Population genetics of the fissiparous holothurian Stichopus chloronotus (Aspidochirotida) on the Great Barrier Reef, Australia |
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Authors: | S Uthicke J A H Benzie E Ballment |
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Institution: | (1) Australian Institute of Marine Science PMB No 3, Townsville, Queensland 4810, Australia e-mail: S.Uthicke@aims.gov.au, AU |
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Abstract: | Population genetic structure was studied in one nearshore and two offshore populations of Stichopus chloronotus, a common holothurian species on Indo-Pacific coral reefs. Genetic variation at five polymorphic loci was examined using
allozyme electrophoresis. The nearshore population consisted almost exclusively of male individuals, and more males than females
were found in all populations studied. Deviations of heterozygosity from that predicted under Hardy-Weinberg equilibrium indicated
that asexual reproduction occurred in all populations. Estimates of the level of asexual reproduction using the ratios of
the number of sexually produced individuals to sample size, observed genotypic diversity to expected genotypic diversity,
and number of genotypes to sample size confirmed that this reproductive mode was more important at the nearshore reef compared
to the two offshore reefs. There were large differences in genotypic frequencies between males and females. F-statistics on
clonal genotypic frequencies were not statistically significant between populations for neither females or males, suggesting
high dispersal of larvae between reefs. A higher mortality of females during larval or early post-settlement stages, or reduced
dispersal capability of female larvae are the most likely reasons for biased sex ratios.
Accepted: 23 November 1998 |
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Keywords: | Holothurian Population genetics Asexual reproduction Sex ratio Electrophoresis |
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