<p>Sexual selection has long been accepted as a widespread force of evolution shaping male traits across taxa. In recent years, biologists have begun to investigate the extent to which sexual selection may also shape traits among females. However, current models of sexual selection have largely been developed using assumptions that--while generally met in males--often do not apply to females. Thus, attempts to apply these contemporary models to the study of sexual selection in females reveal weaknesses in the theoretical framework for sexual selection research. One consequence of this for empirical research is that researchers often infer the action of sexual selection upon evidence of male mate choice. Although male mate choice is increasingly common, it is much less likely to exert selection pressure than its female counterpart. I begin by proposing a conceptual framework that explicitly accounts for ...Next, I investigate a female trait that has recently become an iconic example of sexual selection in females; that is the exaggerated estrous swellings of cercopithecine primates. By combining morphological data collected with a non-invasive photographic method and observational behavioral data with longitudinal ecological and demographic data from the ongoing Amboseli Baboon Research Project, I examine the sources of variance in this exaggerated signal of fertility. Finally, I test the hypothesis that male baboons prefer females with larger sexual swellings because those females have higher fitness. I find no evidence to support this hypothesis. Instead, my results suggest that mate choice among male baboons has evolved to detect, not the intrinsic quality of the female as has typically been proposed, but the quality of a reproductive opportunity.</p> / Dissertation

Mate choice among males is relatively understudied, despite recent evidence supporting its ubiquity. Theory predicts male mate choice in response to variation in female quality, and male mating strategies that limit polygyny. However empirical research investigating these connections, particularly under natural conditions, is generally lacking. Using the Western black widow spider, Latrodectus hesperus, I investigated male mate choice, male investment, and the advantage of mating with females that differ in their potential to deliver fitness benefits to males via higher fecundity and/or reduced risk of sperm competition. Males were found to be preferentially attracted to larger, high-diet virgin females over females that were smaller due to a lower diet, or having been previously mated, or both. Through a three-year field study on females I found that males likely benefit from selectivity, as smaller, low-diet females often failed to deposit any egg sacs throughout the breeding season, likely due to their shortened web-site tenure and/or lack of bodily resources. I investigated the costs and benefits to male genital breakage in L. hesperus, a strategy typically assumed to result in male sterility while providing paternity protection. I found that genital mutilation in L. hesperus did not cause sterility and that males were capable of inseminating multiple females, likely because of the comparatively low amount of genital damage and the likelihood of the efficient placement of genital fragments. Evidence from double mating trials supported the efficacy of broken genital fragments as plugs, but first male sperm precedence was often maintained in cases where male genital breakage failed or fragments were positioned incorrectly, which occurred frequently. Together, these laboratory and field experiments contribute to a more complete view of mate choice.

Mate choice among males is relatively understudied, despite recent evidence supporting its ubiquity. Theory predicts male mate choice in response to variation in female quality, and male mating strategies that limit polygyny. However empirical research investigating these connections, particularly under natural conditions, is generally lacking. Using the Western black widow spider, Latrodectus hesperus, I investigated male mate choice, male investment, and the advantage of mating with females that differ in their potential to deliver fitness benefits to males via higher fecundity and/or reduced risk of sperm competition. Males were found to be preferentially attracted to larger, high-diet virgin females over females that were smaller due to a lower diet, or having been previously mated, or both. Through a three-year field study on females I found that males likely benefit from selectivity, as smaller, low-diet females often failed to deposit any egg sacs throughout the breeding season, likely due to their shortened web-site tenure and/or lack of bodily resources. I investigated the costs and benefits to male genital breakage in L. hesperus, a strategy typically assumed to result in male sterility while providing paternity protection. I found that genital mutilation in L. hesperus did not cause sterility and that males were capable of inseminating multiple females, likely because of the comparatively low amount of genital damage and the likelihood of the efficient placement of genital fragments. Evidence from double mating trials supported the efficacy of broken genital fragments as plugs, but first male sperm precedence was often maintained in cases where male genital breakage failed or fragments were positioned incorrectly, which occurred frequently. Together, these laboratory and field experiments contribute to a more complete view of mate choice.

No description available.

No description available.

Abstract Sexual ornaments have developed in a very wide variety of animal taxa to increase fitness by improving mating success. How increased mating rate improves fitness is obvious in the case of most males: each mating provides more offspring. Whether more matings benefit females, whose fecundity is limited by resources and not mates, is unclear. Mate choice is linked to ornamentation, when individuals of one sex choose who to mate with based on the ornamentation in members of the other sex. Ornaments may work as a basis for mate choice due to conveying information about the quality of the mate. Mate choice may then lead to intrasexual competition for mates in the chosen sex as animals try to outcompete their neighbours and attract more mates. My aim in this thesis is to study the purpose and costs of female ornamentation as well as female competition for males. The main questions revolve around understanding what information female ornaments provide about the bearer and how males choose between females. I also examine how females compete against each other and what the costs of being ornamented are for a female. To study these questions I use the common glow-worm (Lampyris noctiluca Linnaeus, Lampyridae), whose females glow at night to attract flying males. According to my results, a female’s glowing provides accurate information about fecundity and males base their choice of mate on the intensity of female glowing. I showed that the perceived strength of an ornament in comparison to others close by is more important than the actual strength of an ornament. In the glow-worm, the perceived strength of an ornament depends on distance to the observer, making the system open to exploitation. A mathematical model I developed suggested that dull females could outcompete brighter ones by choosing optimal locations, and experimentation showed this to be the case. Finally, my results show that glow-worm females lose eggs each day they remain unmated. This suggests that the evolution of female ornamentation may have been driven in part by the need to find a mate as soon as possible after eclosion. Which in turn means that female and male ornamentation may have fundamentally different purposes: for females mating soon may be important, where for males the total number of offspring fertilized is critical. / Tiivistelmä Seksuaalisia ornamentteja on kehittynyt hyvin laajaan kirjoon eläinlajeja parantamaan yksilöiden kelpoisuutta nostamalla niiden parittelutodennäköisyyttä. Koirailla parittelutodennäköisyyden ja kelpoisuuden välinen yhteys on yleensä selvä: jokainen parittelu nostaa jälkeläismäärää. Naarailla yhteys ei ole yhtä selvä, sillä niillä jälkeläismäärä yleensä riippuu resurssien saatavuudesta eikä kumppanien määrästä. Parinvalinta on kiinteästi yhteydessä ornamentaatioon: Yhden sukupuolen yksilöt päättävät kenen kanssa paritella toisen sukupuolen yksilöiden ornamenttien laadun perusteella. Ornamentit toimivat valinnan perusteena välittämällä tietoa parin laadusta. Parinvalinta voi johtaa yksilöiden väliseen kilpailuun kumppaneista valitun sukupuolen sisällä. Tässä väitöskirjassa tarkoituksenani on tutkia naaraiden ornamenttien tarkoitusta ja kustannuksia sekä tutkia miten naaraat voivat kilpailla toisiaan vastaan koiraista. Pääkysymykset liittyvät ornamenttien välittämään informaatioon ja siihen miten koiraat valitsevat kumppaninsa. Lisäksi tarkastelen miten naaraat voivat kilpailla keskenään ja mitä kustannuksia ornamenteista on naaraille. Kysymysten selvittämiseksi käytän tutkimuslajina kiiltomatoa (Lampyris noctiluca Linnaeus, Lampyridae), lajia jonka naaraat loistavat öisin houkutellakseen lentäviä koiraita. Tulosteni mukaan kiiltomatonaaraan loiste välittää tarkkaa informaatiota niiden munamäärästä ja koiraat osaavat valita parinsa tämän perusteella. Osoitin, että ornamentin havaittu vahvuus verrattuna ympärillä oleviin on tärkeämpää kuin ornamentin todellinen vahvuus. Kiiltomadolla havaittu kirkkaus riippuu etäisyydestä havaitsijaan, mikä tekee signallointijärjestelmästä avoimen väärinkäytölle. Laatimani matemaattisen mallin mukaan himmeät naaraat voisivat päihittää kilpailussa kirkkaampia valitsemalla parempia loistamispaikkoja. Käytännön kokeet osoittivat tämän pitävän paikkansa. Viimeinen tulokseni oli, että kiiltomadolla naaras menettää osan munistaan joka päivä jonka se joutuu odottamaan parittelua. Tästä voi päätellä, että naaraan ornamentin evoluutiota on voinut osaltaan ajaa tarve paritella mahdollisimman pian aikuistumisen jälkeen. Naaraiden ja koiraiden ornamenttien syyt voivat olla hyvin erilaiset: naarailla parittelu mahdollisimman pian voi olla tärkeintä, kun koiraalla parittelukumppanien määrä on tärkein.

Male mate choice occurs in species in which males face high mating costs, leading to few opportunities to copulate. Additionally, if male-male competition is strong, male mate choice should be influenced by male fighting ability. Good competitors should choose high quality females because they may be able to fight off contenders, while poor competitors should choose lower quality females. In Nephila clavipes spiders, males have limited sperm supply and fight for access to females. Here, using field experiments and observational data, we tested whether female quality and male size (a proxy of fighting ability) affect the pairing likelihood of males. In our experiments, we found that males did not express mate choice initially, but, after a few hours, chose their mates based on female size and female recent pairing status. Importantly, male mate choice direction and intensity varied with male size, as large males guarded larger females that were not recently paired and small males guarded smaller females that were recently paired. The observational data provided little evidence of assortative pairing regarding body size. With our field experiments, we show that crucial information can be collected by assessing mate choice in multiple moments. Taken together, our findings reveal the importance of considering male traits and the social context in understanding variation in male mate choice, which is often neglected in empirical studies / A escolha de parceiras por machos ocorre em espécies em que machos sofrem altos custos associados ao acasalamento, o que gera poucas oportunidades para copular. Adicionalmente, se a competição entre machos é intensa, a escolha de parceiras por machos deveria ser afetada pela habilidade de luta dos machos. Bons competidores deveriam escolher fêmeas de alta qualidade porque eles seriam capazes de afastar rivais, enquanto maus competidores deveriam escolher fêmeas de má qualidade. Em aranhas da espécie Nephila clavipes, machos possuem um estoque limitado de esperma e lutam pelo acesso a fêmeas. Usando experimentos de campo e dados observacionais, testamos se a qualidade das fêmeas e o tamanho dos machos (variável operacional de habilidade de luta) afetam a probabilidade de pareamento dos machos. Nos nossos experimentos, vimos que machos não expressam escolha de parceiras inicialmente, mas, depois de algumas horas, escolhem parceiras baseado no tamanho e no estado recente de pareamento delas. A direção e intensidade da escolha de parceiras por machos variou com o tamanho dos machos, pois machos grandes guardaram fêmeas maiores que não estavam pareadas recentemente, enquanto machos pequenos guardaram fêmeas menores que estavam pareadas recentemente. Nossos dados observacionais forneceram pouca evidência para pareamento assortativo referente a tamanho corporal. Com nossos experimentos de campo, mostramos que informação crucial pode ser coletada avaliando a escolha de parceiras em diferentes momentos. Em conjunto, nossos resultados revelam a importância de considerar características dos machos e contexto social no entendimento da variação na escolha de parceiras por machos, que é comumente negligenciada em estudos empíricos

<p>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.</p>

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.

The evolution of elaborate male ornaments via sexual selection is well-understood while the selective pressures acting on female ornaments remains unresolved. Female ornaments in species with strong sexual selection on the male homologue of the ornament were originally thought to result from an intersexual genetic correlation. My thesis explores the evolution of ornaments in females due to direct selection by developing theoretical models and examining the biology of a neotropical mosquito (Sabethes cyaneus) with sexually homologous ornaments coinciding with male-male competition. I began by exploring the morphology of the ornaments in both sexes of S. cyaneus. Sexual dimorphism in the size and shape of the ornaments was slight and both male and female ornaments showed classic hallmarks of sexually selected traits. I then tested for direct selection on S. cyaneus male and female ornaments via mutual mate choice. I found evidence of male, but surprisingly not female, preferences for ornaments. I then further considered the evolution of male mate choice in polygynous species. First, I investigated whether male investment in courtship by S. cyaneus may result in a lower operational sex ratio and thereby reduce the costs associated with male mate choice. Male courtship did pose a significant longevity cost to male S. cyaneus. Second, I explored the possibility that a female preference for male courtship effort may contribute to the benefits of male mate choice in a series of population genetic models. The spread of a male preference gene can be driven by female preferences for male courtship when males court preferred females more. Finally, I found that female S. cyaneus are not benefitting from signalling to increase their mating rate as they are monandrous. My thesis therefore challenges standing sexual selection theory and suggests that sexual selection on females may be more widespread than previously thought. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 729