Costs and benefits of giant sperm and sperm storage organs in Drosophila melanogaster

Abstract

In Drosophila, long sperm are favoured in sperm competition based on the length of the female's primary sperm storage organ, the seminal receptacle (SR). This sperm–SR interaction, together with a genetic correlation between the traits, suggests that the coevolution of exaggerated sperm and SR lengths may be driven by Fisherian runaway selection. Here, we explore the costs and benefits of long sperm and SR genotypes, both in the sex that carries them and in the sex that does not. We measured male and female fitness in inbred lines of Drosophila melanogaster derived from four populations previously selected for long sperm, short sperm, long SRs or short SRs. We specifically asked: What are the costs and benefits of long sperm in males and long SRs in females? Furthermore, do genotypes that generate long sperm in males or long SRs in females impose a fitness cost on the opposite sex? Answers to these questions will address whether long sperm are an honest indicator of male fitness, male post‐copulatory success is associated with male precopulatory success, female choice benefits females or is costly, and intragenomic conflict could influence evolution of these traits. We found that both sexes have increased longevity in long sperm and long SR genotypes. Males, but not females, from long SR lines had higher fecundity. Our results suggest that sperm–SR coevolution is facilitated by both increased viability and indirect benefits of long sperm and SRs in both sexes.

Selecting on age of female reproduction affects lifespan in both sexes and age-dependent reproductive effort in female (but not male) Ceratitis cosyra

“…A tendency to measure reproductive effort mort frequently in females rather than males in these studies might be due to the difficulty of measuring male reproductive investment, but also may reflect complications in understanding how selecting on reproductive scheduling affects males in insect models, given female capacity to store sperm for future fertilisation of eggs (Fritz 2004;Twig and Yuval 2005;Pérez-Staples et al 2007;Schnakenberg et al 2011;Wolfner 2011;Degner and Harrington 2016;Zajitschek et al 2019). Without knowing how often females remate, for how long females store sperm, or the prevailing sperm precedence rules, it becomes challenging to know exactly how selecting on reproductive timing affects males.…”