Egg hatching in the cestode Schistocephalus solidus shows no evidence of quorum sensing

Abstract

Schistocephalus solidus is a parasitic cestode with a complex, multi-host life cycle. S. solidus reproduces in its terminal host either by exchanging gametes with similarly sized individuals or selfing. Fertilized eggs then pass through the feces of the host and hatch at the bottom of freshwater lakes. Previous work found that selfing greatly depresses egg hatching rates, presumably as a result of inbreeding depression. We predicted that S. solidus may have evolved quorum sensing (QS) during hatching as a mechanism to facilitate synchronized infection, thereby increasing the opportunity for outcrossing in its terminal host. We tested whether density-dependent hatch rates were present across three parasite populations, examining both outcrossed and selfed progeny. We predicted that if QS was present, it would be common across all populations, and that increasing egg density would result in higher hatching rates. We also expected that outcrossed eggs would hatch at higher rates than those produced via selfing. While we found different hatching rates between populations, there was no effect of egg density. Selfed eggs did hatch at significantly lower rates than outcrossed eggs, replicating previous findings. Although we failed to find density dependent hatching in our limited sample, we conclude by discussing the conditions in which QS may evolve in isolated S. solidus populations.