Assessing the Potential for an Ongoing Arms Race Within and Between the Sexes: Selection and Heritable Variation

Abstract

In promiscuous species, sexual selection generates two opposing male traits: offense (acquiring new mates and supplanting stored sperm) and defense (enforcing fidelity on one's mates and preventing sperm displacement when this fails). Coevolution between these traits requires both additive genetic variation and associated natural selection. Previous work with Drosophila melanogaster found autosomal genetic variation for these traits among inbred lines from a mixture of populations, but only nonheritable genetic variation was found within a single outbred population. These results do not support ongoing antagonistic coevolution between offense and defense, nor between either of these male traits and female reproductive characters. Here we use a new method (hemiclonal analysis) to study genomewide genetic variation in a large outbred laboratory population of D. melanogaster. Hemiclonal analysis estimates the additive genetic variation among random, genomewide haplotypes taken from a large, outbred, locally adapted laboratory population and determines the direction of the selection gradient on this variation. In contrast to earlier studies, we found low but biologically significant heritable variation for defensive and offensive offspring production as well as all their components (P1, fidelity, P2, and remating). Genetic correlations between these traits were substantially different from those reported for inbred lines. A positive genetic correlation was found between defense and offense, demonstrating that some shared genes influence both traits. In addition to this common variation, evidence for unique genetic variation for each trait was also found, supporting an ongoing coevolutionary arms race between defense and offense. Reproductive conflict between males can strongly influence female fitness. Correspondingly, we found genetic variation in both defense and offense that affected female fitness. No evidence was found for intersexual conflict in the context of male defense, but we found substantial intersexual conflict in the context of male offensive sperm competitive ability. These results indicate that conflict between competing males also promotes an associated arms race between the sexes.

The Roles of Natural and Sexual Selection During Adaptation to a Novel Environment

“…In addition, four individual CHCs are positively correlated with wing length (an index of body size) in a field population, suggesting that their expression may be condition dependent . The above results, suggestive of goodgenes mate choice, contrast with those from D. melanogaster that suggest a mate choice system dominated by strong sexual conflict (e.g., Rice 1996;Holland and Rice 1999;Brown et al 2004;Wigby and Chapman 2004;Friberg et al 2005;Lew and Rice 2005;Orteiza et al 2005;Stewart et al 2005).…”

Assessing sexual conflict in theDrosophila melanogasterlaboratory model system

“…The observed negative slope between female remating rate and female lifetime fecundity demonstrated that selection favours female that are more resistant to persistent male courtship. Another similar study by Friberg et al (2005) focusing on selection in males demonstrated that the selection gradient on male remating rate, not surprisingly, is positive. Taken together, these two studies demonstrate that males are currently being selected to remate females at higher rate, and females to remate at lower rate, so that evolutionary advance by males (i.e.…”

“…In each treatment males and females were reared under the normal culturing protocol of the LH M base population with the exception of the phenocopy procedure used to control body size body size, and that they were collected as virgin soon after eclosion and held in separate, samesex vials until the beginning of the adult-competition stage of their life cycle (see above), at which point they were placed at normal density in the bisected culturing vials. Females were mated immediately before being placed in the adult-competition vials (by placing them for 90 min with a 50% excess of males) and remating in the adult-competition vials was measured using genetic markers (see Friberg et al 2005;Orteiza et al 2005, for a description of the genetic marker system). The two treatments were: (i) a lowresource refuge (as occurs in nature): males were confined to the side of the vial containing the live yeast needed for high female fecundity, and (ii) a wide-mesh control in which both males and females could pass through the mesh.…”

The androgen receptor and prostate cancer: A role for sexual selection and sexual conflict?

“…Sexual conflict can occur in several different ways, including intragenomic conflict, intergenomic (or interlocus) conflict, and intersexual ontogenetic conflict [4,5]. Recent evidence suggests that these forms of genetic conflict are common [5,6].…”