Male copulatory guarding enhances female foraging in a water strider

Summary

In the laboratory, females of Gerris remigis foraging singly after being separated from a copulating male averaged 16 times longer to repel male copulatory attempts compared to repelling time when copulating (60 trials). In<10 min after separation, all females either became immobile at the edge (in 34% of all trials), or recopulated and either continued to forage (61%) or swam to the edge and became immobile (5%). Copulating females captured 85% of imitation prey, but single females, harassed by males, captured only 32% of prey.

During a census of 2 small streams, in the pools with swimming single males, >99% of all swimming females were copulating, <1% being single. Ninety seven percent of all single females were immobile at the edge, whereas only 11% of all pairs were at the edge. In pools without swimming single males, 32% of all single females were swimming, compared to <1% in pools with swimming males. Introductions of a male into 4 pools with a female swimming singly in each resulted in the females either becoming immobile at the edge or copulating. The 2 streams had a ♂:♀ sex ratio of 1.6:1, and 79% of all females were copulating during the census. Foraging, copulation and copulatory attempts continued at a reduced level during the night.

Thus in streams where male G. remigis are attempting to copulate, females can forage effectively only by carrying a copulating male who apparently repels copulatory attempts by other males.