Sperm economics in males of a neotropical paper wasp

• Grant number: 22/08040-0
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• Start date: November 24, 2022
• End date: December 21, 2022
• Field of knowledge: Biological Sciences - Zoology - Physiology of Recent Groups
• Principal Investigator: André Rodrigues de Souza
• Grantee: André Rodrigues de Souza
• Visiting researcher: Markus Rantala
• Visiting researcher institution: University of Turku, Finland
• Host Institution: Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (FFCLRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Associated research grant: 20/14464-2 - Sexual selection in neotropical social wasps, AP.JP

Abstract

Sexual selection is a major evolutionary force that has been extensively studied in many animals, but social insects are still a notable exception. This is surprising because some peculiar aspects of their reproductive biology allow general principles of sexual selection to be tested in unusual contexts. For example, in male social wasps, spermatogenesis is restricted to the immature stage. Adult males have a fixed amount of sperm that cannot be replenished because testes degenerate a few days after emergence. Nevertheless, males do not die after copulation and therefore can mate multiple times. Male multiple mating is adaptive because not all inseminated females will use sperm (some inseminated females will die before start a new colony, some will start new colonies but behave as subordinate non-reproductive workers). As a result, male social wasps are promisor models to study sperm allocation strategies under the risk of sperm depletion. Theoretical models of sperm economics predict males will adjust investment in sperm production (a costly trait) to maximize their reproductive success, especially if some information about its reproductive prospects is available. For example, cues of high future sperm competition during development may lead to increased investment in testes mass in crickets and moths. However, we know very little about how other factors surrounding mating activity influence the investment in testes in insects. Males of the neotropical eusocial paper wasp Polistes simillimus have sexually dimorphic melanin-based black spots on the face. These visual signals work as sexual ornaments and males with large proportion of face covered on black are preferred by females as mates. The development of these cuticular ornaments is fixed during the immature stage, similar to spermatogenesis. Within a sperm economics framework, we hypothesize that during development, males investing in larger black spots should also invest in larger testes, to compensate for the potentially high sperm demand in adulthood (as they are more attractive, they are likely to mate with more females than the less ornamented males). Thus, this project aims to test if sexy males (e.g. those with more attractive sexual ornaments) make a higher investment in teste size (a proxy for sperm production). (AU)