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Sperm competition generates evolution of increased paternal investment in a sex role-reversed seed beetle
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Animal ecology.
2014 (English)In: Journal of Evolutionary Biology, ISSN 1010-061X, E-ISSN 1420-9101, Vol. 27, no 12, 2841-2849 p.Article in journal (Refereed) Published
Abstract [en]

When males provide females with resources at mating, they can become the limiting sex in reproduction, in extreme cases leading to the reversal of typical courtship roles. The evolution of male provisioning is thought to be driven by male reproductive competition and selection for female fecundity enhancement. We used experimental evolution under male- or female-biased sex ratios and limited or unlimited food regimes to investigate the relative roles of these routes to male provisioning in a sex role-reversed beetle, Megabruchidius tonkineus, where males provide females with nutritious ejaculates. Males evolving under male-biased sex ratios transferred larger ejaculates than did males from female-biased populations, demonstrating a sizeable role for reproductive competition in the evolution of male provisioning. Although larger ejaculates elevated female lifetime offspring production, we found little evidence of selection for larger ejaculates via fecundity enhancement: males evolving under resource-limited and unlimited conditions did not differ in mean ejaculate size. Resource limitation did, however, affect the evolution of conditional ejaculate allocation. Our results suggest that the resource provisioning that underpins sex role reversal in this system is the result of male-male reproductive competition rather than of direct selection for males to enhance female fecundity.

Place, publisher, year, edition, pages
2014. Vol. 27, no 12, 2841-2849 p.
Keyword [en]
experimental evolution, fecundity enhancement, Megabruchidius tonkineus, paternal investment, reproductive competition, sex role reversal
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-242014DOI: 10.1111/jeb.12549ISI: 000346280100025PubMedID: 25394675OAI: oai:DiVA.org:uu-242014DiVA: diva2:782293
Available from: 2015-01-20 Created: 2015-01-20 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Sexual selection and the evolution of sex-role reversal in honeylocust beetles
Open this publication in new window or tab >>Sexual selection and the evolution of sex-role reversal in honeylocust beetles
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sexual selection is the prime evolutionary force that makes males and females different. This process has long been viewed as one where male compete with one another and where females choose. However, since the discovery that multiple mating by females is common in animals, sexual selection theory has been expanded to include mate competition between females and mate choice by males. However, empirical studies addressing these themes are scarce. In my thesis, I explore the evolution of sex role reversed mating systems using the honey locust beetles (Megabruchidius dorsalis and M. tonkineus). I used these species to shed light on (1) how closely sexual selection in females resembles its better‑studied male counterpart, (2) the implications of male mating costs for mating system evolution and (3) the effects of reproductive competition between females on the evolution of female courtship behaviour. By manipulating male mating rate, I found that males that mated more lived shorter lives, showing that mating is costly for males. I also demonstrated that males are choosy about whom they mate with and prefer vigorously courting females (Paper II). In contrast to males, previous studies suggested that female honey locust beetles benefit nutritionally from mating due to the large ejaculates provided by males. I manipulated male condition to show that male adult feeding had significant effects on female reproduction. Females that mated with males of good condition lived longer and produced more offspring than females whose mates were in poor condition (Paper III). When mating is costly for males, theory predicts that sexual selection in females can be strong. I compared sexual selection in honey locust beetles to that in two other species of seed beetles with conventional sex roles. I found substantial sexual selection in honey locust beetle females, which was comparable in strength to that in males (Paper I). I also measured the evolutionary effects of altered sex ratios on mating system parameters in both honey locust beetle species, using an experimental evolution design. Under female-biased sex ratios, representing strong sexual selection in females, females of M. dorsalis rapidly evolved elevated courtship intensity, thereby intensifying the reversal of sex roles (Paper V). In M. tonkineus, males evolved under male-biased sex ratios to transfer larger ejaculates, demonstrating the role of male-male reproductive competition for the evolution of male provisioning (Paper IV). My thesis highlights the essential, and often overlooked, role that females play in mating system evolution and that their contribution cannot simply be reduced to mate choice.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 46 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1240
National Category
Evolutionary Biology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:uu:diva-246715 (URN)978-91-554-9209-0 (ISBN)
Public defence
2015-05-13, Zootissalen, Evolutionary Biology Centre, Norbyvägen, Gamla Zoologen (Hus 1), Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2015-04-22 Created: 2015-03-09 Last updated: 2015-07-07

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Fritzsche, KarolineArnqvist, Göran

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