Reduced Genetic Diversity in Eelgrass Transplantations Affects both Population Growth and Individual Fitness

Abstract

The transplantation of eelgrass (Zostera marina) for mitigation results in reduced genetic diversity among individuals and populations in southern California, the Chesapeake Bay, and New Hampshire. Although genetic variation determines the potential for eelgrass to adapt to the rapidly changing environment in its coastal and estuarine habitats, genetic considerations are not currently included in mitigation and restoration policy. I investigated where and how genetic diversity is lost during eelgrass transplantation. I then explored associations between genetic diversity and both vegetative propagation and sexual reproduction to evaluate the importance of genetic diversity for short-term population growth.Eelgrass beds used as donor populations vary in genetic diversity, and some have little or no detectable genetic diversity. Genetic diversity is reduced upon transplantation because donor plants are collected from small areas, leading to random sampling errors in selecting stock. This loss can be minimized by using information from regional surveys of genetic diversity and structure in potential donor populations and by revising donor stock collection.There were significant positive associations between genetic diversity and the sexual reproduction of eelgrass, with a similar trend for vegetative propagation. Individuals heterozygous for glucose-phosphate isomerase (GPI) developed flowering shoots more than did homozygotes. More seeds germinated from a genetically diverse, untransplanted population than from a transplanted population with low genetic diversity. A field transplantation of known multilocus genotypes revealed that leaf shoot density in high-diversity eelgrass increased almost twice as fast as in low-diversity eelgrass over 22 mo. In a mesocosm experiment under heat stress, eelgrass heterozygous for either GPI or malate dehydrogenase (MDH) produced almost twice as many leaf shoots as homozygotes. The difference between treatments in all experiments increased over time. Together, these results imply that there could be economic incentives to planting genetically diverse eelgrass, and that genetic diversity contributes to eelgrass population viability even over the short term.

Ecosystem recovery after climatic extremes enhanced by genotypic diversity

“…The genetic diversity of eelgrass has two clearly defined components: the genomic diversity in a sample of genotypes (24) and the number of genotypes (clones) per area (25). In contrast to previous experiments (26), both components can now be precisely separated by using highresolution molecular markers (27). Here, we use DNA microsatellites that are assumed to be selectively neutral to identify clones (genotypes) for a replicated manipulation of genotypic (clonal) diversity.…”

“…The experiment was conducted by using SCUBA in a water depth of 1.6-1.8 m. At our high-latitude study site, growth of macrophytes is highly seasonal and confined to MaySeptember. Thus, our experimental period from May 16 through Sep. 26,2003, covered almost the complete growing season. To identify donor genotypes, we set up a marked grid of 10 m ϫ 9.3 m in the vicinity (Ͻ20 m distance) of the experimental site in mid-April 2003.…”

Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance

“…In addition to enhancing estuarine primary productivity, Zostera provides habitat for numerous fishes and invertebrates and plays a role in nutrient cycling and sediment stabilization (20). Habitat fragmentation resulting from human activities and subsequent restoration practices have led to local-scale declines in seagrass genetic diversity, but the consequences of these declines for the ecosystem services provided by eelgrass remain unclear (21).…”

Genetic consequences of a century of protection: serial founder events and survival of the little spotted kiwi (Apteryx owenii)

“…This is because population growth rates may be reduced following a bottleneck, but remain positive. Thus, a small population exhibiting reduced genetic diversity and suffering substantial inbreeding depression may still be growing in size [6,63], and growing populations with large census sizes might still be suffering reduced fitness owing to low genetic diversity and inbreeding [64]. Both of these scenarios describe rspb.royalsocietypublishing.org Proc R Soc B 280: 20130576 populations that are vulnerable to changing environments and stochastic events.…”

“…Demographic dynamics relative to loss of genetic diversity are complex and difficult to predict. Many populations have grown in size following extreme losses of genetic variation [6,63,64]. This is because population growth rates may be reduced following a bottleneck, but remain positive.…”