, I tested if water loss was correlated to any of the three climate variables. I found the lowest values of Rs in lizards occurring at highlands, where temperatures tend to be low and water is usually more readily available. As a consequence of the variation in the lizard's morphology (scalation) with their habitat, I proposed a third hypothesis relating the morphology with the performance of the lizards. I predicted that a higher number of scales will be positively correlated with sprint speed. Out of the three species, only S. scitulus increased its performance with a higher scalation. Our results suggest that reptilian changes in scale numbers are correlated with ecological variables such as elevation, temperature and precipitation, and that the number of scales in a population and/or species may be highly plastic in order to maintain a proper osmotic balance. In turn, this important ecomorphological relationship provides also an opportunity to explore trade-offs between the already compromised morphological variation and running performance, as suggested for S. scitulus.