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Genetic evidence for contrasting patterns of dispersal in solitary and colonial ascidians

Genetic evidence for contrasting patterns of dispersal in solitary and colonial ascidians In situ and in vitro observations indicate that brooding colonial ascidians commonly display limited larval dispersal, whilst the larvae of most solitary species are assumed to be widely dispersed. We used allozyme data to determine the population genetic consequences of reproduction and dispersal in a broadcast-spawning solitary ascidian and two brooding colonial species along the central and southern coast of New South Wales, Australia. We surveyed genetic variation at 2 to 9 variable loci for samples collected from 6 to 8 local populations of each of the stalked solitary species Pyura gibbosa gibbosa Heller, 1878; the social Stolonica australis Michaelsen, 1927 and the compound Botrylloides magnicoecum Hartmeyer, 1912. Samples from each local population displayed levels and patterns of genotypic diversity that were consistent with expectations for sexually-derived recruitment of both solitary zooids and separate colonies. However, we found clear differences in the structure of the populations of solitary and colonial species. Genotype frequencies within all nine samples of P. gibbosa gibbosa conformed to expectations for random mating (i.e. Hardy–Weinberg equilibria). Moreover, allele frequencies showed little variation among samples [mean standardised genetic variance (F S T ) =0.002], which implies that local populations are strongly connected by larval dispersal. We estimate (via Wright's “island model”) that gene flow (N e m) within this set of local populations is 125 effective migrants per generation, which is very similar to estimates obtained for other broadcast-spawning taxa in this region. In contrast, genotype frequencies within samples of both colonial species were characterised by large and statistically significant deficits of heterozygotes, consistent with expectations for highly limited dispersal of larvae or sperm. Moreover, local populations were highly differentiated (F S T =0.201 and 0.202 for S. australis and B. magnicoecum, respectively) and N e m was estimated to be ∼1.0 in each case. These values of F S T and subsequent estimates of N e m lie within the range of values reported for other New South Wales taxa with direct larval development, and imply that local populations are effectively closed to immigration. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Marine Biology Springer Journals

Genetic evidence for contrasting patterns of dispersal in solitary and colonial ascidians

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References (28)

Publisher
Springer Journals
Copyright
Copyright © 1997 by Springer-Verlag Berlin Heidelberg
Subject
Environment; Marine & Freshwater Sciences; Freshwater & Marine Ecology; Oceanography; Microbiology; Zoology
ISSN
0025-3162
eISSN
1432-1793
DOI
10.1007/s002270050224
Publisher site
See Article on Publisher Site

Abstract

In situ and in vitro observations indicate that brooding colonial ascidians commonly display limited larval dispersal, whilst the larvae of most solitary species are assumed to be widely dispersed. We used allozyme data to determine the population genetic consequences of reproduction and dispersal in a broadcast-spawning solitary ascidian and two brooding colonial species along the central and southern coast of New South Wales, Australia. We surveyed genetic variation at 2 to 9 variable loci for samples collected from 6 to 8 local populations of each of the stalked solitary species Pyura gibbosa gibbosa Heller, 1878; the social Stolonica australis Michaelsen, 1927 and the compound Botrylloides magnicoecum Hartmeyer, 1912. Samples from each local population displayed levels and patterns of genotypic diversity that were consistent with expectations for sexually-derived recruitment of both solitary zooids and separate colonies. However, we found clear differences in the structure of the populations of solitary and colonial species. Genotype frequencies within all nine samples of P. gibbosa gibbosa conformed to expectations for random mating (i.e. Hardy–Weinberg equilibria). Moreover, allele frequencies showed little variation among samples [mean standardised genetic variance (F S T ) =0.002], which implies that local populations are strongly connected by larval dispersal. We estimate (via Wright's “island model”) that gene flow (N e m) within this set of local populations is 125 effective migrants per generation, which is very similar to estimates obtained for other broadcast-spawning taxa in this region. In contrast, genotype frequencies within samples of both colonial species were characterised by large and statistically significant deficits of heterozygotes, consistent with expectations for highly limited dispersal of larvae or sperm. Moreover, local populations were highly differentiated (F S T =0.201 and 0.202 for S. australis and B. magnicoecum, respectively) and N e m was estimated to be ∼1.0 in each case. These values of F S T and subsequent estimates of N e m lie within the range of values reported for other New South Wales taxa with direct larval development, and imply that local populations are effectively closed to immigration.

Journal

Marine BiologySpringer Journals

Published: Nov 27, 1997

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