Genetic structure of eelgrass Zostera marina meadows in an embayment with restricted water flow

Abstract

Genetic structure of the seagrass Zostera marina in a coastal lagoon with restricted water flow, and with heterogeneous water residence times and oceanographic characteristics, was assessed using 8 polymorphic microsatellite loci. Analyses of genetic differentiation (θ) and Bayesian clustering suggested that the Z. marina population in San Quintin Bay (SQB) is genetically substructured, with at least 4 genetically different groups: (1) West Head, (2) Mouth, (3) East Arm, and (4) East Head. The greatest θ value was observed between the most distant sites (θ = 0.095). The lowest values were found among sites closest to the mouth of the coastal lagoon (θ = 0.000 to 0.009). The maximum likelihood approach showed that the sites at the mouth have a mixed pattern of gene flow without a unidirectional pattern. In contrast, there was a clear pattern of asymmetrical gene flow from the mouth towards the West Head. These results suggested that the restriction of water flow at the heads, current pattern, and the distance between sites can reduce genetic flow and promote genetic differences within Z. marina meadows in small water embayments such as SQB. Though the population is genetically substructured and a 14% decline in cover has been detected, this study did not show evidence of a recent genetic bottleneck. In contrast, mouth sites have experienced a recent expansion in their population size, and also perhaps a recent influx of rare alleles from genetically distinct immigrants.

Edge Effects and the Population Structure of Humboldt Bay, California, Eelgrass (Zostera marinaL.)

“…The surprisingly high mean values of genetic diversity at the plot level of analysis suggest that the spread of clonal genets is limited. This reinforces conclusions elsewhere [13,17] that clonality is not as pervasive as once thought. Relative frequency of genotypes varies widely in the data, with few common types and many scarce types.…”

“…Measures of genetic diversity offer an alternative for the assessment of conservation value in seagrass habitats [43]; results provided here closely match a growing trend in which eelgrass populations are shown to be more genetically diverse than anticipated [17,29,41]. Two similar studies [40,44] empirically tested the role of genetic diversity in a seagrass population's ability to recover from disturbances.…”

“…The microsatellite loci used in this study were all polymorphic with six to eight alleles each (Table 1) and showed a medium to high amount of allelic diversity for an eastern Pacific population of Zostera marina [17,29]. For each locus, there were one or two alleles and genotypes that occurred much more frequently than the others.…”

“…The genetic structure of seagrass populations is likely to reflect these disparate forces. Microsatellite analyses of seagrass populations have demonstrated widely varying genetic diversity between populations [12,13], but it is clear that populations are not the homogenous assemblages of clonal ramets that they were perceived to be [14][15][16][17].…”

Genetic Structure and Diversity of Zostera marina (Eelgrass) in the San Juan Archipelago, Washington, USA

“…Studies employing microsatellite analyses in populations elsewhere (San Francisco Bay, Talbot et al 2004;San Quintin Bay, Muñiz-Salazar et al 2006) have also detected genetic signatures of expansions in populations or components of what may be larger metapopulations of Z. marina, demonstrating fluctuating patch dynamics. For example, Muñiz-Salazar et al (2006) observed a signature of expansion in Z. marina "populations" occupying the mouth of San Quintin Bay, Baja Values are based on analyses of five or more loci (some populations were monomorphic at some loci). Values in bold are significant at P<0.05 (Bonferroni correction applied) a Number of alleles compared b Ratio of heterozygote excess or deficit probabilities (Cornuet and Luikart 1996) c IAM, TPM, SMM = infinite alleles, two-phase and stepwise mutational models of microsatellite evolution, respectively (see text)…”