<p>Small populations are facing a particular risk of extinction due to a lack of appropriate genetic diversity and associated negative effects, factors dealt with in the discipline of conservation genetics. Many orchid species exhibit characteristics that make them a perfect study object in the scope of conservation genetics. The aim with this thesis was to investigate genetic structure at different levels in two orchid species <i>Gymnadenia conopsea</i>, geographically widespread, although diminishing and <i>G. odoratissima</i> with a long history of being rare. Microsatellite markers, developed in and used in studies of <i>G. conopsea</i> were also used in the study of <i>G. odoratissima</i>.</p><p>Populations of <i>G. conopsea</i> expressed high levels of genetic variation and a certain amount of gene flow, although investigated mating pattern in a small population indicated non-random mating among individuals, with the majority of pollen exchange between near neighbours, and noticeable levels of geitonogamous pollinations. Further a pronounced year to year variation in flowering frequency among individuals was found. </p><p>It was also discovered that flowering time variants (early and late) within the species <i>G. conopsea</i> were highly differentiated and seem to have had a more ancient historical separation than the separation between the two different species, <i>G. conopsea</i> and <i>G. odoratissima. </i></p><p>Levels of genetic variation in the rare congener, <i>G. odoratissima</i> differed between island and mainland populations where the more numerous island populations expressed larger levels of genetic variation and were less differentiated compared to the few remaining and genetically depauperated mainland populations.</p><p>Uppsala University Library, Box 510, 75120, Uppsala, Sweden </p>

Small populations are facing a particular risk of extinction due to a lack of appropriate genetic diversity and associated negative effects, factors dealt with in the discipline of conservation genetics. Many orchid species exhibit characteristics that make them a perfect study object in the scope of conservation genetics. The aim with this thesis was to investigate genetic structure at different levels in two orchid species Gymnadenia conopsea, geographically widespread, although diminishing and G. odoratissima with a long history of being rare. Microsatellite markers, developed in and used in studies of G. conopsea were also used in the study of G. odoratissima. Populations of G. conopsea expressed high levels of genetic variation and a certain amount of gene flow, although investigated mating pattern in a small population indicated non-random mating among individuals, with the majority of pollen exchange between near neighbours, and noticeable levels of geitonogamous pollinations. Further a pronounced year to year variation in flowering frequency among individuals was found. It was also discovered that flowering time variants (early and late) within the species G. conopsea were highly differentiated and seem to have had a more ancient historical separation than the separation between the two different species, G. conopsea and G. odoratissima. Levels of genetic variation in the rare congener, G. odoratissima differed between island and mainland populations where the more numerous island populations expressed larger levels of genetic variation and were less differentiated compared to the few remaining and genetically depauperated mainland populations. Uppsala University Library, Box 510, 75120, Uppsala, Sweden

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.