Population structure and genetic variation of lane snapper (<Emphasis Type="Italic">Lutjanus synagris</Emphasis>) in the northern Gulf of Mexico |
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Authors: | S Karlsson E Saillant J R Gold |
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Institution: | (1) Center for Biosystematics and Biodiversity, Texas A&M University, College Station, TX 77843-2258, USA |
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Abstract: | Lane snappers (Lutjanus synagris), sampled from eight localities in the northern Gulf of Mexico (Gulf) and one locality along the Atlantic coast of Florida,
were assayed for allelic variation at 14 nuclear-encoded microsatellites and for sequence variation in a 590 base-pair fragment
of the mitochondrially encoded ND-4 gene (mtDNA). Significant heterogeneity among the nine localities in both microsatellite
allele and genotype distributions and mtDNA haplotype distributions was indicated by exact tests and by analysis of molecular
variance (AMOVA). Exact tests between pairs of localities and spatial analysis of molecular variance (SAMOVA) for both microsatellites
and mtDNA revealed two genetically distinct groups: a Western Group that included six localities from the northwestern and
northcentral Gulf and an Eastern Group that included three localities, one from the west coast of Florida, one from the Florida
Keys, and one from the east (Atlantic) coast of Florida. The between-groups component of molecular variance was significant
for both microsatellites (Φ
CT = 0.016, P = 0.009) and mtDNA (Φ
CT = 0.208, P = 0.010). Exact tests between pairs of localities within each group and spatial autocorrelation analysis did not reveal genetic
heterogeneity or an isolation-by-distance effect among localities within either group. MtDNA haplotype diversity was significantly
less (P < 0.0001) in the Western Group than in the Eastern Group; microsatellite allelic richness and gene diversity also were significantly
less in the Western Group (P = 0.015 and 0.013, respectively). The difference in genetic variability between the two groups may reflect reduced effective
population size in the Western Group and/or asymmetric rates of genetic migration. The relative difference in variability
between the two groups was substantially greater in mtDNA and may reflect one or more mtDNA selective sweeps; tests of neutrality
of the mtDNA data were consistent with this possibility. Bayesian analysis of genetic demography indicated that both groups
have experienced a historical decline in effective population size, with the decline being greater in the Western Group. Maximum-likelihood
analysis of microsatellite data indicated significant asymmetry in average, long-term migration rates between the two groups,
with roughly twofold greater migration from the Western Group to the Eastern Group. The difference in mtDNA variability and
the order-of-magnitude difference in genetic divergence between mtDNA and microsatellites may reflect different demographic
events affecting mtDNA disproportionately and/or a sexual and/or spatial bias in gene flow and dispersal. The spatial discontinuity
among lane snappers in the region corresponds to a known zone of vicariance in other marine species. The evidence of two genetically
distinct groupings (stocks) has implications for management of lane snapper resources in the northern Gulf. |
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