The effect of sex and mating opportunity on ecological immunity in Brood X cicadas

Catherine M. Hord, Caleb C. Cummings, Frances Anagbonu & Susan N. Gershman. 2024. Ethology Ecology & Evolution, DOI: 10.1080/03949370.2024.2307028. Link to article.

Abstract

Seventeen-year periodical cicadas represent an extreme life history, with individuals spending 17 years as juveniles and less than 45 days as adults. The implications of this life history on investment in immunity are unknown. Using monofilament implants, we examined sex differences in melanization and encapsulation-based immunity in Brood X Magicicada septendecim and M. cassini periodical cicadas. In many insects, females devote more effort to immunity than males which allows females additional time to lay eggs before death. In 17-year cicadas, the functional difference in lifespan between males and females is trivial as compared to their total lifespan. However, we found that in both species, adult females had better immunity (encapsulation response) than males. In both species, male immunity (melanization and encapsulation) declined as they aged, as did female encapsulation. However, female immunity (melanization) either did not decline or improved with age. We conclude that although male immunosenescence resembles that of shorter-lived insects, for females, melanization-based immunity is preserved as they age, potentially due to their unique life history. We also examined whether being housed in mixed-sex versus single-sex enclosures affected immunity but did not find an effect of reproductive opportunity on either melanization or encapsulation in males or females of either species. This is the first study to assay melanization or encapsulation in a cicada, so our results provide a first look at sex- and age-based immunity in this group.