Males do not always switch females when presented with a better reproductive option

Abstract

Paired individuals are expected to leave their current partner for newly encountered ones of higher quality. In such cases, animals should therefore be able to compare the quality of their current partner to the quality of a new prospective mate next to the couple. We tested this prediction in Gammarus pulex, an amphipod species where paired males have been described to switch females before copulation. Contrary to expectations, a majority of males remained paired to their current female when presented to an unpaired female of higher quality. In fact, males did not seem to compare the quality of the 2 females before switching. They rather based their decision on the quality of their current female only, switching when it was of low quality. We suggest that mate switching functions as a male mate choice strategy under strong competition for female access in G. pulex. Unpaired males may first randomly pair with a female to gather information about its quality as a mate before switching for a new female when the expected quality of unpaired females in the population exceeds that of their current partner.