Male avoidance of parasitized females explained by direct benefits in a pipefish

Abstract

The influence of the parasitic trematode,Cryptocotylesp., on male mate choice in a species of pipefish,Syngnathus typhle, was studied. This parasite induces visible black spots in the skin of pipefish, but cannot be transmitted directly from one pipefish to another. In a mate-choice experiment the males spent more time with females with few or no black spots than with females with many black spots. This result was obtained in experiments with natural variation in parasite load, and also in experiments in which black spots were manipulated using tattoo ink. This suggests that males discriminate against parasitized females by using visual cues. In another choice experiment, males did not show any preference between males with or without black spots, suggesting that the discrimination occurs only in a sexual context. There was a negative correlation between parasite load and female fecundity. As a result, males mating with unparasitized females may benefit directly by fertilizing more eggs.