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Anisogami och sexuella konflikter kan vara grunden till flera fall av könslig dimorfism. Intralokus sexuell konflikt uppstår när alleler vid ett genetiskt lokus har en antagonistisk effekt på fitness hos hanar och honor. Helgenomstudier har pekat ut flera sexuellt antagonistiska kandidatgener hos Drosophila melanogaster. En av dem, CG15170, har återskapats med hjälp av genediteringstekniken CRISPR/Cas9. Den här genen är intressant då populationer med en viss allel, A1, inte förlorar balanser kromosomen, förmodligen på grund av negativ fitnesspåverkan från den återskapade allelen A1. I den här studien undersöktes om fertiliteten hos honor och ägg-till-vuxen överlevnaden är negativt påverkad. Detta gjordes genom att antalet lagda ägg och proportionen av lagda ägg som utvecklades till vuxna individer hos honor av D. melanogaster homozygota för A1 eller A2 alleler mättes. Resultatet från de statistiska tester som utfördes visade ingen signifikant skillnad mellan honor med A1 och A2 alleler varken för antalet lagda ägg eller proportionen av ägg som utvecklades till vuxna. Däremot upptäcktes en signifikant skillnad mellan de två allelerna i antalet vuxna honor som överlevde parningen i den första delen av försöket. Denna studie kan inte påvisa att fekunditeten hos honorna och den tidiga överlevnadsgraden hos deras avkommor skulle vara olika för honor med A1 respektive A2 alleler. Det bör i stället vara någon annan del av livscykeln som påverkas av att A1 inte förlorar balanser kromosomen men vilken kan ej fastställas utifrån den här studien. / Anisogamy and sexual conflict may be the basis of several cases of sexual dimorphism. Intralocus sexual conflict occurs when alleles at a genetic locus have an antagonistic effect on the fitness of males and females. Genome wide association studies have pointed out several candidate genes for sexual antagonism in Drosophila melanogaster. One of them, CG15170, has been recreated with the gene editing technique CRISPR/Cas9. This gene is interesting because populations with one particular allele, A1, do not lose the balancer chromosome, probably because of negative effects off the allele on fitness. In this study, the fertility and egg-to-adult survival of eggs laid by females was investigated to see if these traits were adversely affected by the recreated allele A1.  This was done by measuring the number of eggs laid by females of D. melanogaster, homozygous for A1 or A2 alleles, and also by measuring the proportion of eggs that developed to adults. The results of the statistical tests that were performed showed no significant difference between females with A1 and A2 alleles, not for the number of eggs laid nor the proportion of eggs that developed into adults. However, a significant difference was detected between the two alleles in the number of adult females that survived the first courtship and mating part of the experiment. Probably some other part of the life cycle is affected by A1 not losing the balancer chromosome, but which cannot be determined by this study.

En raison des forts coûts en temps et en énergie associés à chaque reproduction, les femelles ne sont généralement pas aussi disponibles que les mâles pour se reproduire. Les mâles entrent donc souvent en compétition pour accéder aux femelles disponibles. Ceci conduit à une forte sélection sexuelle chez les mâles. Un des exemples les plus frappants de compétition entre mâles peut être observé chez certaines espèces de crustacés chez qui les femelles ne sont sexuellement réceptives que pour un temps très limité. Les mâles ont donc évolué une stratégie de gardiennage précopulatoire grâce à laquelle ils monopolisent une femelle plusieurs jours avant qu’elle ne devienne réceptive. Ce comportement mâle est lui-même coûteux en temps et en énergie. En conséquence, il a été suggéré que les mâles devraient devenir sélectifs envers les femelles du fait du fort investissement que chaque reproduction représente pour eux. A l’aide d’un modèle mathématique, nous prédisons que les mâles effectuant de longs gardiennages précopulatoires devraient préférer s’apparier avec les grandes femelles plus fécondes. Toutefois, cette sélectivité devrait rester faible du fait de la forte compétition pour accéder aux femelles libres. Nous suggérons plutôt que les mâles devraient chercher à s’apparier avec des femelles de bonne qualité après s’être initialement apparié avec une femelle. Quand les mâles en couple rencontrent une femelle libre de meilleure qualité que leur propre femelle, ils devraient quitter leur femelle pour s’accoupler avec la nouvelle femelle. Contrairement à cette prédiction, nos expériences ont montré que les mâles en couple d’un crustacé amphipode Gammarus pulex ne changeaient pas systématiquement de femelle quand nous leurs proposions une femelle de meilleure qualité que leur propre femelle. Ils décidaient de changer de partenaire uniquement quand leur femelle était de mauvaise qualité, indépendamment de la qualité de la nouvelle femelle libre. D’autres expériences sont nécessaires pour comprendre le caractère adaptatif de ce comportement de changement de partenaire, seulement basé sur une partie de l’information disponible. Ces deux études soulignent la difficulté d’inférer des patrons de reproduction uniquement à partir des préférences individuelles. Dans la première étude, les mâles étaient contraints par la compétition pour accéder aux femelles libres. Dans la seconde, le processus de prise de décision des mâles conduisait à un comportement de choix apparemment sous-optimal. Ces contraintes n’ont que rarement été prises en compte malgré leur grande importance lorsqu’il s’agit de comprendre les causes comportementales d’un patron de reproduction très répandus chez les crustacés à gardiennage précopulatoire : l’homogamie pour la taille. Il a principalement été suggéré que ce patron de reproduction était issu d’une préférence mâle pour les grandes femelles associée à un avantage des grands mâles pour accéder aux femelles. Cette hypothèse n’a malgré tout reçu que peu de support empirique. A l’aide d’un modèle par simulation individu centrée, nous avons donc testé l’hypothèse selon laquelle une préférence mâle pour la distance à la mue des femelles serait à l’origine de l’homogamie pour la taille chez les crustacés à gardiennage précopulatoire. Quand les mâles préfèrent s’apparier avec des femelles qui sont strictement plus proches de la mue qu’eux, les couples formaient un patron d’homogamie pour la taille. Puisque plusieurs préférences différentes peuvent conduire à un même patron de reproduction, ce résultat souligne l’importance de considérer le processus complet de mise en couple pour étudier le lien entre les préférences individuelles et les patrons de reproduction. Les stratégies de femelles peuvent aussi jouer un rôle important dans les processus de mise en couple. Contrairement aux mâles, les femelles ont été décrites comme préférant les gardiennages courts du fait des coûts associés à la mise en couple. / Because of strong costs associated with each mating event, females are usually not as available for reproduction as males at any given time. Males are therefore in competition with each other for access to receptive females, hence leading to strong sexual selection. One textbook case of such a mating system occurs in moulting crustaceans where females can only be fertilized during a short period following their moult. This has favoured the evolution male strategies to monopolize females before their period of receptivity. Such a precopulatory mate guarding is widespread among many taxa and represents one of the most striking example of males’ competitive traits favoured by sexual selection. However, recent investigations have suggested that because males’ sexually selected traits often involve opportunity or mortality costs, males should become choosy towards females. Using a theoretical approach, we showed that males performing long lasting mate guarding should choose larger, more fecund females. However, under sequential encounter of potential mates, competition for female access decreases male choosiness before entering in precopula. We rather suggest that males should become choosy after initial pairing with a female. When encountering an unpaired female of better quality than their current female, paired males should switch partners. Contrary to our expectations, even under simultaneous encounters of two females, males did not seem to assess their relative quality. Instead they decided to change partner when their own female was of low absolute quality. This led to several cases where males forewent the possibility of increasing their fitness. Further investigations are needed to understand the adaptive significance of using only a subset of information in decision making. These two cases highlight the difficulty of inferring mating patterns from mating preferences only. In the first case, male preference was constrained by competition for access to females while in the second one, sampling processes led to apparent suboptimal mate choices. These potential constraints on decision making have rarely been acknowledge in precopulatory mate guarding crustaceans in spite of their major importance when inferring the causes of a well-known pairing pattern occurring in these species: size-assortative pairing. Size assortment among pairs has mainly been considered to come from a male directional preference for larger females associated with a large male advantage in getting access to preferred females. However, this hypothesis has received contrasted empirical support and little is known about the underlying pairing process causing size-assortative pairing. We investigated theoretically the possibility that a state-dependent male mating preference could account for size-assortative pairing. When males chose females which were exclusively closer to moult than them, assortative pairing by size arose under strong male-male competition. Because several preferences can account for a given pattern, this result emphasises the importance of considering the whole pairing process when studying the link between preferences and mate choice. Female strategies may also be of great importance during the pairing process. Contrary to males, females have been suggested to prefer short precopulatory mate guarding due to costs associated with pairing. Such a sexual conflict over guarding duration may have major effects on co-evolutionary dynamics between males and females traits. Proving its occurrence is yet challenging because empirical studies often lack a full economical survey of costs and benefits for females associated with male traits. Females benefits associated with long lasting precopulatory mate guarding have particularly been overlooked in previous studies. Here, we proposed several potential benefits for females and discuss their influence on sexual conflict over guarding duration.

Em espécies que exibem cuidado paternal exclusivo, a qualidade esperada do comportamento paternal pode influenciar as decisões de acasalamento das fêmeas e determinar o sucesso de acasalamento dos machos. Nesta tese, investigamos a inter-relação entre o cuidado paternal e a seleção sexual utilizando o opilião Quindina limbata como organismo modelo. Os machos nesta espécie constroem ninhos na forma de taça que são visitados pelas fêmeas na busca de um sítio de oviposição. No primeiro capítulo, nós experimentalmente avaliamos a eficiência do atendimento aos ovos provido pelos machos e testamos se os ninhos desatendidos são adotamos por fêmeas e/ou por machos não relacionados com os ovos. As conclusões mais importantes deste capítulo são: (1) a proteção do macho é crucial para a sobrevivência dos ovos porque ninhos desatendidos são prontamente atacados por predadores; (2) a compensação do cuidado parental por fêmeas é rara, provavelmente porque elas estão associadas aos machos e não aos ninhos; (3) os machos adotam ovos não relacionados com eles e protegem eles tão eficientemente quanto os machos originais, provavelmente porque o cuidado dos ovos é um comportamento selecionada sexualmente. No segundo capítulo, nós testamos a existência de duas táticas alternativas de acasalamento nas fêmeas: residentes, na qual as fêmeas permanecem perto de um ninho, repelem fêmeas conespecíficas e copulam preferencialmente com um único macho dono de ninho, e visitantes, na qual as fêmeas não permanecem espacialmente associadas a ninhos, não repelem conespecíficas e copulam com vários machos donos de ninhos. Também investigamos se a monopolização de ninhos por fêmeas afeta o sucesso reprodutivo dos machos. As conclusões mais importantes deste capítulo são: (1) o comportamento das fêmeas parece ser uma tática reversível, na qual as fêmeas podem mudar de residentes a visitantes durante sua vida, provavelmente em resposta à condição corporal, e (2) a monogamia social imposta pelas fêmeas residentes pode afetar negativamente o grau da promiscuidade dos machos, mas não sua taça de acasalamento. Em conclusão, nós provemos evidência de que a preferência das fêmeas por machos que provem cuidado pode ter favorecido a manutenção do cuidado paternal. Além disso, demonstramos que a monopolização dos melhores machos ou ninhos pode ter favorecido a evolução das táticas alternativas de acasalamento nas fêmeas / In species exhibiting exclusive male care, the expected quality of paternal behavior can influence female mating decisions and thus determine male mating success. In this thesis, we investigated the interplay between paternal care and sexual selection using the harvestman Quindina limbata as model organism. Males of this species build cup-like mud nests that are visited by females in search of an oviposition site. In the first chapter, we experimentally evaluated the efficiency of egg-attendance provided by males and tested if unattended nests are adopted by females and/or unrelated males. The most important conclusions of this chapter are: (1) male protection is crucial for egg survival because unattended nests are promptly attacked by predators; (2) flexible compensation of parental care by females is rare, probably because they are associated to males and not to the nests; (3) males adopt unrelated eggs and protect them as efficiently as original owner males, probably because egg-attendance is a sexually-selected behavior. In the second chapter, we tested the existence of two reproductive tactics in females: resident, in which females remain close to a nest, repel conspecific females, and mate preferentially with a single nest-owner male, and wanderer, in which females are not spatially associated with nests, do not repel conspecific females, and mate with different nest-owner males. We also investigated whether nest monopolization by females may affect males\' reproductive success. The most important conclusions of this chapter are: (1) females\' behavior seems to be a reversible tactic, in which females can switch from resident to wanderer during their lifetime, probably in response to body condition, and (2) the social monogamy imposed by resident females may negatively affect the degree of male promiscuity, but not male\'s mating rate. In conclusion, we provide evidence that female preference for parental individuals may have favored the evolution and maintenance of paternal care. Moreover, we show that the monopolization of the best males or the best nests may have favored the evolution of alternative reproductive tactics in females

Sexual conflicts arise when there is a difference in how females and males of a species or population achieve their maximum reproductive fitness. In intralocus sexual conflicts, alleles at a given locus are exposed to conflicting, or antagonistic, selection pressures. Based on a Genome-wide association study on sexually antagonistic genes in Drosophila melanogaster (fruit flies), the aim of this study was to investigate whether the candidate gene CG3598 exhibits sexually antagonistic effects on fitness between the 2 identified alleles of the gene. The study was performed on females from a Canton-S population of D. melanogaster who, by genetic manipulation through CRISPR Cas9, carried one of the 2 alleles of the CG3598. 6 excision lines of females had allele 1 and 5 excision lines had allele 2. The females were mated with "wild type" males from a Canton-S population in mediums prepared with about 6 mg of live dry yeast, after which the females were moved to separate mediums to lay their eggs. After 12 days, the adult offspring were counted and statistical calculations were performed on the average number of offspring per female for each line and allele. An Independent sample t-test showed that the females’ average fecundity did not differ between alleles (p = 0.059) and a Nested ANOVA analysis indicated that the average fecundity for each line within each allele differed (p = 0.023). Due to the fact that similar studies have found the same result, it may be necessary to investigate and possibly change the experimental design of the method to enable competition between females with different genetic conditions in order to observe a difference in fertility based on the females' ability to compete. / Sexuella konflikter uppstår när det finns en skillnad i hur honor och hanar i en art eller population uppnår sin maximala reproduktiva fitness. Vid intralocus sexuella konflikter utsätts alleler vid ett givet locus för motstridiga, eller antagonistiska, selektionstryck. Baserat på en Genome-wide association study om sexuellt antagonistiska gener hos Drosophila melanogaster (bananflugor) syftade denna studie till att undersöka huruvida genkandidaten CG3598 uppvisar sexuellt antagonistiska effekter på fitness mellan de 2 identifierade allelerna av genen. Undersökningen utfördes på honor från en CantonS-population av D. melanogaster som genom genmodifiering av CRISPR Cas9 bar en av de olika alleler av genen CG3598. 6 linjer av honor bar allel 1 och 5 linjer bar allel 2. Honorna parades med ”wild type”-hanar från en CantonS-population i rör preparerade med ca 6 mg levande torrjäst, varpå honorna förflyttades till separata rör för att lägga sina ägg. Efter 12 dagar räknades de vuxna avkommorna och statistiska beräkningar utfördes på det genomsnittliga antalet avkommor per hona för respektive linje och allel. Ett oberoende t-test visade att honornas genomsnittliga fekunditet inte skiljde sig mellan alleler (p=0,059) och en Nested ANOVA-analys indikerade att genomsnittlig fekunditet för varje linje inom respektive allel skiljde sig (p=0,023). Då även liknande studier funnit samma resultat kan det vara nödvändig att studera och eventuellt förändra den experimentella designen av metoden för att möjliggöra konkurrens mellan honor med olika genetiska förutsättningar för att kunna observera en skillnad i fekunditet baserat på honornas förmåga att konkurrera.

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Postcopulatory sexual selection—sperm competition and cryptic female choice—has become a major area of research over the past 40 years. Within this field there are many outstanding questions at every level of analysis, from proximate to ultimate. The fitness consequences for both sexes in the period after copulation and before fertilization are considerable, but are obscured within the female reproductive tract. Our understanding of postcopulatory mechanisms is especially sparse in taxa other than birds and insects. Nearly nothing is known in reptiles except that multiple paternity is common and widespread, and often results from long-term sperm storage across breeding seasons. We present some of the very first data on the determinants of fertilization success in the context of sperm competition in reptiles, a group that accounts for 30% of terrestrial vertebrates. In the first chapter, "Asymmetric gametic isolation between two populations of red-sided garter snakes", we discuss the use of between-population crosses to reveal gametic isolation. The effect of population density and operational sex ratios on mating systems and the speciation process has fueled theoretical debate. We attempted to address these issues using two populations of red-sided garter snakes (Thamnophis sirtalis parietalis) from Manitoba, Canada. Our study populations differ markedly in their density mating aggregations, with a 10-fold difference between them. Using microsatellite markers for paternity analysis of litters produced from within and between population crosses. We found that the population with highest aggregation density, and presumably with the highest level of sexual conflict (i.e., when the evolutionary interests of the sexes differ) over mating, was also the population that exhibited homotypic sperm precedence. The less dense population showed a distinct postcopulatory male-size advantage. We also demonstrated that sperm stored within the female over hibernation can father 20-30% of offspring in a litter. In the second chapter, "Sperm competition and mate-order effects in red-sided garter snakes", we test whether females use mate-order effects to ensure that a larger (fitter) male will sire her offspring. Does that second male should have precedence in sperm competition? We tested for second-male precedence using singly-mated females that mated with a second male. Average proportion of paternity was shared equally among the first (P₁, i.e., proportion of offspring from a litter fathered by the first male to mate) and second males (P₂) to mate, and stored sperm (P[subscript ss]). This may be a case where last male precedence breaks down with more than two males. All females were spring virgins (they had not mated that spring, but may have stored sperm from fall matings); thus sperm stored presumably from fall matings is important in this system. As the interval between matings increased P₁ increased at the expense of P[subscript ss]. As the second male to mate's copulation duration increased, P₁ also increased at the expense of P₂. This last result may indicate female influence over sperm transfer during coerced matings. Copulatory plugs (CPs) are found in many taxa, but the functional significance is debated. Male garter snakes produce a gelatinous copulatory plug during mating that occludes the opening of the female reproductive tract for approximately two days. In chapter three, "Not just a chastity belt: the role of mating plugs in red-sided garter snakes revisited", we experimentally tested the role of the CPs. In snakes, sperm are produced in the testes and delivered through the ductus deferens, and the copulatory plug is thought to be produced by the sexual segment of the kidney and conveyed through the ureter. We manipulated the delivery of the two fluids separately by ligating the ducts. We confirmed that the CP is not formed in ureter-ligated males and that sperm leaks out immediately after copulation. The CP is analogous to a spermatophore. The protein matrix contains most of the sperm which are liberated as the plug dissolves within the female's vaginal pouch. One of the fundamental principles in sperm competition is that increased sperm numbers increase the odds of winning in competitions for fertilization success and males will adjust their ejaculate relative to competition and the quality of his mate. In chapter four, "Sperm depleted males and the unfortunate females who mate with them", we detect significant among-male variation in the number of sperm ejaculated, and that male mate-order reduces sperm numbers. Male sperm numbers drop significantly from one mating to the next, and this has implications for sperm competiveness, as Thamnophis sirtalis exhibits a disassociated reproductive tactic, in that sperm stores are produced outside the breeding season, and thus cannot be replenished after mating. Interestingly, however, the on average the mobility of the sperm increased for a male's second mating. Therefore, increased sperm quality may compensate for reduced numbers in a competitive context. Further, females increase their remating rate when mating with males that are unable to deliver sperm. In chapter five, "Sexual conflict during mating in red-sided garter snakes as evidenced by genital manipulation", we revisited the CP in the context of sexual conflict. Sex-differences in optimal copulation duration can be a source of conflict, as increased copulation duration may be advantageous for males as it delays female remating. Males of many species actively guard females to prevent them from remating, and in some cases males produce copulatory plugs to prevent remating. If precopulatory choice is limited at the time of her first mating, conflict may be especially onerous to a female. The size of the plug is influenced by the copulation duration. We experimentally tested the contribution of male and female control over copulation duration. We ablated the largest basal spine on the male's hemipene and found a reduction in copulation duration and an increase in the variation of plug mass. Further, we anesthetized the female's cloaca and found copulation duration increased, which suggests that males benefit from increased copulation duration while females actively try to reduce copulation duration. Therefore, sexual conflict is manifest in divergent copulation duration optima for males and females. / Graduation date: 2013