Slipper limpet males avoid copulating with parasitic castrated females

Discrimination mechanisms that allow males to select female partners are expected to evolve when a significant portion of the female population is sterilized. In this study, we investigated whether males of the slipper limpet species Bostrycapulus odites discriminate between parasitically castrated by a Microphallidae trematode and non-castrated females. We hypothesized that males would prefer healthy females, spend shorter periods on parasitized females, displace longer distances when encountering parasitized females, and abandon females if castrated. Field data revealed that only 7% of the males observed in copulatory positions were on parasitized females. Laboratory experiments confirmed that males primarily select non-parasitized females and exclusively copulate with healthy individuals. The duration of time spent by males on non-parasitized females was almost twice as long as that spent on parasitized females. These results indicate that males bias their mating efforts toward healthy females, and in the few cases where they interact with parasitized females, copulation does not occur. Instead, males spend brief periods on castrated females. Although uncommon in nature, this discriminative ability would be expected to benefit males by enhancing their reproductive success through mating with healthy females.