Genetic by environmental variation but no local adaptation in oysters (Crassostrea virginica)

Abstract

Functional trait variation within and across populations can strongly influence population, community, and ecosystem processes, but the relative contributions of genetic vs. environmental factors to this variation are often not clear, potentially complicating conservation and restoration efforts. For example, local adaptation, a particular type of genetic by environmental (G*E) interaction in which the fitness of a population in its own habitat is greater than in other habitats, is often invoked in management practices, even in the absence of supporting evidence. Despite increasing attention to the potential for G*E interactions, few studies have tested multiple populations and environments simultaneously, limiting our understanding of the spatial consistency in patterns of adaptive genetic variation. In addition, few studies explicitly differentiate adaptation in response to predation from other biological and environmental factors. We conducted a reciprocal transplant experiment of first‐generation eastern oyster (Crassostrea virginica) juveniles from six populations across three field sites spanning 1000 km in the southeastern Atlantic Bight in both the presence and absence of predation to test for G*E variation in this economically valuable and ecologically important species. We documented significant G*E variation in survival and growth, yet there was no evidence for local adaptation. Condition varied across oyster cohorts: Offspring of northern populations had better condition than offspring from the center of our region. Oyster populations in the southeastern Atlantic Bight differ in juvenile survival, growth, and condition, yet offspring from local broodstock do not have higher survival or growth than those from farther away. In the absence of population‐specific performance information, oyster restoration and aquaculture may benefit from incorporating multiple populations into their practices.

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

“…, Hughes et al. ; see Appendix for additional information). These studies used the same experimental design.…”

“…We experimentally evaluated the performance (size, growth, survivorship) of each 2012 juvenile oyster cohort in the field as a function of within-cohort effective allelic diversity. These same oysters were analyzed for different response variables as part of two other studies (Hanley et al 2016, Hughes et al 2017; see Appendix S1 for additional information). These studies used the same experimental design.…”

“…) and the potential for local adaptation across cohorts (Hughes et al. ; Appendix ). In this study, we examined key traits of the broodstock, quantified the genetic diversity of each resulting cohort, compared adult genetic structure to observed juvenile structure, and evaluated links between genetic diversity and performance in the field to inform key knowledge gaps regarding the role of hatcheries in conservation aquaculture.…”

“…In this study, we collaborated with a commercial hatchery to produce multiple cohorts of C. virginica from field-collected broodstock using standard practices. These cohorts were used in prior studies to examine the effects of cohort diversity (the number of cohorts) on oyster performance (Hanley et al 2016) and the potential for local adaptation across cohorts (Hughes et al 2017;Appendix S1). In this study, we examined key traits of the broodstock, quantified the genetic diversity of each resulting cohort, compared adult genetic structure to observed juvenile structure, and evaluated links between genetic diversity and performance in the field to inform key knowledge gaps regarding the role of hatcheries in conservation aquaculture.…”

Biotic interactions affect fitness across latitudes, but only drive local adaptation in the tropics

“…By far the most frequently altered components of the environment were 342 biotic: competition (60 studies via herbicide, weeding, clipping, or planting in tilled gardens or 343 pots), and herbivory/predation (43 studies via fences, cages, and poisons). Only 22 studies paired 344 transplants with experimental manipulations of factors that might cause local adaptation, of 345 which only 10 included a control treatment in an unaltered environment (Thompson et al 1991;346 Kindell et al 1996;Knight and Miller 2004;Sambatti and Rice 2006;Abdala-Roberts and 347 Marquis 2007;Ariza and Tielbörger 2011;Hufford and Mazer 2012;Stanton-Geddes et al 2012;348 Tomiolo et al 2015;Hughes et al 2017). 349…”