Potential Role of Strigeid Parasite Infection in the Maintenance of Alternate Reproductive Morphotypes in Bluegill Sunfish (Lepomis macrochirus)

Bluegill sunfish (Lepomis macrochirus) have two male morphotypes, α- and β-males, each differing in appearance and mating strategy. Alpha-males use nest-building tactics, whereas β-males use sneaker or satellite tactics. Lepomis macrochirus are important members of the aquatic community, and are often involved in parasitic life cycles. Among the most common parasites infecting L. macrochirus are strigeids, which include white grub (Posthodiplostomum minimum), black grub (Uvulifer ambloplitis), and yellow grub (Clinostomum marginatum). Previous studies found a higher abundance of strigeid parasites in α-males, even though β-males spend increased time in the littoral zone. One hypothesis is that α-males recruit the parasites during the spawn because of their nest-guarding behavior, which potentially increases their interactions with snail intermediate hosts. To test this hypothesis, L. macrochirus were collected between February and July in consecutive years from 2015 to 2017 from 13 lakes and ponds in northwestern Virginia. The fish were necropsied and all of the endo- and ectoparasites infecting the fish were identified and enumerated. The results supported the hypothesis and showed that α-males had greater infections postspawn, whereas β-males and females had no increase in infection from pre- to postspawn. Additionally, α-males recruited strigeid parasites at a greater rate than β-males, which negatively affected their body condition. The body condition of both α-males and females were negatively affected by P. minimum and U. ambloplitis, but β-males were not affected by either parasite. This shows that the differences in mating strategies between male morphotypes may result in greater strigeid infection in α-males compared with β-males. This may affect the fitness and reproductive output of α-males and be a contributing factor to the maintenance of β-males in the ecologically stable system, despite decreased reproductive success.