Effects of intraspecific diversity on survivorship, growth, and recruitment of the eastern oyster across sites

Abstract

Intraspecific diversity, particularly of foundation species, can significantly affect population, community, and ecosystem processes. Examining how genetic diversity relates to demographic traits provides a key mechanistic link from genotypic and phenotypic variation of taxa with complex life histories to their population dynamics. We conducted a field experiment to assess how two metrics of intraspecific diversity (cohort diversity, the number of independent juvenile cohorts created from different adult source populations, and genetic relatedness, genetic similarity among individuals within and across cohorts) affect the survivorship, growth, and recruitment of the foundation species Crassostrea virginica. To assess the effects of both cohort diversity and genetic relatedness on oyster demographic traits under different environmental conditions, we manipulated juvenile oyster diversity and predator exposure (presence/absence of a cage) at two sites differing in resource availability and predation intensity. Differences in predation pressure between sites overwhelmingly determined post-settlement survivorship of oysters. However, in the absence of predation (i.e., cage treatment), one or both metrics of intraspecific diversity, in addition to site, influenced long-term survivorship, growth, and recruitment. While both cohort diversity and genetic relatedness were negatively associated with long-term survivorship, genetic relatedness alone showed a positive association with growth and cohort diversity alone showed a positive association with recruitment. Thus, our results demonstrate that in the absence of predation, intraspecific diversity can affect multiple demographic traits of a foundation species, but the relative importance of these effects depends on the environmental context. Moreover, the magnitude and direction of these effects vary depending on the diversity metric, cohort diversity or genetic relatedness, suggesting that although they are inversely related in this system, each captures sufficiently different components of intraspecific diversity. Given the global loss of oyster reef habitat and rapid decline in oyster population size, our results are particularly relevant to management and restoration. In addition, aquaculture, which commonly excludes predators during early life history stages, may benefit from incorporation of oyster cohort diversity into standard practice.

Genetic diversity and phenotypic variation within hatchery‐produced oyster cohorts predict size and success in the field

“…Similarly, in a prior study using the same oyster cohorts analyzed here, we found higher recruitment of juvenile oysters to experimental assemblages created from four juvenile oyster cohorts (i.e., lines produced in a hatchery from wild stocks) compared to those from only one or two cohorts (Hanley et al. ). Survivorship of juvenile oysters was also associated with decreasing genetic relatedness (Hanley et al.…”

“…These cohorts were used in prior studies to examine the effects of cohort diversity (the number of cohorts) on oyster performance (Hanley et al. ) and the potential for local adaptation across cohorts (Hughes et al. ; Appendix ).…”

Genetic distance predicts trait differentiation at the subpopulation but not the individual level in eelgrass,Zostera marina

“…Furthermore, different metrics of genetic variation appear to have different effects on the outcome of ecological interactions (Abbott et al. 2017; Hanley, Hughes, Williams, Garland & Kimbro, 2016; Jousset et al., 2011), clouding the mechanistic interpretation of the effects of genetic variation in ecology.…”

Genetic diversity of seagrass seeds influences seedling morphology and biomass

“…, Hanley et al. ). For instance, if kin selection operates, then siblings are predicted to have lower competition and higher performance than non‐siblings; alternatively, niche partitioning predicts reduced competition and increased overall performance for non‐siblings compared to siblings (File et al.…”

“…, Hanley et al. ). Life history stage is also often confounded with mode of reproduction: manipulations of plants focus on clonal reproduction, whereas manipulations of invertebrates typically examine sexual reproduction (Aguirre and Marshall ).…”