Sexual selection is a prevalent evolutionary force that prominently led to the evolution of elaborate and conspicuous traits. However, it remains an ongoing scientific debate if sexual selection has a net negative or positive effect on the general viability of a population (from here on ‘population fitness’). Sexual selection could reduce the fitness of a population, when sexual conflict leads to, for example, one sex harming the other during mating. By contrast, sexual selection could increase population fitness, if it increases selection against deleterious alleles in the gene pool. This could be the case if sexual selection acts on traits that capture the genetic quality of an individual. Indeed, recent meta-analytic evidence suggests that sexual selection typically increases population fitness. Therefore, the strength of sexual selection could prove important for the fitness of wild populations facing environmental stress. Importantly, the strength of sexual selection can differ fundamentally between the sexes and also among populations or species. One reason that might trigger this variation is the interdependence of evolutionary and ecological processes, also known as eco-evolutionary dynamics. Therefore, studying eco-evolutionary dynamics could help us to understand the vast variation in sexual selection and to predict the effect of sexual selection on population fitness. I studied different pathways of eco-evolutionary dynamics in diverse environments using experimental and comparative approaches: First, I investigated the effect of diet quality on the strength of selection in females and males in a model insect. I show that low diet quality increased the potential for selection in males and females, but surprisingly the effect of diet was particularly pronounced in females. This suggests that deteriorating diet quality might be predominantly stressful for females and could disproportionally increase selection on females compared to males. Overall, this study provides an example of how an ecological factor can influence the strength of selection. Secondly, I performed an experimental study to test the effect of a key demographic factor on sexual selection. To this end, I manipulated the density of populations of the red flour beetle by changing population size as well as habitat size. By quantifying mating behaviour and fitness, I demonstrated that an increase in density can have an impact on the potential for sexual selection. Especially in females, higher densities caused an increase in sexual selection, whereas in males, higher densities mainly increased the benefitted of additional matings. These effects were most profound when varying density through the number of individuals, whereas habitat size barely affected sexual selection. Collectively, this suggests that density dependent sexual selection mediates eco-evolutionary dynamics, which can be particularly important for the fitness of declining populations. Thirdly, I took a comparative approach to study how the strength of selection in general might alter the demography of populations, specifically their carrying capacity (i.e. the limit for population growth). Since population growth is typically limited by females, strong selection on males can affect the carrying capacity of a population. If selection is typically stronger in males compared to females, females could benefit from selection against deleterious alleles in males without the reduction in population growth imposed by strong selection on females. I compiled data on the genetic variance in fitness for females and males as a measure for the strength of selection. I found that selection is typically stronger in males compared to females across the animal kingdom. Sexual selection theory suggests that such a sex-difference in the strength of selection could be caused by stronger sexual selection on males. Indeed, the sex difference in selection strength was only significant in polygamous and not in socially monogamous species, with the latter presumably experiencing weaker sexual selection. In conclusion, these data suggest that in polygamous species selection is typically stronger on males compared to females and the sex-specific strength of selection could have an effect on the carrying capacity of populations. After exploring the relevance of sexual selection in the previous chapters, I fourthly, tested the robustness of a widely used and easily obtainable proxy for the strength of sexual selection across species: sexual size dimorphism. Theory predicts that sexual selection on males promotes the evolution of larger males relative to females. Indeed, my comparative study shows that the degree of sexual size dimorphism was significantly correlated with the strength of sexual selection, estimated by a diverse range of proxies for the strength of sexual selection from primary studies. Importantly, pre-copulatory sexual selection correlated positively with an increasing male-bias in sexual size dimorphism, while post-copulatory sexual selection was non-significantly negatively associated with the degree of male-bias in sexual size dimorphism. Overall, these data suggest that sexual size dimorphism can be a useful, albeit rough, proxy for the strength of pre-copulatory sexual selection across species. In the final chapter, I synthesise the results of my studies in the light of their implications for eco-evolutionary dynamics. While there is evidence that sexual selection could typically improve population fitness, the data I present suggest that the ecology of a population, here specifically diet quality and population density, could have a crucial impact on the strength of (sexual) selection. Hence, unravelling the eco-evolutionary dynamics of (sexual) selection could prove important for our understanding of their effect on population fitness. Importantly, selection seems to be typically stronger in males compared to females, at least in species with prevalent sexual selection on males. Overall, further exploration of the eco-evolutionary dynamics of sexual selection and their effects on population fitness promise to be exciting and profitable future endeavours.

This study explores the relationship between wing size, coloration, and reproductivesuccess in Drosophila melanogaster, fruit flies. Sexual selection, a key aspect ofevolutionary biology, often involves visual signaling as a means of displaying geneticinformation. The study aims to identify the morphological traits targeted by sexualselection, specifically examining the hypotheses that both wing size and coloration(thin-film interference patterns) influences reproductive success, and that these traitsare correlated. Data was collected from standardized images of 229 fruit flies thatwere used in a competitive mating assay, and the analysis included color analyses inFiji (ImageJ) to obtain red, green, and blue (RGB) values, as well as sizemeasurements in both vertical and horizontal size dimensions for one wing from eachfly. Statistical analyses, including correlation analysis and multiple regression inSPSS, were conducted to examine the relationships between morphological aspects,color, and mating success in the competitive mating assay. Results indicate asignificant relationship between horizontal wing length and male reproductivefitness, suggesting that larger wings may confer advantages in mate choice andreproductive success for males. Phenotypic selection analysis indicated thathorizontal wing length is under significant directional selection independent of wingcoloration, which was not subject to significant selection. The correlation analysisrevealed a weak but significant correlation between wing size and average coloration.Sexual dimorphism in wing dimensions was observed, with females exhibiting largerwings than males. The study suggests that coloration may be influenced by wing size,raising questions about the causal relationship between wing size, coloration, andreproductive success. Importantly, this study suggests that wing size may be a moreimportant target of selection than wing color, suggesting that past findings of sexualselection on color without consideration of wing size or shape may be premature. / Den här studien undersöker förhållandet mellan vingstorlek, färg och reproduktivframgång hos Drosophila melanogaster, bananflugor. Sexuell selektion, en viktigaspekt inom evolutionsbiologi, involverar ofta visuell signalering som ett sätt att visaupp genetisk information. Studien syftar till att identifiera de morfologiskaegenskaper som är mål för sexuell selektion, och framför allt granska hypotesen attbåde vingstolek, färg (“thin-film interference patterns” som uppstår när ljus faller påen tunn film och ger färgglada reflektioner) influerar reproduktiv framgång, och attdessa egenskaper korrelerar med varandra. Data samlades in från standardiseradebilder av 229 bananflugor som använts i ett konkurrensbaserat parningsexperiment,och min analys bestod av färganalys i Fiji (ImageJ) för att få röda, gröna och blå (RGB) värden, såväl som storleksanalys av både vertikal och horisontell längd hosvarje fluga. Statistisk analys, däribland korrelationsanalys och multipelregressionsanalys i SPSS, utfördes för att granska relationen mellan morfologiskaegenskaper, färg och den reproduktiva framgången i parningsexperimentet.Resultaten indikerar att det finns ett signifikant förhållande mellan horisontellvingstorlek och hanarnas reproduktiva framgång, vilket tyder på att större vingar kan medföra fördelar vid partnerval och reproduktiv framgång för dem. Fenotypisktselektionsanalys pekade mot att horisontell vingstorlek är under ett signifikant riktatselektionstryck oberoende av färgen på dem, som i sig inte var föremål för någotsignifikant selektionstryck. Korrelationsanalys visade en svag men signifikantkorrelation mellan vingstorlek och genomsnittlig färgning. Sexuell dimorphismobserverades i vingstorlek, där honorna visade sig ha större vingar än hanarna.Studien föreslår att färgen på vingarna är beroende av vingstorleken, vilket väckerfrågor kring de kausala sambanden mellan vingstorlek, färg och reproduktivframgång. Framför allt föreslår denna studie att vingstorlek att vingstorleken kanvara kan ett vara betydligt större mål för sexuell selektion än vad färgen är, vilket i sintur antyder att de tidigare resultaten som pekat mot att sexuell selektion agerar påvingarnas färg har konstaterats i ett för tidigt skede, då vingstoleken inte varit en aspekt man har haft med sig i beräkningarna.

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[pt] Para Charles Darwin, a criatividade artística dos humanos encontra paralelos com manifestações estéticas de outros animais, como o canto e a habilidade de algumas aves para construir ninhos decorados. Por que diferentes espécies teriam desenvolvido essas capacidades psicológicas? Para Darwin, a resposta é a seleção sexual. A presente tese é composta por estudos que têm por objetivo testar predições esperadas diante da possibilidade da inteligência e da criatividade em humanos terem evoluído ao menos parcialmente por seleção sexual. O primeiro capítulo apresenta uma revisão integrando evidências numa rede nomológica para verificar se a literatura empírica em conjunto sustenta a evolução da criatividade por algum processo ligado à seleção sexual. O segundo capítulo apresenta um estudo qualitativo cujo objetivo foi verificar se inteligência e criatividade emergiriam como categorias de critérios de atratividade diante de respostas espontâneas dos participantes sobre as características de um parceiro amoroso ideal. O terceiro testa as relações da sapiossexualidade com outras variáveis psicológicas, enquanto o quarto estudo testa as relações da atração por comportamentos criativos com outras variáveis psicológicas. Finalmente, o quinto estudo trata-se de um experimento cujo objetivo foi testar se inteligência e criatividade eram atraentes em si mesmos ou por causa de suas consequências sociais benéficas. Os resultados apresentados nesta tese indicam que a inteligência e a criatividade podem ter evoluído parcialmente por seleção sexual, embora o processo específico (bons genes e etc.) possa não estar claro. Além disso, os estudos empíricos mostraram que mulheres são mais sapiossexuais e preferem mais parceiros criativos do que homens. Além disso, a atração por inteligência e criatividade parece ligada à estratégia reprodutiva de curto prazo. / [en] For Charles Darwin, the artistic creativity of humans finds parallels with aesthetic manifestations of other animals, such as the song and the ability of some birds to build decorated nests. Why would different species have developed these psychological capabilities? For Darwin, the answer is sexual selection. This thesis is composed of studies that aim to test expected predictions given the possibility that intelligence and creativity in humans have evolved at least partially by sexual selection. The first chapter presents a review integrating evidence in a nomological network to verify if the empirical literature as a whole supports the evolution of creativity by some process linked to sexual selection. The second chapter presents a qualitative study whose objective was to verify if intelligence and creativity would emerge as categories of attractiveness criteria in the face of spontaneous responses from participants about the characteristics of an ideal love partner. The third tests the relationships of sapiosexuality with other psychological variables, while the fourth study tests the relationships of attraction to creative behaviors with other psychological variables. Finally, the fifth study is an experiment whose aim was to test whether intelligence and creativity were attractive in themselves or because of their beneficial social consequences. The results presented in this thesis indicate that intelligence and creativity may have evolved partially by sexual selection, although the specific process (good genes, etc.) may not be clear. Furthermore, empirical studies have shown that women are more sapiosexual and prefer creative partners more than men. Furthermore, the attraction to intelligence and creativity seems to be linked to short-term reproductive strategy.

<p>Alternative reproductive tactics (ARTs) have been described across taxa numerous times, and are especially common in fishes. The advent of molecular techniques has enhanced our understanding of such mating systems, yet these techniques have only been applied to relatively few species. Furthermore, ecological variation has long since been recognized as an important factor influencing mating patterns and sexual selection, yet it is often ignored. In my thesis, I conducted field studies to investigate the reproductive ecology of a species with well characterized ARTs, the plainfin midshipman (<em>Porichthys notatus</em>), and to explore how these mating patterns varied across time and space. This species is characterized by two male tactics: guarders and sneakers. I show that both tactics are successful at gaining fertilization. Indeed, I found evidence for several behavioural adaptations by the guarder male tactic to gain fitness, including guarding, nest takeovers, and plastic cuckoldry behaviours. I also documented the lowest paternity for guarder males for a species with obligate male parental care. Paternity increased over the course of the breeding season, which was likely a result of a higher occurrence of nest takeovers early in the season. In a cross-population analysis of plainfin midshipman, I found significant differences in nest availability and density between two genetically distinct populations, but this did not translate into significant differences in mating patterns. Taken together, my thesis helps elucidate the reproductive ecology of a classic species with ARTs, and has important implications for our understanding of ecological influences on mating patterns and sexual selection.</p> / Doctor of Philosophy (PhD)

Sexual selection has been investigated in many different systems but information is lacking in joint-nesting species. Both sexual dimorphism and possible signals of quality were explored in this study for a joint-nesting plural breeder, the smooth-billed ani (Crotophaga ani). Sexual dimorphism can be examined for a species in an attempt to reveal particular traits that might be under sexual selection and the strength of sexual selection on them. In mate choice decisions, sexually selected traits may be used by the choosy individual to assess the quality of potential mates. These honest traits need to reveal the condition and genetic quality of the individual accurately. For example, it has been proposed that plumage colour reveals condition, and more specifically parasite resistance in birds. This study explores sexual size dimorphism and dichromatism in smooth-billed anis, as well as the ability of their feather colour to reveal body condition (measured as residuals from a regression of mass versus body size), body size, and parasite numbers. Additionally, because anis are group living birds, this study investigated whether group size had an effect on parasite numbers. Anis from a population in southwestern Puerto Rico were measured for size, their feathers were collected and analyzed using a spectrometer, and ectoparasites were collected by dustruffling. For all size traits measured, males were significantly larger than females. Males also had more exaggerated bill depths (relative to body size) than females. There were no differences between the sexes for all colour morphometries, except tail saturation; females had more saturated tails than males. While no decisive conclusions can be drawn as to why the dimorphic traits are different between males and females, sexual selection may have played a role. The relationship between log10 average lice numbers per group and group size was positive, but not significant. In male smooth-billed anis, plumage colour was not related to lice or mite numbers, or body size and body condition. Plumage colour was also not related to body condition and size in females. Additionally, ectoparasites did not have an effect on male body condition. Plumage may not only be an inaccurate signal of parasite resistance or body size and body condition in the smooth-billed ani, but ectoparasites may not even have a negative effect on their host. The inability to find significant results may have been affected by other factors, such as feather wear and the age of individuals. These results warrant a more detailed look into the social behaviour of the group-living smooth-billed ani. / Thesis / Master of Science (MSc)

Particularly lacking in the current body of sexual selection literature are studies based on reptile species and intrasexually selected mating systems. Because the life history traits and ecology of reptiles are dramatically different from other animal taxa, current models of sexual selection are insufficient for predicting how sexual selection should influence the behavior and mating systems of lizards. Similarly, intersexually selected mating systems (i.e., based on female choice) are inappropriate predictive models for examining species with intrasexually selected mating systems (i.e., based on consexual contests). I investigated three aspects of Anolis carolinensis behavior and mating system (communication signals, male mate preference, and reproductive energetics) to contribute to a theoretical model for sexual selection based on a lizard with an intrasexually selected, polygynous mating system. In my first study, I quantified the structure and use of signals exchanged by both sexes, compared signal structure and use during heterosexual interactions to that of other social contexts (e.g., male-alone, male-male, female-female), then related signal structure and use to the species mating system. During heterosexual interactions, both sexes performed three kinds of stereotypic headbob displays with equal precision that were essentially identical to those previously documented for other social contexts. Thus, there is no courtship-specific headbob display for A. carolinensis. However, male and female signal use was extremely dimorphic. For the purpose of indicating sexual identity, the sexually dimorphic patterns of signal use were excessively redundant, yet equivocal. Although the male pattern of signal use reliably conveys sexual identity, the female pattern of signal use conveys ambiguous sexual identity. Based on circumstantial evidence from other studies, I propose the hypothesis that the female pattern of signal use may permit female-sized, nonterritorial males to mimic female signals. Small males may be selected to use female mimicry to gain access to the territories of larger males and mating opportunities with resident females, while females may be indirectly selected to use a signaling pattern that provides them with an alternative mating option. From field and laboratory data on A. carolinensis signal behavior during other social contexts and the species' female-defense mating system, I evaluate proposed functions for heterosexual signaling from a perspective of intrasexual selection. In my second study, I tested the prediction that males should include a preference for mating with novel females (PNF) as part of their mating strategy. This prediction was supported by both laboratory and field manipulations. Compared to their encounters with resident females, males during laboratory encounters with novel females significantly increased their display rate, volley frequency, volley length, and significantly decreased the distance and number of movements traveled away from the female. My laboratory data also suggest that males discriminated novel females from resident females independently of female behavioral or chemical cues. Similarly, compared to their interactions with resident females, free-ranging males responded to introduced novel females by significantly increasing the proportion of time spent in female-directed activities and the proportion of displays directed toward novel females, and significantly decreasing the proportion of time spent in territorial activities and the proportion of displays used in territorial activities. Data from both experiments indicate that males appear to distinguish among individual females, and use this ability to increase reproductive success by identifying and preferentially pursuing novel females over previously inseminated resident females. I suggest that males are able to cognitively identify individual resident females, and use this ability to control mating decisions within their territories. In my third study, I examined the energy expenditure of males and females during breeding and postbreeding seasons. I used laboratory respirometry to determine resting metabolic rates, and the doubly-labeled water technique to determine field metabolic rates in free-ranging lizards. Resting metabolic rates were significantly influenced by body mass and season, but not sex. Field metabolic rates were significantly influenced by body mass, but not sex or season. I attributed the ~40% seasonal increase in resting metabolic rates to a seasonal increase in feeding rates and the effect of specific dynamic action. Resting and field metabolic rates were used to calculate energy budgets for each sex during breeding and postbreeding seasons, and to calculate the energy expended by each sex for reproduction. Despite having 40% smaller body mass, females expended 46% more energy for reproduction than males, and a similar amount of total maintenance energy as males. The total maintenance energy of males was similar during both seasons, however that of females decreased 44% from breeding to postbreeding season. I found both seasonal and sexual differences in the amount of energy lizards allocated to resting and activity. Anolis carolinensis had field metabolic rates that were similar to tropical and temperate species of lizards, and higher than lizards from arid/semiarid environments. Anolis carolinensis also expended more energy on eggs, and more total energy during the breeding season, than lizards from arid/semiarid habitats. / Ph. D.

Procreation is often viewed as a joint undertaking where both parties depend on, and thus care about, the reproductive success of the other. This is however not always the case. Sexual antagonism occurs when males and females have different strategies for maximizing their fitness, leading to a “battle between the sexes”. Intralocus sexual conflict, IASC, involves sexual antagonism between different alleles at a specific locus, alleles that have opposite effects between the sexes. One potentially sexually antagonistic gene is Ugt36E1, a gene involved in the catalyzation of a conjugation reaction between different sugars from the donor uridine diphosphate (UDP) to many small, fat-soluble, often toxic exogenous or endogenous molecules. This makes them water soluble, after which they can be transported to various organs for elimination. The gene is thus very important for detoxification and for maintaining the homeostasis of the body’s cells. The purpose of the study is to investigate whether changes in the gene Ugt36E1 affect the fitness of female fruit flies in the form of an increased/decreased number of offspring. To accomplish this, female flies that had been modified using CRISPR/Cas9 to obtain two alternative alleles of the Ugt36E1 gene were collected and allowed to mate with wild-type males. The number of eggs and live offspring of the females were thereafter counted and analyzed. The study could not find a significant difference in the number of offspring between the alleles, which does not line up with previous studies. The gene is hypothesized to be important for both detoxification and homeostasis within the individual regardless of gender, and changes to this gene could therefore be thought to be harmful to both males and females, something that does not seem to agree with this study. Females also laid fewer eggs than expected across both groups. This could be the result of natural variation, but it could also indicate that something during the experiment affected them in a way that reduced their fecundity. Because of the results, and because the study was focused solely on the female side of the conflict, additional testing to further investigate the gene’s effect on the fitness of both genders is recommended. / Fortplantning ses ofta som ett gemensamt åtagande där båda parter är beroende av, och därför bryr sig om, den andras reproduktiva framgång. Detta är dock inte alltid fallet. Sexuell antagonism uppstår när hanar och honor har olika strategier för att maximera sin kondition, vilket leder till en "kamp mellan könen". Intralocus sexual conflict, IASC, innebär sexuell antagonism mellan olika alleler på ett specifikt lokus, alleler som har motsatta effekter mellan könen. En potentiellt sexuellt antagonistisk gen är Ugt36E1, en gen involverad i katalyseringen av en konjugationsreaktion mellan olika sockerarter från donatorn uridindifosfat (UDP) till många små, fettlösliga, ofta toxiska exogena eller endogena molekyler. Detta gör dem vattenlösliga, varefter de kan transporteras till olika organ för eliminering. Genen är alltså mycket viktig för avgiftning och för att upprätthålla homeostasen i kroppens celler. Syftet med studien är att undersöka om förändringar i genen Ugt36E1 påverkar konditionen hos fruktflugor i form av ett ökat/minskat antal avkommor. För att åstadkomma detta samlades bananflugehonor som hade modifierats med CRISPR/Cas9 för att erhålla två alternativa alleler av Ugt36E1-genen och fick para sig med hanar av vildtyp. Antalet ägg och levande avkommor från honorna räknades därefter och analyserades. Studien kunde inte hitta någon signifikant skillnad i antalet avkommor mellan allelerna, vilket inte stämmer överens med tidigare studier. Genen antas vara viktig för både avgiftning och homeostas inom individen oavsett kön, och förändringar av denna gen kan därför tänkas vara skadliga för både hanar och honor, något som inte verkar stämma överens med denna studie. Honor lade också färre ägg än förväntat i båda grupperna. Detta kan vara resultatet av naturlig variation, men det kan också tyda på att något under experimentet påverkade dem på ett sätt som minskade deras fruktsamhet. På grund av resultaten, och eftersom studien enbart fokuserade på den kvinnliga sidan av konflikten, rekommenderas ytterligare tester för att ytterligare undersöka genens effekt på konditionen hos båda könen.