Graduation Year


Document Type




Degree Granting Department

Biology (Integrative Biology)

Major Professor

Henry R. Mushinsky, Ph.D.

Co-Major Professor

Earl D. McCoy, Ph.D.

Committee Member

Gordon A. Fox, Ph.D.

Committee Member

Gary R. Huxel, Ph.D.


Intrinsic survival, Local adaptation, Squamates, Age at maturity, Plasticity


To understand the evolutionary and ecological significance of geographic variation in life

history traits, we must understand whether the patterns are induced through plastic or adaptive

responses. The Eastern Fence Lizard,

Sceloporus undulatus

, exhibits countergradient variation

(larger body sizes, et cetera, in northern, cooler environments; presumed adaptive) in life history

traits across its large geographic range. However, cogradient variation (the expected result from

a plastic response, although not necessarily inconsistent with adaptation) has been suggested as

a null hypothesis, especially on fine geographic scales because of relatively small environmental

changes. Here we focus on life history variation on a fine geographic scale to test whether

cogradient variation is exhibited even though countergradient variation is exhibited at larger

scales, and if so, what mechanisms are involved in the switch. We examined north and south

populations (~2° latitude between) of the

S. undulatus, and the Florida Scrub Lizard, S. woodi

, by

measuring adult body sizes, reproduction, and hatchling body sizes over a two year period and

conducting reciprocal transplants of juvenile lizards each year. Our results indicate cogradient

variation (larger body size in the southern population experiencing a warmer environment) in life

history traits of

S. undulatus

and countergradient variation, a lack of variation in adult body size,


S. woodi along the Florida peninsula. Thus, S. undulatus

exhibits cogradient variation at fine

geographic scales and countergradient variation at larger scales. Reciprocal transplants revealed

that the larger adult body sizes in the southern population of

S. undulatus

could be explained by

longer growth periods allowed by greater intrinsic survival. In

S. woodi,

the larger than expected

adult body sizes in the north could be explained by faster intrinsic and extrinsic juvenile growth

rates in the northern population. Because

S. undulatus and S. woodi

remain distinct species

associated with distinct, though adjacent, habitats, we also looked for habitat-specific

adaptations. The second reciprocal transplant (between species and habitats) revealed habitatspecific

adaptations in juvenile growth rates, but not juvenile survival. Each native species grew

faster and had a higher average probability of reaching size at maturity in their native

environment than did the foreign species.