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.

The objective of this study was to clarify the regulation of production and signal transduction of juvenile hormone (JH) in insects by experimentally examining the function and evolution of a putative receptor (USP/RXR) and a neuropeptide inhibitor (FGLamide allatostatin). To examine the role of USP/RXR, the cDNA sequence of the receptor was obtained from the cockroach Diploptera punctata. Transcript levels during developmentally critical periods for JH sensitivity may suggest USP/RXR is JH responsive. Comparative sequence analysis of evolutionary rates in the Mecopterida support current hypotheses which suggest some gain in function along this lineage, although this acquisition may have occurred more gradually than previously assumed. To examine allatostatin evolution within insects, ancestral peptides inferred using maximum likelihood ancestral reconstruction methods were assayed for in vitro inhibition of JH production in two cockroach species. Shifts in peptide potency in some ancestral peptides reconstructed may be related to peptide copy number evolution.

The objective of this study was to clarify the regulation of production and signal transduction of juvenile hormone (JH) in insects by experimentally examining the function and evolution of a putative receptor (USP/RXR) and a neuropeptide inhibitor (FGLamide allatostatin). To examine the role of USP/RXR, the cDNA sequence of the receptor was obtained from the cockroach Diploptera punctata. Transcript levels during developmentally critical periods for JH sensitivity may suggest USP/RXR is JH responsive. Comparative sequence analysis of evolutionary rates in the Mecopterida support current hypotheses which suggest some gain in function along this lineage, although this acquisition may have occurred more gradually than previously assumed. To examine allatostatin evolution within insects, ancestral peptides inferred using maximum likelihood ancestral reconstruction methods were assayed for in vitro inhibition of JH production in two cockroach species. Shifts in peptide potency in some ancestral peptides reconstructed may be related to peptide copy number evolution.

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