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SPATIAL SCALE OF GENETIC STRUCTURE AND AN INDIRECT ESTIMATE OF GENE FLOW IN EELGRASS, ZOSTERA MARINA
Author(s) -
Ruckelshaus Mary H.
Publication year - 1998
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1998.tb01635.x
Subject(s) - zostera marina , biology , gene flow , scale (ratio) , genetic structure , ecology , spatial ecology , gene , seagrass , genetic variation , ecosystem , genetics , cartography , geography
In this study, the first investigation of population structure in an aquatic angiosperm, I show that populations of a marine angiosperm (eelgrass, Zostera marina ) are genetically differentiated at a number of spatial scales. I find also that there is no correspondence between geographic and genetic distances separating subpopulations, an increasingly common result in spatially stratified studies of genetic structure in marine invertebrates. F ‐statistics, calculated for two years from electrophoretic variation at five polymorphic allozyme loci, indicate significant genetic differentiation among sampling quadrats within each of two bays (θ = 0.064‐0.208), between tide zones within a bay (θ = 0.025‐0.157) and between bays (θ = 0.079). Spatial autocorrelation analysis was used to explore genetic differentiation at smaller spatial scales; estimated patch sizes (within which genetic individuals are randomly associated) indicated no appeciable genetic structure at scales less than 20 m × 20 m. Calculated values of F ‐statistics were a function of the spatial scale from which samples were drawn: increasing the size of the “subpopulation” included in calculation of fixation indices for the same “total” sample resulted in an increase in the magnitude of f (e.g., from 0.092 to 0.181) and a decrease in θ (e.g., from 0.186 to 0.025). On the basis of the best estimate of the spatial scale of subpopulations, the effective number of migrants per generation ( N e m ) ranges from 1.1 to 2.8. Genetic consequences of the disturbance regime in the eelgrass habitat sampled were extreme variation between years in the allele richness and proportion of heterozygotes in a sample and a positive relationship between the extinction probability of patches and the genetic variance among them. The changes in F ‐statistics as a function of sampling scale and the observation that θ among sampled quadrats was positively associated with the probability of extinction among quadrats indicated that indirect estimates of gene flow ( N e m ) calculated from θ should be cautiously interpreted in populations that may not yet be in drift‐migration equilibrium.