Sociality is widespread across the animal kingdom and explanations for its incidence and persistence are numerous. Whilst various drivers of sociality have been identified and tested, controversies remain and we are still far from a complete understanding of the mechanisms underlying social structure. Here I use a combination of field observations on a free-living population of feral horses Equus caballus and laboratory behavioural experiments on the Pacific beetle roach Diploptera punctata to investigate the drivers of sociality in these species. I explore four key aspects of sociality: the influences of kinship on sociality and social development, the strength and persistence of social bonds, the relationship between inbreeding avoidance and dispersal and the potential influence of individuals on social structure. Whilst kinship is a major driver of social structure in most mammalian species, I present evidence in Chapter Three that horse society is not structured by levels of kinship; however, in Chapter Five, I show that kinship levels to potential mates are significant in female dispersal choices in this species. In Chapter Eight, I provide evidence for significant effects of kinship to companions upon social and physical development in D. punctata, indicating a clear potential benefit of kin-based associations. The stability of social bonds can have substantial effects upon social structure. In Chapter Three, I show that the bonds between female horses show significant stability and are formed independently to kinship levels, a rare result in a non-primate species. I also provide evidence consistent with the hypothesis that these bonds are driven by male harassment. Similarly, in D. punctata, I find in Chapter Eight that female clustering occurs within resting aggregations and that the most likely explanation is the avoidance of male harassment. I therefore propose that this driver of female sociality may be a highly prevalent force structuring animal societies. Inbreeding depression has been demonstrated in a variety of species and contexts. Here I show in Chapter Five that in horses, female dispersal is likely to be influenced by kinship levels with potential mates. In Chapter Four, I then show that more heterozygous males have a higher reproductive success, most likely due to their ability to utilise a larger home range. Finally, local population structure can be highly influenced by individual association choices and behaviour. In Chapter Two, I show that in horses, mothers may allow their sons to postpone dispersal by the maintenance of stronger mother-son bonds, permitting an extended period of social learning. In Chapter Seven, I demonstrate that consistent inter-individual variation in personality traits exists in D. punctata which is stable across life stages, despite age effects on the strength of boldness. This is a source of variation which may be extremely important for decision-making social groups. My main conclusion from this work is that male harassment is often a key driver of sociality which may frequently be overlooked. I also demonstrate that the effects of kinship are far-ranging but not omnipresent. This thesis therefore makes a major contribution to our understanding of the mechanisms underlying animal sociality and presents clear potential avenues for future research.

This study examined population genetics of greater sage-grouse (Centrocercus urophasianus) in Strawberry Valley, Utah located in the north-central part of the state. The Strawberry Valley population of sage-grouse experienced a severe population decline with estimates of abundance in 1998 less than 5% (~150 individuals) of similar estimates from the 1930s (>3,000 individuals). Given the population decline and reduced genetic diversity, recovery team partners translocated sage-grouse from four different populations into Strawberry Valley over 6 years (2003-2008). Translocations have been used as a strategy to increase both population size and genetic diversity in wildlife populations. We assessed whether genetic diversity increased following the translocation of sage-grouse into Strawberry Valley by looking at both nuclear and mitochondrial DNA indices. We observed an overall increase of 16 microsatellite alleles across the 15 loci studied (x̅ =1.04 alleles per locus increase, SE ± 0.25). Haplotype diversity increased from 4 to 5. Levels of genetic diversity increased for both nuclear and mitochondrial DNA (16% and 25% increases for allelic richness and haplotype diversity, respectively). These results show that translocations of greater sage grouse into a wild population can be an effective tool to increase not only population size but also genetic diversity.Second, we studied fitness-related traits and related them to genetic diversity indices in a population of greater sage-grouse in Strawberry Valley, Utah from 2005 to 2013. We captured 93 sage-grouse in Strawberry Valley and fitted them with a radio collar and drew and preserved blood. We monitored sage-grouse weekly, throughout each year. From blood, we extracted and amplified DNA with 15 microsatellite loci. We determined genetic diversity as multilocus heterozygosity and mean d2. To determine if there was a relationship between genetic diversity and survival, we used known-fate models in Program MARK. We also determined if there was a relationship between genetic diversity measures and nest initiation, nest success, clutch size, and number of eggs hatched using generalized linear models where reproductive measures were modeled as a function of genetic diversity. We found no significant relationship between mean d2 and microsatellite heterozygosity with measures of survival or reproductive fitness. Overall, these results suggest that the often-reported strong heterozygosity-fitness correlations detected in small, inbred populations do not reflect a general phenomenon of increasing individual survival and reproductive fitness with increasing heterozygosity.

La gorgone rouge, Paramuricea clavata (Cnidaire, Octocoralliaire), est une espèce sessile, longévive à faible croissance dont les populations présentent une lente dynamique. Cette espèce est caractérisée par une phase larvaire pélagique qui représente l’unique phase de dispersion potentielle au cours du cycle de vie de cette espèce. P. clavata est une espèce clé des assemblages à coralligène de Méditerranée, qui subit les effets combinés des activités de plongée sous-marine et du changement climatique. Dans ce contexte, il était donc fondamental d’approfondir les connaissances sur les traits d’histoire de vie, la biologie et l’écologie de cette espèce. L’objectif de ce travail était d’étudier, à l’aide d’une approche génétique, les facteurs biologiques et écologiques clés qui devraient être importants pour la réponse de l’espèce aux changements environnementaux. Parmi ces facteurs, la dispersion larvaire joue un rôle fondamental dans la dynamique et la connectivité des populations marines. Dans le contexte actuel des fortes pressions anthropiques, la compréhension des degrés de connectivité entre les populations est primordiale pour évaluer le devenir des populations, face au changement climatique, et pour mettre en place des plans de conservation et des réseaux d’aires marines protégées. / The red gorgonian, Paramuricea clavata (Cnidaria, Octocorallia), is a sessile, long-lived and slow growing species which displays slow population dynamics. This species is characterized by a pelagic larval phase that represents the sole potential phase of dispersal during the life cycle of this species. P. clavata is a key species of coralligenous assemblages of the Mediterranean Sea which undergoes the combined effects of diving activities and climate change. In this context, extending the knowledge about life history traits, biology and ecology of the red gorgonian was of fundamental importance. Using a genetic approach, the goal of this work was to study some key biological and ecological factors which should be important for the response of this species to environmental changes. Among these factors, larval dispersal plays a major role in driving marine population dynamics and connectivity. In the current context of strong anthropic pressures, understanding the level of population connectivity is primordial to evaluate population outcome, facing climate change, and to develop conservation plans as well as to design marine reservenetworks.