Life history shifts in an exploited African fish following invasion by a castrating parasite.

Evolutionary theory predicts that infection by a parasite that reduces future host survival or fecundity should select for increased investment in current reproduction. In this study, we use the cestode and its intermediate fish host in Wissman Bay, Lake Nyasa (Tanzania), as a model system. Using data about infection of fish hosts by collected for a period of 10 years, we explored whether parasite infection affects the fecundity of the fish host , and whether host reproductive investment has increased at the expense of somatic growth. We found that had a strong negative effect on the fecundity of its intermediate fish host. For the noninfected fish, we observed an increase in relative gonadal weight at maturity over the study period, while size at maturity decreased. These findings suggest that the life history of has been shifting toward earlier reproduction. Further studies are warranted to assess whether these changes reflect plastic or evolutionary responses. We also discuss the interaction between parasite and fishery-mediated selection as a possible explanation for the decline of stock in the lake.