Population-level food availability affects postcopulatory sexual selection dynamics in the guppy

Postcopulatory sexual selection (PCSS), namely sperm competition and cryptic female choice, is typically investigated in benign environments, with a fixed number of partners, which mate at the same time intervals; all conditions that are rarely met in natural populations.Although there is increasing evidence that environmental fluctuations affect sexual selection before mating, whether and to which extent they influence postcopulatory trajectories is still little explored.PCSS was investigated in replicate populations of guppies (Poecilia reticulata) in which males and females mated after maintained for 2 weeks on either restricted (RE) or ad libitum (AL) diet and the paternity of the offspring produced by multiply mated females was assigned using microsatellite markers.Compared to AL fish, RE females (i) had fewer mating partners, but the time interval between the first and the last mating was not affected; (ii) produced broods with a lower variance in male fertilization success (a measure of the opportunity for PCSS); and (iii) produced broods with a paternity bias towards the first mate (reversing the last sperm precedence observed in AL populations), and associated more towards males with higher courtship rate.Our results demonstrate that short-term limitation in food availability significantly influence PCSS by modifying both fertilization success variance and sperm precedence pattern. Environmental variation should therefore become part of the research paradigm to improve our understanding of postcopulatory evolutionary dynamics.Read the free Plain Language Summary for this article on the Journal blog.