Title page for ETD etd-11022004-064101


Type of Document Dissertation
Author Taylor, Michael S.
URN etd-11022004-064101
Title Geography, Coloration and Speciation in a Genus of Neotropical Reef Fishes (Gobiidae: Elacatinus)
Degree Doctor of Philosophy (Ph.D.)
Department Biological Sciences
Advisory Committee
Advisor Name Title
Michael E. Hellberg Committee Chair
J. Michael Fitzsimons Committee Member
Mark S. Hafner Committee Member
Mohamed A.F. Noor Committee Member
Jill A. Jenkins Dean's Representative
Keywords
  • Caribbean Sea
  • biogeography
  • speciation
  • phylogeography
  • reef fishes
Date of Defense 2004-10-27
Availability unrestricted
Abstract
Studies of speciation in the marine environment have historically compared broad-scale distributions and presumed larval dispersal to infer the geographic barriers responsible for allopatric speciation. However, many marine clades show high species diversity in geographically restricted areas where barriers are not obvious and larval dispersal should bring sister taxa into contact. Genetic differentiation at spatial scales <1000 km could facilitate speciation by mechanisms other than the gradual accumulation of reproductive isolation during extended allopatry, such as ecological adaptation to local environmental conditions or the rapid evolution of genes tied to mate recognition. The role of each of these possibilities has not been simultaneously explored for any species-rich marine taxon. The most species-rich genus of Neotropical reef fishes is Elacatinus (Gobiidae), with 27 species. I examine potential mechanisms underlying this richness through analyses of three genetic markers to investigate genetic and ecological differentiation between closely related taxa and among island populations.

Phylogenetic analyses indicate that sister taxa of Elacatinus occur within the same oceans but occupy geographically separate ranges. Sister taxa usually differ by coloration, and distantly related sympatric species frequently differ by habitat. These differences suggest that some combination of coloration and ecological differences may facilitate assortative mating in sympatry or at range boundaries. The ranges of several Elacatinus taxa adjoin at Mona Passage and in the central Bahamas, both in the Caribbean Sea. These boundaries separate island populations by as few as 23 km, yet these populations are genetically distinct. Populations not separated by these breaks also show strong genetic structuring. Coalescent analyses suggest these populations have been demographically closed for up to 800,000 years. Such strong genetic structuring suggests that pelagic larvae are retained at natal populations, despite a three week larval duration (determined from otolith growth rings).

My results suggest that local retention of pelagic larvae, coupled with biogeographic breaks, has generated or maintained strong genetic population structure which may facilitate adaptation to local ecological conditions. Such adaptations may explain observed divergence along ecological and coloration gradients. Repeated radiations among allopatrically distributed sister taxa may explain much of the high diversity in Elacatinus.

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