Sexual selection occurs in the aspect of reproduction, and plays an important role in the evolution of diverse morphology and ecology of many species across taxa. There are mainly two mechanisms of sexual selection: one is mate choice, where female preference for a mating partner drives the evolution of male traits, and the other is sexual conflict, where female resistance to copulation drives the antagonistic evolution of male traits (1).
The fundamental discord causing sexual conflict is the amount of investment to copulation. Since copulation is costly, females are adaptive to invest primarily in offspring while males invest primarily in fertilization opportunities. This leads to the conflict over copulation frequency; female fitness is maximized by copulating with one or few males while male prefer multiple copulation (2). However, determining whether multiple copulation is a sexual conflict is difficult because females may be recouping the cost of copulation by trading up with males of superior genetic quality.
To solve this problem, an experimental evolution was conducted using Drosophila melanogaster. The population was reared with different copulation rate according to the eye colour mutation for 5 generations. The frequency of the mutation allele which copulated less often was significantly greater, so multiple copulation of D. melanogaster was certified to be maladaptive to females (3). In D. melanogaster, it is known that seminal fluid proteins harm female such as reducing lifespan (4, 5).
Sexual conflict may lead to further evolution of genetically reduced lifespan.
Male reproductive strategies are typically associated with elevated mortality risks and weaker selection for long lifespan compared to females, due to the high cost of bearing secondary sexual traits and higher extrinsic mortality (6). Therefore, it enables the accumulation of alleles with deleterious effects that are only expressed late in life. In contrast, selection on females prefers low risk and long lifespan because females are limited by the time and energy requirements for offspring production. Analysis in D. melanogaster of lifespan and early-life copulation frequency showed strong negative genetic covariance, indicative of an evolutionary trade-off (7). Multiple copulation in early life time reduces female longevity as mentioned above, which in turn weakens the selection on somatic maintenance in later life and reduces the lifespan.
References
1. Andersson M & Simmons LW (2006) Sexual selection and mate choice. Trends in Ecology & Evolution 21(6):296-302.
2. Holland B & Rice WR (1998) Perspective: Chase-away sexual selection: Antagonistic seduction versus resistance. Evolution 52(1):1-7.
3. Stewart AD, Morrow EH, & Rice WR (2005) Assessing putative interlocus sexual conflict in Drosophila melanogaster using experimental evolution. Proceedings of the Royal Society B-Biological Sciences 272(1576):2029-2035.
4. Wigby S & Chapman T (2005) Sex peptide causes mating costs in female Drosophila melanogaster. Current Biology 15(4):316-321.
5. Sirot LK, Wong A, Chapman T, & Wolfner MF (2015) Sexual Conflict and Seminal Fluid Proteins: A Dynamic Landscape of Sexual Interactions. Cold Spring Harbor Perspectives in Biology 7(2).
6. Vinogradov AE (1998) Male reproductive strategy and decreased longevity. Acta Biotheoretica 46(2):157-160.
7. Travers LM, Garcia-Gonzalez F, & Simmons LW (2015) Live fast die young life history in females: evolutionary trade-off between early life mating and lifespan in female Drosophila melanogaster. Scientific Reports 5.