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Sexual selection is a widespread evolutionary force that acts on variation between individuals in reproduction, driving the evolution of traits that increase fertilisation success. Although generally well-studied, there are gaps in our understanding of how sexual selection (1) impacts population-level fitness, and (2) shapes trait divergence at the level of the gamete. Here, I investigate these questions using experimentally evolved populations of the promiscuous flour beetle, Tribolium castaneum, which vary only in contrasting strengths of sexual selection across 58+ generations. For population fitness, sexual selection is theorised to act either positively or negatively, depending on its alignment with natural selection, and/or the impact of sexual conflict. I found no evidence for either consistently positive or negative effects of sexual selection history on adult resistance to environmental stresses or intrinsic ageing. However, significant and consistent benefits of strong sexual selection histories were recorded within the ability of individuals to cope with poor nutrition. Furthermore, a history of strong sexual selection improved a population’s ability to invade novel, intra-specific competitor populations across multiple generations, demonstrating superior biotic fitness across life history traits. Overall, these results provide evidence for population fitness benefits of sexual selection. At the gamete level, sperm number is known to be a vital predictor of sperm competition success, however, the influence of sexual selection on the huge diversity in sperm morphology remains unclear. I found that strong sexual selection led to the evolution of greater sperm competitiveness in adult males, and this was associated with increasing sperm length divergence, but no effect on length variance. Finally, a study of sex-specific ageing in this promiscuous species revealed that stark sexual dimorphism in reproductive senescence was associated with sexual dimorphism in intrinsic lifespan, supporting ageing theories and suggesting significant differences in the cost of early reproduction for males and females.

Two geographical strains of Callosobruchus maculatus beetles with contrasting life histories were compared. Female Callosobruchus maculatus beetles were manipulated to experience four different mating treatments. Multiple mating in a Brazil strain increased fecundity but decreased longevity of females. Multiple mating by Brazil-strain parents also reduced the longevity of their singly mated offspring. In contrast, multiple mating in a South India strain had no effect on longevity or fecundity of female parents or their singly mated offspring. South-India-strain females mated more frequently than Brazil-strain females when mating opportunities were limited but not when females had constant access to males. Mating frequency decreased in Brazil-strain females when presented the virgin males. In contrast, South-India-strain females mated more frequently on the second and third days when presented with virgin South-India-strain males. Brazil-strain males mated for longer and males transferred proportionally larger spermatophores than South-India-strain males. Spermatophore mass was positively correlated with male emergence mass for the South-India-strain males only. These differences are interpreted in relation to the contrasting life-history strategies of the two strains and trade-offs between the fitness components of longevity and fecundity.

The prioniodontids were the first to develop a functionally differentiated apparatus. The apparatuses of selected prioniodontid taxa are reconstructed by direct comparisons between elements from disjunct collections and those preserved in natural assemblages of Promissum pulchrum. These comparisons and evidence of internal morphology have enabled the recognition of homologous elements. Examination of prioniodontid hard tissues has provided a clearer understanding of conodont hard tissues. Polished sections have provided evidence of intergradation between white matter and hyaline tissues confirming their synchronous deposition. Also surface ornamentation is shown to be directly related to internal structure. Apparatus reconstructions and studies of internal and external wear patterns also reveal new evidence for element function. Elements occluded in a way broadly comparable to those of the ozarkodinid elements (Donoghue and Purnell, 1999a), though interlocking occlusion only occurs in association with a well formed blade. Where a blade is not developed, elements simply worked against each other, wearing down the oral surfaces. Phragmodus inflexus represents the second prioniodontid apparatus preserved as a natural assemblage and its architecture, presented here, differs markedly from that of Promissum. This has important implications for prioniodontid apparatus architecture, as the elements of Phragmodus are comparable to those typical of many prioniodontids not included with the balognathids. This may suggest that apparatuses of most prioniodontids had an ozarkodinid-like apparatus and that Promissum possesses a more derived plan. This new evidence is important for understanding phylogenetic relationships between prioniodontids. Realistic cladistic studies should be based on clearly understood homologous characters and it is hoped that in the future, cladistic analyses will draw from detailed data, such as those presented here.

The concept of automated species identification is relatively recent and advances are being driven by technological advances and the taxonomic impediment. This thesis describes investigations into the automated identification of ladybird species from colour images provided by the public, with an eventual aim of implementing an online identification system. Such images pose particularly difficult problems with regards to image processing as the insects have a highly domed shape and not all relevant features (e.g. spots) are visible or are fore-shortened. A total of 7 species of ladybird have been selected for this work; 6 native species to the UK and 3 colour forms of the Harlequin ladybird (Harmonia axyridis), the latter because of its pest status. Work on image processing utilised 6 geometrical features obtained using greyscale operations, and 6 colour features which were obtained using CIELAB colour space representation. Overall classifier results show that inter-species identification is a success; the system is able to, among all, correctly identify Calvia 14-guttata from Halyzia 16-guttata to 100% accuracy and Exochomus 4-pustulatus from H. axyridis f. spectabilis to 96.3% accuracy using Multilayer Perceptron and J48 decision trees. Intra-species identification of H. axyridis shows that H. axyridis f. spectabilis can be identified correctly up to 72.5% against H. axyridis f. conspicua, and 98.8% correct against H. axyridis f. succinea. System integration tests show that through the addition of user interaction, the identification between Harlequins and non-Harlequins can be improved from 18.8% to 75% accuracy.

Investment in immunity is costly: one way in which hosts can ameliorate these costs is through immune priming, whereby hosts develop increased protection to future infection following previous exposure to a parasite or immune elicitor. Priming offers hosts a more efficient way of managing immune insult by allowing for a stronger and faster response to an immune insult. As well as investing in physiological immune defences, hosts can also leverage behavioural responses to reduce the costs of infection. Group-living in insects offers several benefits, such as predator avoidance. However, it can be costly in terms of increasing the risks of exposure to parasites. Group facilitation of disease resistance through a variety of processes collectively known as 'social immunity' is well established in the eusocial insects. Many gregarious insects share several features of their ecology with eusocial species, and should thus be predisposed to many of the same risks of infection, and the same evolved processes that mitigate these risks. A form of immune priming known 'social immunisation' has recently been described in eusocial insects, whereby immunologically naïve individuals exhibit enhanced immunity against infection after being housed with infected nestmates. Whether similar mechanisms exist in gregarious but non-social insects is unknown, and it is this premise that forms the conceptual basis of this thesis. I investigated whether a non-social but gregarious insect, the mealworm beetle (Tenebrio molitor), altered its immune investment following cohabitation with an immunestimulated conspecific. I examined the potential role of both physiological and behavioural defences in offering prophylactic protection against perceived pathogenic threat. I also investigated the potential mechanisms of such an form of immunisation by examining immune responses induced by cohabitation with conspecifics challenged by a live (and transmissible) bacterial infection and those challenged by either heat-killed bacteria or an artificial antigen (both non-transmissible). Finally, I examined the role of host behaviour in affecting immunisation, quantifying behavioural changes in immune-stimulated hosts (referred to as 'sickness behaviours') to try and identify visual or behavioural cues which may be utilised by naïve hosts to stimulate prophylactic defences, There was no robust evidence for a parsimonious process of gregarious immunisation. However, there were differences between the sexes in their immune responses to infection threat, as well as in their induction of sickness behaviours following infection. Whilst there was little evidence for an upregulation of immunity in naïve females, females appeared to exhibit enhanced tolerance of infection following cohabitation with a 'sick' conspecific, as they suffered no decrease in longevity despite the presence of relatively high parasite loads. Males showed the opposite pattern to that predicted by gregarious immunisation, decreasing their investment in physiological defence following exposure to 'sick' conspecifics. Despite finding no clear evidence for enhanced resistance through a straightforward process of gregarious immunisation, these data suggest that naïve T. mollitor may be able detect social cues of infection produced by parasitised conspecifics. I propose that the immune responses displayed by both males and females constitute tolerance strategies which help hosts to minimise the costs of parasitism. Due to intrinsic differences in the life-history trajectories of the sexes, females are predicted to invest in immunological tolerance mechanisms aimed at self-preservation in order to preserve their capacity for future reproduction, whereas males are predicted to terminally invest in reproduction in order to maximise their fitness.

No description available.

No description available.

No description available.

No description available.