Population genetic structure of annual and perennial populations ofZostera marinaL. along the Pacific coast of Baja California and the Gulf of California

Abstract

The Baja California peninsula represents a biogeographical boundary contributing to regional differentiation among populations of marine animals. We investigated the genetic characteristics of perennial and annual populations of the marine angiosperm, Zostera marina, along the Pacific coast of Baja California and in the Gulf of California, respectively. Populations of Z. marina from five coastal lagoons along the Pacific coast and four sites in the Gulf of California were studied using nine microsatellite loci. Analyses of variance revealed significant interregional differentiation, but no subregional differentiation. Significant spatial differentiation, assessed using theta(ST) values, was observed among all populations within the two regions. Z. marina populations along the Pacific coast are separated by more than 220 km and had the greatest theta(ST) (0.13-0.28) values, suggesting restricted gene flow. In contrast, lower but still significant genetic differentiation was observed among populations within the Gulf of California (theta(ST) = 0.04-0.18), even though populations are separated by more than 250 km. This suggests higher levels of gene flow among Gulf of California populations relative to Pacific coast populations. Direction of gene flow was predominantly southward among Pacific coast populations, whereas no dominant polarity in the Gulf of California populations was observed. The test for isolation by distance (IBD) showed a significant correlation between genetic and geographical distances in Gulf of California populations, but not in Pacific coast populations, perhaps because of shifts in currents during El Niño Southern Oscillation (ENSO) events along the Pacific coast.

Genetic diversity and connectivity remain high in eelgrass Zostera marina populations in the Wadden Sea, despite major impacts

“…While this will promote strong differentiation at the local scale, connectivity among patchesby incoming dispersal from rafted, fertile seeds -neutralizes this effect. Similar examples of locally high F IS have been found in other European (Olsen et al 2004) and Pacific-Mexican populations (Muniz-Salazar et al 2005) of Z. marina. Alternative explanations for elevated F IS values, such as null alleles, have been ruled out by extensive analyses (Olsen et al 2004), and Wahlund effects, though never completely ruled out, seem unlikely here given, the level of population differentiation observed.…”

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

“…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.…”

“…In analyses of microsatellite loci, awareness of the effect null alleles may have upon results is worthwhile [39]. Like most foundational studies on eelgrass genetics [13,29,40,41], an estimate of null alleles was not employed here. In one study that did estimate the effect of null alleles, Campanella et al [30] found little influence by null alleles upon computed -statistics.…”

Numerous mitigation transplants of the eelgrass Zostera marina in southern California shuffle genetic diversity and may promote hybridization with Zostera pacifica

“…This was not the case. Although only qualitative comparisons of mean  can be made due to differences in normalization and the number of loci used across studies, the mean of 4.78 (Table 1) for the southern California mainland populations is within the estimates of  for Z. marina populations along the US Pacific coast, i.e., San Juan Is, WA (2.74; Wyllie-Echeverria et al, 2010), Bodega Bay, CA (5.81; Olsen et al, 2004), San Francisco Bay (4.29; Ort et al, 2012), and Baja California, Mexico (4.74;Muniz-Salazar et al, 2005). In the global context, where >150 locations have been surveyed worldwide, the highest diversities found with these loci have been in (Pritchard et al, 2000).…”