DOI: 10.5061/dryad.bg79cnpbw
title: A sterol-mediated gleaner-opportunist trade-off underlies the evolution of grazer resistance to cyanobacteria

description: The human-caused proliferation of cyanobacteria severely impacts consumers
 in freshwater ecosystems. Toxicity is often singled out as the sole trait
 to which consumers can adapt, even though cyanobacteria are not
 necessarily toxic and the lack of nutritionally critical sterols in
 cyanobacteria is known to impair consumers. We studied the relative
 significance of toxicity and dietary sterol deficiency in driving the
 evolution of grazer resistance to cyanobacteria in a large lake with a
 well-documented history of eutrophication and oligotrophication.
 Resurrecting decades-old Daphnia genotypes from the
 sediment allowed us to show that the evolution and subsequent loss of
 grazer resistance to cyanobacteria involved an adaptation to changes in
 both toxicity and dietary sterol availability. The adaptation
 of Daphnia to changes in cyanobacteria abundance
 revealed a sterol-mediated gleaner-opportunist trade-off. Genotypes from
 peak-eutrophic periods showed a higher affinity for dietary sterols at the
 cost of a lower maximum growth rate, whereas genotypes from more
 oligotrophic periods showed a lower affinity for dietary sterols in favor
 of a higher maximum growth rate. Our data corroborate the significance of
 sterols as limiting nutrients in aquatic food webs and highlight the
 applicability of the gleaner-opportunist trade-off for reconstructing
 eco-evolutionary processes. The human-caused proliferation of
 cyanobacteria severely impacts consumers in freshwater ecosystems.
 Toxicity is often singled out as the sole trait to which consumers can
 adapt, even though cyanobacteria are not necessarily toxic and the lack of
 nutritionally critical sterols in cyanobacteria is known to impair
 consumers. We studied the relative significance of toxicity and dietary
 sterol deficiency in driving the evolution of grazer resistance to
 cyanobacteria in a large lake with a well-documented history of
 eutrophication and oligotrophication. Resurrecting decades-old
 Daphnia genotypes from the sediment allowed us to show that the
 evolution and subsequent loss of grazer resistance to cyanobacteria
 involved an adaptation to changes in both toxicity and dietary sterol
 availability. The adaptation of Daphnia to
 changes in cyanobacteria abundance revealed a sterol-mediated
 gleaner-opportunist trade-off. Genotypes from peak-eutrophic periods
 showed a higher affinity for dietary sterols at the cost of a lower
 maximum growth rate, whereas genotypes from more oligotrophic periods
 showed a lower affinity for dietary sterols in favor of a higher maximum
 growth rate. Our data corroborate the significance of sterols as limiting
 nutrients in aquatic food webs and highlight the applicability of the
 gleaner-opportunist trade-off for reconstructing eco-evolutionary
 processes.
description: All data from Figure One are derived from the long-term
 monitoring program of the International Commission for the Protection of
 Lake Constance (IGKB). While the authors have the permission to use and
 publish the data, we do not have the right to upload or share them. Please
 contact the IGKB for acquiring the data.