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Assessing the potential for an ongoing arms race within and between the sexes: selection and heritable variation
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2005 (English)In: Evolution, ISSN 0014-3820, E-ISSN 1558-5646, Vol. 59, no 7, 1540-1551 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Lawrence, Kans.: Society for the Study of Evolution , 2005. Vol. 59, no 7, 1540-1551 p.
Keyword [en]
Coevolution, Drosophila melanogaster, interlocus intersexual conflict, interlocus intrasexual conflict, sexual selection, sperm competition
URN: urn:nbn:se:umu:diva-5012DOI: 10.1111/j.0014-3820.2005.tb01803.xPubMedID: 16153039OAI: diva2:144355
Available from: 2006-03-30 Created: 2006-03-30 Last updated: 2011-03-25Bibliographically approved
In thesis
1. Sexual conflict and male-female coevolution in the fruit fly
Open this publication in new window or tab >>Sexual conflict and male-female coevolution in the fruit fly
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Harmony and cooperation was for long believed to dominate sexual interactions. This view slowly started to change 25 years ago and is today replaced with a view where males and females act based on what is best from a costs-benefits perspective. When sex specific costs and benefits differ, concerning reproductive decision influenced by both sexes, sexual conflict will occur. The basis for discordant reproductive interests between the sexes is that males produce many small gametes, while females’ produce few and large gametes. One result of this difference is that the optimal mating rate differs between the sexes. Males, with their many small sperm, maximize their reproductive output by mating with many females, while females often do best by not mating more frequently than to fertilize their eggs, since mating often entails a cost. Sexual conflict over mating is thus an important factor shaping the interactions between the sexes. In this thesis I study this and related conflicts between the sexes, using mathematical models, fruit flies and comparative methods. Mathematical modelling was used to explore how males and females may coevolve under sexual conflict over mating. This model shows that sexual conflict over mating results in the evolution of costly female mate choice, in terms high resistance to matings, and costly exaggerated male sexual traits, aimed to manipulate females into mating. A key assumption in this model is that males which females find attractive also are more harmful to females. This assumption was tested by housing fruit fly females with either attractive or unattractive males. Females kept with attractive males were courted and mated more, and suffered a 16 percent reduction in lifetime offspring production. In another study I measured genetic variation in two antagonistic male traits used to compete over females; offence - a male’s ability to acquire new mates and supplant stored sperm, and defence - a male’s ability to induce fidelity in his mates and prevent sperm displacement when remating occurs. Independent additive genetic variation and positive selection gradients were found for both these traits, indicating an ongoing arms race between these male antagonistic traits. This arms race also had a negative impact on females, since high values of offence compromised female fitness. Genetic variation in female ability to withstand male harm was also tested for and found, indicating that females evolve counter adaptations to reduce the effect of harmful male traits. Finally, the proposed link between sexual conflict and speciation was tested. Theory suggests that perpetual sexual arms races will cause allopatric populations to evolve along different evolutionary trajectories, resulting in speciation. This theory was tested using comparative methods by contrasting the number of extant species in taxa with high and low opportunity for sexual conflict. The study showed that taxa with high opportunity for sexual conflict, on average, has four times as many species as those with low opportunity, supporting that sexual conflict is a key process in speciation.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap, 2006. 22 p.
cryptic male mate choice, Drosophila melanogaster, female mate choice, multiple mating, sexual conflict, sexually antagonistic coevolution, sexual selection, speciation, sperm competition
National Category
Biological Sciences
urn:nbn:se:umu:diva-735 (URN)91-7264-055-3 (ISBN)
Public defence
2006-04-20, KB3 A9, KBC-huset, Umeå, 10:00
Available from: 2006-03-30 Created: 2006-03-30Bibliographically approved

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