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,
in 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.
| Identifer | oai:union.ndltd.org:USF/oai:scholarcommons.usf.edu:etd-4847 |
| Date | 14 July 2010 |
| Creators | Robbins, Travis R. |
| Publisher | Scholar Commons |
| Source Sets | University of South Flordia |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Graduate Theses and Dissertations |
| Rights | default |
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