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Early Life Histories, Ocean Currents, and the Population Genetics of Caribbean Reef Fishes

Myra J. Shulman and Eldredge Bermingham
Evolution
Vol. 49, No. 5 (Oct., 1995), pp. 897-910
DOI: 10.2307/2410412
Stable URL: http://www.jstor.org/stable/2410412
Page Count: 14
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Early Life Histories, Ocean Currents, and the Population Genetics of Caribbean Reef Fishes
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Abstract

Tropical reef fishes, along with many benthic invertebrates, have a life cycle that includes a sedentary, bottom-dwelling reproductive phase and a planktonic stage that occurs early in development. The adult benthic populations occupy disjunct, patchy habitats; the extent of gene flow due to dispersal of the planktonic life stage is generally unknown. We investigated dispersal, gene flow, and endemism in eight species of Caribbean reef fishes that varied in two life-history traits that may affect dispersal ability: egg type (pelagic and nonpelagic) and length of planktonic (usually larval) life. Using restriction endonuclease analyses of mitochondrial DNA (mtDNA), we estimated the degree of genetic differentiation among six populations of each of the eight species; these populations came from widely separated locales, occupying both the northern and southern current tracks within the Caribbean. In addition, we calculated mtDNA divergence between two of the study species and their sister taxa in the eastern Pacific. The transisthmian taxa have been isolated from one another for approximately 3 million yr and thus provide a divergence measure against which to assess intra-Caribbean mtDNA distances. Mean sequence divergence observed among conspecific Caribbean mtDNA haplotypes in each of the eight fish species was small, less than 0.7% for all but one species. This level of divergence is roughly one order of magnitude less than mtDNA divergence between Caribbean/eastern Pacific sister taxa. For each of the eight species of fishes, the predominant mtDNA haplotype was widespread in the Caribbean. Populations located in different major surface currents were no more differentiated from one another than populations occupying the same current track. These results suggest that there is considerable gene flow throughout the Caribbean, and that this gene flow has not been constrained by present-day ocean currents. We found statistically significant population subdivision for three Caribbean fish species, though between-population variance accounted for only 8%-17% of the total. Fishes showing population structure were: Stegastes leucostictus (nonpelagic eggs; short planktonic life); Gnatholepis thompsoni (nonpelagic eggs; long planktonic life); and Halichoeres bivittatus (pelagic eggs; short planktonic life). These results suggest that neither egg type nor length of larval life is a simple predictor of geographic structure in reef fish populations.

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