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Fine-scale population genetic structure of the eastern Pacific bay pipefish, Syngnathus leptorhynchus de Graaf, Ramona Christine

Abstract

Seascapes are complex systems with features that both restrict and enhance dispersal and gene flow among individuals. Understanding factors shaping genetic diversity and genetic population substructure can assist in planning effective conservation areas. Syngnathus leptorhynchus is an eelgrass-dependent fish species ranging from Alaska to Mexico. Pipefish males brood eggs in a specialized brood pouch until their emergence as fully developed young. S. leptorhynchus has a body form that presumably reflects adaptations to mimic Zostera marina L. blades which may, in combination with the provision of prolonged parental care, limit its dispersal potential and promote population subdivision. Syngnathus leptorhynchus were collected from 17 localities iii Barkley Sound, Vancouver Island, British Columbia. A total of 156 alleles were detected with 5 microsatellite loci with an average of 31 (STDV 13.9) alleles per population. Genetic diversity was high and the observed multi-locus heterozygosity was 0.91. Genetic diversity and allelic richness were lowest in North Barkley Sound encompassing the Broken Group Islands, Pacific Rim National Park Reserve (BGI). Pipefish genetic differentiation revealed patterns of local heterogeneity at small spatial scales within the BGI archipelago, but regional homogeneity at larger spatial scales. Genetic differentiation measured over the five loci was weak but statistically significant (Fst = 0.005, P = 0.0001) over a maximum distance between localities of 83 km. Individual pairwise Fst comparisons ranged from 0.00 to 0.017. There was evidence for closed population dispersal consistent with geography and two nascent genetic subpopulations encompassing East Barkley and South/North Barkley Sound. Pipefish at Gibralter Island (BGI) were significantly diverged from other localities. Fjordal environments appeared to restrict pipefish gene flow between the two genetic subpopulations. Archipelagos and deepwater channels restricted pipefish gene flow and increased genetic differentiation. Genetic connectivity of pipefish in localities within the BGI archipelago was restricted and localities were significantly differentiated from each other. Pipefish in two BGI localities, however, revealed unrestricted connectivity and were genetically similar to neighbouring localities outside this oceanographically complex archipelago. Coastal habitats maintain connectivity among pipefish in eelgrass beds located in South/North Barkley Sound and were important in promoting an isolation-by-distance pattern among coastal eelgrass beds. Pipefish genetic neighbourhoods ranged in linear distance from 40-60 kilometres.

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