Walsh, M. R. | bioRxiv Science

bioRxiv2025

Experimental rewilding of stickleback drives phenotypic shifts that oppose long-term evolutionary trajectories in Daphnia in Alaskan lakes

Trophic rewilding restores top-down interactions and may, in turn, drive novel patterns of evolutionary change. Predatory Northern pike invaded lakes in Alaska and eliminated native fish fauna. In 2018, pike were extirpated to reset these ecosystems. Contrasting trophic ecomorphs (benthic vs. limnetic) of three-spine stickleback were then re-introduced as part of whole-lake rewilding experiments. We examined the top-down effects of stickleback on phenotypic change in Daphnia over three years in lakes that naturally contained sticklebacks and compared such trends with the experimental lakes. We observed consistent phenotypic differences between lakes with naturally occurring populations of benthic vs. limnetic stickleback. The patterns of phenotypic divergence indicate that predatory selection is stronger on Daphnia in lakes with benthic stickleback. The trends in the experimental lakes were temporally variable and opposed the trends observed in natural lakes. Rewilding provides insights into the inconsistencies that can manifest between short- and long-term influences of natural selection.

evolutionary biology↗

bioRxiv2023

A resurrection ecology test for the effects of ionizing radiation and other environmental correlates on Daphnia evolution

Acute exposure to ionizing radiation has well-documented, immediate negative consequences for individuals. However, the evolutionary consequences for populations exposed to ionizing radiation is unclear. For example, a meta-analysis of taxa exposed to Chernobyl fallout found some evidence for elevated mutation rates in animal and plant taxa; however, in people, de novo mutation rates in offspring of parents exposed to radiation during and after the Chernobyl accident were no higher than controls. Furthermore, whether irradiation and increased mutation rates drive adaptation to radiation also has mixed support. Ambiguity in both cases likely arises from the difficulty of studying mutation rates and adaptation after rare nuclear events whose ionizing radiation is distributed heterogeneously in time and space. Here, we report an attempt to better address this difficulty with a "resurrection ecology" study of Daphnia spp. in Utah lakes that experienced nuclear fallout from US Department of Energy weapons testing in the 1950s and 1960s. The idea was to recover dormant Daphnia eggs from sediment cores that spanned the nuclear testing era in the American West. We predicted that survival and fecundity of eggs hatched in the lab would show fitness declines correlated with ionizing radiation fallout and a potential recovery once nuclear testing stopped. We successfully obtained multiple cores from three lakes that dated back to the 1800s. We isolated >4700 dormant eggs from those cores, spanning the nuclear era, but were only able to hatch a single egg in the lab. Thus, we could not conduct life history experiments to test our prediction. The purpose of this manuscript, therefore, is to describe the study and make our radioisotope core dating and sedimentation data available to other paleolimnological researchers. We also report a side study of stable isotope change through time measured from dormant eggs and the sediment.

evolutionary biology↗