Limited potential for adaptation to climate change in a broadly distributed marine crustacean

TLDR

The extent to which acclimation and genetic adaptation can buffer natural populations against climate change is largely unknown, and most models assume homogeneous climatic envelopes despite limited empirical data on intraspecific genetic variation in tolerance traits. The study tests the extent of thermal tolerance variation in Tigriopus californicus across eight populations spanning over 17° of latitude using laboratory rearing and selection experiments. Laboratory rearing and selection experiments quantified thermal tolerance and adaptation potential across these populations. Tigriopus californicus shows strong local temperature adaptation, with less than 1 % of thermal tolerance variance within populations, and heat‑tolerant phenotypes from low latitudes cannot be achieved in high‑latitude populations even after acclimation or ten generations of selection, indicating limited plasticity and adaptation to buffer against rising temperatures.

Abstract

The extent to which acclimation and genetic adaptation might buffer natural populations against climate change is largely unknown. Most models predicting biological responses to environmental change assume that species' climatic envelopes are homogeneous both in space and time. Although recent discussions have questioned this assumption, few empirical studies have characterized intraspecific patterns of genetic variation in traits directly related to environmental tolerance limits. We test the extent of such variation in the broadly distributed tidepool copepod Tigriopus californicus using laboratory rearing and selection experiments to quantify thermal tolerance and scope for adaptation in eight populations spanning more than 17° of latitude. Tigriopus californicus exhibit striking local adaptation to temperature, with less than 1 per cent of the total quantitative variance for thermal tolerance partitioned within populations. Moreover, heat-tolerant phenotypes observed in low-latitude populations cannot be achieved in high-latitude populations, either through acclimation or 10 generations of strong selection. Finally, in four populations there was no increase in thermal tolerance between generations 5 and 10 of selection, suggesting that standing variation had already been depleted. Thus, plasticity and adaptation appear to have limited capacity to buffer these isolated populations against further increases in temperature. Our results suggest that models assuming a uniform climatic envelope may greatly underestimate extinction risk in species with strong local adaptation.