Local adaptation in a marine foundation species: Implications for resilience to future global change

Abstract

Environmental change is multidimensional, with local anthropogenic stressors and global climate change interacting to differentially impact populations throughout a species’ geographic range. Within species, the spatial distribution of phenotypic variation and its causes (i.e., local adaptation or plasticity) will determine species’ adaptive capacity to respond to a changing environment. However, comparatively less is known about the spatial scale of adaptive differentiation among populations and how patterns of local adaptation might drive vulnerability to global change stressors. To test whether fine‐scale (2–12 km) mosaics of environmental stress can cause adaptive differentiation in a marine foundation species, eelgrass (Zostera marina), we conducted a three‐way reciprocal transplant experiment spanning the length of Tomales Bay, CA. Our results revealed strong home‐site advantage in growth and survival for all three populations. In subsequent common garden experiments and feeding assays, we showed that countergradients in temperature, light availability, and grazing pressure from an introduced herbivore contribute to differential performance among populations consistent with local adaptation. Our findings highlight how local‐scale mosaics in environmental stressors can increase phenotypic variation among neighboring populations, potentially increasing species resilience to future global change. More specifically, we identified a range‐center eelgrass population that is pre‐adapted to extremely warm temperatures similar to those experienced by low‐latitude range‐edge populations of eelgrass, demonstrating how reservoirs of heat‐tolerant phenotypes may already exist throughout a species range. Future work on predicting species resilience to global change should incorporate potential buffering effects of local‐scale population differentiation and promote a phenotypic management approach to species conservation.

A Pleistocene legacy structures variation in modern seagrass ecosystems

“…Genetic diversity within foundation species often strongly influences associated ecosystems ( 34 ), including eelgrass ( 35 ), where trait diversity underlies these effects ( 36 ). And eelgrass shows remarkable capacity for local adaptation to variation in conditions ( 21 , 37 – 39 ), as do other foundation species ( 7 ). However, the ecosystem-level consequences of genetic variation have not previously been addressed at the global scale nor linked to biogeographic history as done here.…”

Disease surveillance by artificial intelligence links eelgrass wasting disease to ocean warming across latitudes

“…Given the spread in local temperatures across the study range (Supporting Information Fig. S2), and the likely adaptation of eelgrass populations to local temperature regimes (Beca‐Carretero et al 2018; King et al 2018; DuBois et al 2022), we also calculated relative metrics of anomalies above long‐term mean and 90 th percentile temperatures. Long‐term temperatures were based on 11‐d rolling averages over the 9‐yr period of available SST (Hobday et al 2016).…”

Environment predicts seagrass genotype, phenotype, and associated biodiversity in a temperate ecosystem

“…Elsewhere, it has been found that Z. marina population genetics differ along a salinity gradient ( Martínez-García et al, 2021 ) and that isolated locations such as fjords can harbor distinct genotypes ( Olsen et al, 2013 ). It is also known from reciprocal transplant and common garden experiments that local Z. marina populations can show a “home-site advantage” at scales of a few kilometers ( Hämmerli and Reusch, 2002 ; DuBois et al, 2022 ). Therefore, it may not be surprising to find seagrass genotypes selected for estuarine environments, and studies like ours, based on microsatellites, will hopefully provide support for whole genome approaches designed to investigate adaptation and selection.…”