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Multiple mating (i.e., polyandry) by queens in social Hymenoptera is expected to weaken social cohesion since it lowers within-colony relatedness, and hence, indirect fitness benefits from kin selection. Yet, there are many species where queens mate multiply. Several hypotheses have been put forward to explain the evolution and maintenance of polyandry. Here,we investigated the ‘sperm limitation' and the ‘diploid male load' hypotheses in the ant Cataglyphis cursor. Genetic analyses of mother-offspring combinations showed that queens mate with up to 8 males, with an effective mating frequency of 3.79. Significant paternity skew (unequal contribution of the fathers) was detected in 1 out of 5 colonies. The amount of sperm stored in the spermatheca was not correlated with the queen mating frequency, and males carry on average enough sperm in their seminal vesicles to fill one queen's spermatheca. Analyses of the nuclear DNA-content of males also revealed that all were haploid. These results suggest that the ‘sperm limitation' and the ‘diploid male load' hypotheses are unlikely to account for the queen mating frequency reported in this ant. In light of our results and the life-history traits of C. cursor, we discuss alternative hypotheses to account for the adaptive significance of multiple mating by queens in this species

In a population of the monogynous, polyandrous ant Cataglyphis cursor, we analysed the spatial genetic structure of queens, colony fathers and workers at a microgeographical scale to infer the extent of sex-biased dispersal and to assess the impact of limited dispersal on the patterns of relatedness within the colony. To this end, four microsatellite markers were scored for the queen and an average of 26 workers from each of 35 mapped colonies. We used pair-wise kinship coefficients between all pairs of genotypes, including the reconstructed colony father genotypes (1) to test and quantify isolation by distance patterns within each sex or caste through the analysis of kinship-distance curves, and (2) to compute the average relatedness between categories of colony members. The kinship-distance curve was much steeper for colony queens than colony fathers, indicating male-biased dispersal. However, colony fathers also displayed a non-random spatial genetic structure, so that even males show some dispersal limitation at the scale of the population, which extends over less than 250 m. The degree of relatedness between the different sexes and castes of colonies was well predicted from the number of mates per queen and the inbreeding of queens, and the impact of limited dispersal was very weak at this scale of observation. We discuss the interest of kinship-distance curves to assess sex-biased dispersal on a local scale and we compare our results with large-scale analyses of genetic structure in Cataglyphis cursor and other monogynous ant species. (c) 2008 The Linnean Society of London., info:eu-repo/semantics/published

La sélection de la parentèle est le concept actuellement le plus fréquemment avancé pour justifier l’évolution et le maintien d'une caste ouvrière stérile chez les Hyménoptères sociaux. La fourmi méditerranéenne Cataglyphis cursor possède plusieurs traits biologiques qui font de cette espèce un modèle particulièrement intéressant pour tester les prédictions de la théorie de la sélection de la parentèle, le plus important d'entre eux étant la capacité des ouvrières, qui ne s'accouplent jamais, à produire une descendance mâle (haploïde) par parthénogenèse arrhénotoque, ou femelle (diploïde) par parthénogenèse thélytoque. Nos analyses génétiques, basées sur des marqueurs microsatellites développés au préalable pour cette espèce, ont révélé que les reines utilisent la reproduction sexuée et asexuée respectivement pour la production de la caste ouvrière et reproductrice. L'analyse du pedigree des reproductrices issues de la reproduction asexuée nous a permis d'identifier le mécanisme cytologique de la parthénogenèse thélytoque et d'estimer la proportion de reines issues de la reproduction des ouvrières au sein de la population. De plus, bien que les reines soient capables de produire une descendance diploïde (femelle) par parthénogenèse thélytoque, elles ont conservé la reproduction sexuée pour la caste ouvrière et s'accouplent avec plusieurs mâles. Ceci indique que la reproduction sexuée a une fonction importante au niveau de la colonie, et nous avons testé certaines des hypothèses avancées pour justifier l'évolution de la polyandrie. Finalement, nous avons étudié l'impact des stratégies de dispersion de cette espèce sur le sex-ratio de la descendance sexuée. Ces résultats confirment l'intérêt que représente l'étude des stratégies reproductrices chez les Hyménoptères sociaux pour tester les prédiction de diverses théories en biologie évolutives et ouvrent également de nouvelles perspectives de recherche, tant chez C. cursor que chez d'autres espèces appartenant au genre Cataglyphis., Kin selection is, to date, the most widely accepted theory to justify the evolution of a sterile worker caste among social Hymenoptera. The Mediterranean ant Cataglyphis cursor represents an interesting biological model for several reasons, the most important of them being the ability for unmated workers to produce haploid (male) offspring, through arrhenotokous parthenogenesis, and diploid (female) offspring, through thelytokous parthenogenesis. Our genetic analyses, based on microsatellite loci developed for this purpose, revealed that queens selectively use sexual and asexual reproduction to produce workers and sexuals, respectively. Pedigree analyses allowed us to identify the cytological mechanism involved in thelytokous parthenogenesis and to estimate the proportion of worker-produced queens in the study population. Although C. cursor queens do not require mating to produce diploid offspring, they have retained sexual reproduction and mate multiply with up to 8 males. This suggests that sexual reproduction has important benefits for colony function, and we tested several hypotheses accounting for the evolution of polyandry. Eventually, we studied the effect of dispersal strategies on sex-ratio of the sexual brood. These results confirm the interest of investigating the reproductive strategies of social Hymenoptera to test the predictions of diverse theories in the field of evolutionary biology, and open new research perspectives in C. cursor and other ants of the Cataglyphis genera., Doctorat en Sciences, info:eu-repo/semantics/nonPublished