The influence of habitat and climate on the morphology and coloration of peripheral western fence lizard populations in Washington State

Background/Question/Methods

Many widespread species show morphological variation across the unique habitats and climates they inhabit. For reptiles these morphological adaptations such as limb length or body depth are often correlated with habitat use and substrate types. Additionally, body size trends and the degree of pigmentation of reptiles, driven by thermoregulatory requirements, can correspond with the elevation and climate of populations. The blue ventral coloration of Western Fence Lizards (Sceloporus occidentalis) is displayed by both sexes and has social implications as a signaling device but can also be a byproduct of increased melanism in response to thermally challenging environments. We investigated the morphology and coloration of S. occidentalis in Washington State at a coastal beach population, a low elevation forest population, and a high elevation creek canyon population. Our project examined if the contrasting microhabitats of the S. occidentalis populations resulted in adaptive morphologies, and characterized S. occidentalis communities at the species’ northwestern coastal range boundary. To study the relationships between morphology, coloration, and habitat between distinct lizard populations in Washington State, we used handheld and photo analysis methods to obtain head, body, and limb measurements in addition to quantifying belly and throat coloration.

Results/Conclusions

The high elevation creek canyon lizards used rock perches 69% of the time, low elevation forest lizards used trees 67% of the time, and the beach lizards perched on driftwood 97% of the time. Given the distinct substrate use by rock, tree and driftwood inhabiting lizards, our morphological data suggests adaptations between populations. Rock lizards are potentially adapted to navigate their open, rocky habitat with increased running speed from their specialized front fore-limbs, which were the longest of populations. Forest lizards had the shortest front fore-limbs possibly due to reduced running reliance, as they specialized in arboreal perches. Driftwood lizards had the skinniest body condition that could optimize them for cracks in driftwood logs they relied on. The overall body size of the lizards was not clearly correlated with elevation. Beach lizards were the largest, followed by high elevation rock lizards, then low elevation forest lizards, suggesting other factors than climate or elevation select for body size. Beach lizards had bluer and darker bellies than high elevation lizards, and bluer throat patches than the other two sites. Our study suggests morphological and signaling adaptations among populations of S. occidentalis and offers insights into unique communities at the species’ geographic extreme.