Resurrection genomics provides molecular and phenotypic evidence of rapid adaptation to salinization in a keystone aquatic species

Abstract

Ecologists and evolutionary biologists are increasingly cognizant of rapid adaptation in wild populations. Rapid adaptation to anthropogenic environmental change is critical for maintaining biodiversity and ecosystems services into the future. Anthropogenic salinization of freshwater ecosystems is quickly emerging as a primary threat, which is well documented in the northern temperate ecoregion. Specifically, many northern temperate lakes have undergone extensive salinization because of urbanization, including increased impervious surfaces for runoff, and the extensive use of road deicing salts (e.g., NaCl). It remains unclear if increasing salinization will lead to extirpation of species from these systems. Using a "resurrection genomics" approach, we investigated whether the keystone aquatic herbivore, Daphnia pulicaria, has evolved increased salinity tolerance in a severely salinized lake located in Minnesota, USA. Whole genome resequencing of 54 Daphnia clones hatched from resting eggs that represent a 25-year temporal contrast demonstrates that many regions of the genome containing genes related to osmoregulation are under selection in the study population. Tolerance assays of clones revealed that the most recent clones are more tolerant to salinity than older clones; this pattern is concomitant with the temporal pattern of increasing salinity in this lake. Together, our results demonstrate that keystone species such as Daphnia can rapidly adapt to increasing freshwater salinization. Further, our results indicate that rapid adaptation to salinity may allow lake Daphnia populations to persist in the face of anthropogenic salinization maintaining the food webs and ecosystem services they support despite global environmental change.

The ecosystem implications of road salt as a pollutant of freshwaters

“…Some shifts in salt tolerance may be attributed to genomic changes related to osmoregulation. Studying a population of Daphnia pulicaria through a 25‐year period of increasing salinity, Wersebe and Weider (2022) found the population evolved higher salinity tolerance over time. Genome sequencing revealed signatures of natural selection that were associated with genes related to osmoregulation, and found mutations in a gene that encodes a key chloride channel protein.…”