Delayed virulence and limited costs promote fecundity compensation upon infection

Individuals invest limited resources across vital tasks such as reproduction and survival. Individuals can spread reproductive investment over their lifetime, but cues of death or reduced fitness can influence this investment. In some systems, cues of infection induce early but costly reproduction through fecundity compensation as future reproduction becomes uncertain. A key aspect of parasite biology is the delay between exposure to parasites and the onset of virulence. This creates an important window of opportunity for hosts to respond to infection. Existing models have not accounted for this delay or the costs borne by offspring. We combine a theoretical and experimental approach to assess the role of costs and the importance of delay in virulence on fecundity compensation. We find that a delay in virulence selects for plastic fecundity responses even with moderate offspring costs. We tested our model experimentally by exposing pea aphids, Acyrthosiphon pisum, to various ecologically relevant cues of infection and monitored lifetime reproduction and survival of these aphids and their offspring. Our challenges induced fecundity compensation, but we did not detect any costs in mothers or offspring. We predict that the relationship between the costs and the delay in onset of virulence, as found here, determines the success of fecundity compensation as an adaptation against parasitism.