Behavioral Avoidance Response of Daphnia to Fungal Infection Caused by Metschnikowia Species in a Temperate Reservoir.

Abstract

Simple SummaryThe negative effects of fungal infection on the survival and reproduction of cladocerans, a representative prey community in freshwater, are unexplored. In this study, we hypothesized that the winter migration pattern of Daphnia pulicaria, observed in the Anri Reservoir in South Korea, is the host’s defense response to fungal infection. Daphnia pulicaria was mainly distributed in the central bottom layer of the reservoir before winter (summer to autumn) but migrated to the littoral area during winter as fungal infections in the communities gradually spread in the bottom region. However, when the spread of infection was low, D. pulicaria did not migrate. The migrated individuals with dormant eggs were mostly infected and are believed to have migrated to the littoral area to freeze their dormant eggs. We found that dormant eggs of D. pulicaria obtained from ice crystals had lower hatching and infection rates than dormant eggs obtained adaptively in Daphnia mothers. Such a strategy is an efficient response of D. pulicaria to avoid the spread of fungal infection in communities and to maintain their continuous population growth.Morphological or behavioral defense mechanisms are important evolutionary strategies for the survival of prey. Studies have focused on predation and competition, but infection has been overlooked, despite being a determining factor of distribution and species diversity of prey. We hypothesized that the winter migration of Daphnia pulicaria is a community defense strategy to avoid fungal infection. To test this hypothesis, environmental variables and the Cladocera community, including D. pulicaria, were monitored in three study sections of the Anri Reservoir in the Republic of Korea during September 2010–August 2015. During three winter seasons, the density of infected D. pulicaria increased in all study sections, and they migrated from the central to the littoral area. Most of the infected individuals had dormant eggs in sexually reproducing mothers. However, when the proportion of non-infected individuals was higher than that of infected individuals, winter migration was not observed. Additional microcosm experiments showed that dormant eggs of D. pulicaria obtained from ice crystals in the littoral area had lower hatching and infection rates than those obtained from mothers moving from other zones. Therefore, the migration of D. pulicaria during winter is an active response to avoid intergenerational fungal infection.