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Stepping-stone gene flow in the solitary coral Balanophyllia elegans : equilibrium and nonequilibrium at different spatial scales

Stepping-stone gene flow in the solitary coral Balanophyllia elegans : equilibrium and... 227 123 123 3 3 M. E. Hellberg Center for Population Biology University of California at Davis 95616 Davis California USA Department of Zoology University of California at Davis 95616 Davis California USA Center for Marine Biotechnology and Biomedicine Scripps Institution of Oceanography University of California at San Diego 92093-0202 La Jolla California USA Abstract Limited dispersal should result in genetic differences between populations proportional to geographic distances of separation. This association between gene flow and distance can be disrupted by (1) continuing genetic exchange among distant populations, (2) historical changes in gene flow, and (3) physical barriers or corridors to dispersal. The movements of larvae are thought to determine dispersal capability in benthic marine invertebrates. The solitary scleractinian Balanophyllia elegans Verrill possesses crawling larvae capable of only limited dispersal. Paradoxically, however, inferred levels of gene flow between pairs of localities spread over much of the 4000 km range of B. elegans exhibited a weaker relationship with geographical separation than that expected for a linear array of populations in which all genetic exchange takes place between adjacent populations. In this paper, I examined the pattern of gene flow (inferred from the frequencies of eight polymorphic allozyme loci) in B. elegans at a smaller (1 to 50 km) spatial scale to determine (1) whether gene flow at this spatial scale conformed to the expectations of the stepping-stone model, and (2) whether continuing long-distance gene flow or historical changes in gene flow were responsible for the weak relationship between gene flow and distance observed previously at the rangewide spatial scale. Between May and August 1992, I collected 75 adults from each of 18 localities along the coast of Sonoma County, California, USA. These populations of B. elegans were significantly subdivided both among localities separated by 1 to 50 km ( F LT =0.053, Se=0.0075) and among patches separated by 4 to 8 m ( F PL =0.026, SE=0.0023). The observed slope and correlation ( r 2 =0.54) between inferred levels of gene flow and the geographic distance at the 1 to 50 km spatial scale conformed to equilibrium expectations (obtained by simulation) for a linear stepping-stone model, although those from the rangewide spatial scale did not. This implies that the mechanisms conferring patterns of inferred genetic differentiation between localities in B. elegans differ fundamentally with spatial scale. At a scale of 1 to 50 km, continuing gene flow and drift have equilibrated and the process of isolation-bydistance may facilitate local adaptive change. At a broader spatial scale, historical changes in gene flow, perhaps affected by late Pleistocene climatic fluctuations, disrupt the equilibration of gene flow and genetic drift, so that genetic differentiation may not increase continuously with separation between populations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Marine Biology Springer Journals

Stepping-stone gene flow in the solitary coral Balanophyllia elegans : equilibrium and nonequilibrium at different spatial scales

Hellberg, M.
Marine Biology , Volume 123 (3) – Sep 1, 1995
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References (38)

Publisher
Springer Journals
Copyright
Copyright © 1995 by Springer-Verlag
Subject
Life Sciences; Biomedicine general; Oceanography; Ecology; Microbiology; Zoology
ISSN
0025-3162
eISSN
1432-1793
DOI
10.1007/BF00349236
Publisher site
See Article on Publisher Site

Abstract

227 123 123 3 3 M. E. Hellberg Center for Population Biology University of California at Davis 95616 Davis California USA Department of Zoology University of California at Davis 95616 Davis California USA Center for Marine Biotechnology and Biomedicine Scripps Institution of Oceanography University of California at San Diego 92093-0202 La Jolla California USA Abstract Limited dispersal should result in genetic differences between populations proportional to geographic distances of separation. This association between gene flow and distance can be disrupted by (1) continuing genetic exchange among distant populations, (2) historical changes in gene flow, and (3) physical barriers or corridors to dispersal. The movements of larvae are thought to determine dispersal capability in benthic marine invertebrates. The solitary scleractinian Balanophyllia elegans Verrill possesses crawling larvae capable of only limited dispersal. Paradoxically, however, inferred levels of gene flow between pairs of localities spread over much of the 4000 km range of B. elegans exhibited a weaker relationship with geographical separation than that expected for a linear array of populations in which all genetic exchange takes place between adjacent populations. In this paper, I examined the pattern of gene flow (inferred from the frequencies of eight polymorphic allozyme loci) in B. elegans at a smaller (1 to 50 km) spatial scale to determine (1) whether gene flow at this spatial scale conformed to the expectations of the stepping-stone model, and (2) whether continuing long-distance gene flow or historical changes in gene flow were responsible for the weak relationship between gene flow and distance observed previously at the rangewide spatial scale. Between May and August 1992, I collected 75 adults from each of 18 localities along the coast of Sonoma County, California, USA. These populations of B. elegans were significantly subdivided both among localities separated by 1 to 50 km ( F LT =0.053, Se=0.0075) and among patches separated by 4 to 8 m ( F PL =0.026, SE=0.0023). The observed slope and correlation ( r 2 =0.54) between inferred levels of gene flow and the geographic distance at the 1 to 50 km spatial scale conformed to equilibrium expectations (obtained by simulation) for a linear stepping-stone model, although those from the rangewide spatial scale did not. This implies that the mechanisms conferring patterns of inferred genetic differentiation between localities in B. elegans differ fundamentally with spatial scale. At a scale of 1 to 50 km, continuing gene flow and drift have equilibrated and the process of isolation-bydistance may facilitate local adaptive change. At a broader spatial scale, historical changes in gene flow, perhaps affected by late Pleistocene climatic fluctuations, disrupt the equilibration of gene flow and genetic drift, so that genetic differentiation may not increase continuously with separation between populations.

Journal

Marine Biology – Springer Journals

Published: Sep 1, 1995

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