DO TRADE-OFFS BETWEEN PRE- AND POSTCOPULATORY INVESTMENT OCCUR IN GUPPIES (POECILIA RETICULATA) WHEN DIET IS RESTRICTED AND COURTSHIP IS FORCED?

Abstract

In polyandrous species, sexual selection acts both before (precopulatory) and after (postcopulatory) mating on traits that are important for reproductive success. Precopulatory traits are important for mate acquisition and include weapons and ornaments. Postcopulatory traits include components of sperm quantity and quality, which determine a male’s fertilization success in the presence of sperm from other males. Sperm competition theory predicts trade-offs between investment in pre- and postcopulatory traits since reproductive traits are energetically costly and the amount of energy available for investment is typically fixed. However, evidence for this theory is mixed and few studies have experimentally examined whether resource limitation, together with forced precopulatory investment yield trade-offs between investment in pre- and postcopulatory sexually selected traits. In this study I examine whether manipulations of diet quantity and courtship investment expose trade-offs between investment in pre- and postcopulatory traits in guppies (Poecilia reticulata). I accomplish this by comparing behavioral, ornamental, and sperm characteristics between males assigned at random to restricted or ad libitum diet treatments, with or without visual contact with females, while controlling for genetic background. My results show that certain precopulatory traits (sigmoid courtship display rate and standard body area) and postcopulatory traits (sperm viability, sperm flagellum and sperm midpiece length, and sperm number) are more sensitive to manipulations in diet quantity and courtship investment. Additionally, these results, to the best of my knowledge, are the first to reveal some evidence for phenotypic trade-offs between investment in precopulatory traits (sperm viability and sperm flagellum length) and postcopulatory traits (sexual interest); this is consistent with the predictions of sperm competition theory and suggests that trade-offs predicted by this theory may be revealed when diet is limiting and courtship is forced.