Sexual selection and the evolution of sex-role reversal in honeylocust beetles

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 h...

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Main Author: Fritzsche, Karoline
Format: Doctoral Thesis
Language:English
Published: Uppsala universitet, Zooekologi 2015
Online Access:http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-246715
http://nbn-resolving.de/urn:isbn:978-91-554-9209-0
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spelling ndltd-UPSALLA1-oai-DiVA.org-uu-2467152015-07-08T04:51:00ZSexual selection and the evolution of sex-role reversal in honeylocust beetlesengFritzsche, KarolineUppsala universitet, ZooekologiUppsala2015Sexual 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. Doctoral thesis, comprehensive summaryinfo:eu-repo/semantics/doctoralThesistexthttp://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-246715urn:isbn:978-91-554-9209-0Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 1240application/pdfinfo:eu-repo/semantics/openAccess
collection NDLTD
language English
format Doctoral Thesis
sources NDLTD
description 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.
author Fritzsche, Karoline
spellingShingle Fritzsche, Karoline
Sexual selection and the evolution of sex-role reversal in honeylocust beetles
author_facet Fritzsche, Karoline
author_sort Fritzsche, Karoline
title Sexual selection and the evolution of sex-role reversal in honeylocust beetles
title_short Sexual selection and the evolution of sex-role reversal in honeylocust beetles
title_full Sexual selection and the evolution of sex-role reversal in honeylocust beetles
title_fullStr Sexual selection and the evolution of sex-role reversal in honeylocust beetles
title_full_unstemmed Sexual selection and the evolution of sex-role reversal in honeylocust beetles
title_sort sexual selection and the evolution of sex-role reversal in honeylocust beetles
publisher Uppsala universitet, Zooekologi
publishDate 2015
url http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-246715
http://nbn-resolving.de/urn:isbn:978-91-554-9209-0
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