Complex interactions between topographic heterogeneity and steep
gradients in climate and environmental conditions are commonly assumed to
promote biotic diversification. Using tropical frogs as a model, I investigate the
nature of these interactions that disrupt migration between populations, causing
genetic divergence and speciation. I determine the role of several putative factors
that affect gene flow (Euclidean distances, Least Cost Path (LCP) distances,
topographic complexity, and elevation difference) and promote genetic structure
(FST) between populations of three tropical Andean frog species. Moreover, I
investigate, from an intraspecific perspective, whether montane frog species
display on average larger genetic distances per kilometer relative to lowland
species. Finally, I test if recent genetic divergence caused by topographic
barriers to gene flow is paralleled by independent character systems such as
acoustics and morphological traits in the high Andean frog Dendropsophus
labialis.
Even though the effect of geographic features on migration (and
conversely, FST) was species-specific, LCP and Euclidean distances had the strongest effect on migration rate. Topographic complexity also reduced
migration rate whereas elevation difference did not have an effect. I found that
indeed highland species show larger genetic distances per kilometer between
haplotypes than do lowland species. Also, genetic divergence is strongly
associated with topographic heterogeneity, which is an intrinsic characteristic of
montane regions. Finally, I found that acoustic variation in D. labialis diverges
according to genealogical history, but external morphology does not follow this
relationship. Stochastic processes due to genetic drift appear to be a better
explanatory mechanism for the divergence in calls than adaptive variation. The
strong and congruent divergence observed in acoustic and genetic characters
indicates that these two groups correspond to morphologically cryptic parapatric
species.
Overall, the results of this study suggest some of the mechanisms that
allow tropical mountains to promote intraspecific genetic divergence. The
combined effect of ridges (promoting allopatric differentiation) and environmental
gradients across elevation (promoting parapatric differentiation) are effective
forces that are present mostly in highland biomes. Unfortunately, such biomes
are critically threatened by habitat destruction and climate change, possibly more
than any other biome on earth. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2011-08-3726 |
| Date | 20 October 2011 |
| Creators | Guarnizo, Carlos Enrique |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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