Reproductive Trade-Offs Between Costly Sexually Selected Weapons and Other Expensive Tissues in Three Species of Coreoidea

Student: Anna Schill ’22
Research Mentors: Christine Miller and Michael Forthman (University of Florida Department of Entomology)

Reproduction takes up a lot of an organism’s energy via vigorous competition over mates, growing reproductive organs, and raising offspring. Our study used leaf footed bugs which invest a lot of energy in elaborate hind legs for competition. We examined the extent to which males and females had to shrink their gonads when the investment in their hind leg weapons was artificially increased by adding extra weight.

Organisms generally have a finite pool of resources available for necessary functions such as survival, growth, and reproduction; they cannot always invest completely in each functional group, thus investing energy into one means having less for another. Within these functional groups, such as reproduction, further trade-offs are expected to exist, e.g., between costly primary sexual traits (testes or gametes) responsible for fertilization success and secondary sexual traits (ornaments or weapons) responsible for securing mating opportunities. Previous studies have shown that sexually selected weapons in males can be expensive to develop and maintain and trade off with testes size. One emerging model in these studies are leaf-footed bugs (Insecta: Hemiptera: Coreidae), which have elaborate, costly hind leg weapons that can be self-amputated when entrapped; losing these weapons are associated with increased investment in gonads. Furthermore, this relationship between hind leg mass and gonad mass is seen in weaponless females, adding a layer of complexity to the system. However, it is unknown if increasing the cost of the hind leg will result in decreased investment in the gonads. Using Leptoglossus zonatus (Dallas, 1852), we hypothesized that increasing the cost of a weapon during development would cause gonads of both sexes to be smaller because more resources would be required to develop and maintain a heavier weapon. In our experiment, we added weights to the hind legs of late stage juveniles and measured gonad, weapon, and body mass when they reached sexual maturity as adults. The results of this study will complement previous work investigating resource allocation decisions during development and will provide insights on competition for resources between costly sexual traits.