Interactions between individuals can range from peaceful cooperation, through mediated contest, to escalated conflict. Understanding such diversity of interactions between individuals requires an understanding of the costs and benefits involved with these behaviours, and the influence of relatedness between interacting individuals. Species in the parasitoid wasp genus Melittobia display social behaviours at both extremes of this spectrum, from the potentially cooperative traits of the ratio of male to female offspring that they produce, and the dispersal of females to new habitats, to the extreme conflict of violent contests between males. In this thesis, I examine a number of aspects of social evolution in Melittobia. First, I consider the pattern of sex allocation – the division of resources between male and female offspring - where local mate competition theory predicts that females will adjust their offspring sex ratio (proportion of males) conditionally, with females laying increasingly female biased sex ratios as the number of other females laying eggs on the same patch increases. In Chapter 2, I show that M. acasta females always lay an extremely female biased sex ratio, and that this may be explained in part by the fact that male Melittobia engage in violent lethal combat in competition for mates. Early emerging males have a competitive advantage and thus there is a limited advantage for later laying females to produce a less female biased sex ratio. However, I also demonstrate that the advantage of early emergence can be reduced when we consider male body size, which is linked to fighting ability, suggesting that the occurrence of this extreme conflict does not fully explain the unusual pattern of sex allocation in Mellitobia. In Chapter 3, I examine whether the level of dispersal varies in response to the extent of local competition for resources, and the relatedness between competitors. I use the species M. australica, which readily produces two distinct female dispersing morphs, to show that the production of dispersing females increases with the competition for resources. I consider the parallels between the evolution of dispersal and of sex ratio. In Chapter 4, I examine male fighting in more detail and explore theory that predicts that when extreme conflict does evolve, the incidence of fighting varies with resource value, number of competitors, and the level of relatedness between males. I show that mating opportunities are sufficiently valuable that male Melittobia will always engage in fighting irrespective of relatedness, that there is no evidence of opponent assessment prior to fighting, and that the intensity of fights increases with the number of competitors. This thesis highlights the importance of considering combinations of social traits and the interactions between them, to understand the evolution of social characters.

Orientadores: Mary Anne Heidi Dolder, Jose Lino Neto / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-10T15:36:52Z (GMT). No. of bitstreams: 1 Brito_PedroValedeAzevedo_M.pdf: 5058045 bytes, checksum: a8e944c3ea7b5a920db9f092ea469fc2 (MD5) Previous issue date: 2008 / Resumo: Hymenoptera é uma das maiores ordens de inseto no mundo e nenhum outro grupo possui tantas espécies benéficas para o homem quanto esse. A morfologia dos espermatozóides tem provado ser capaz de fornecer dados úteis para estudos filogenéticos em diversos grupos de insetos, inclusive os Hymenoptera. Porém, os estudos existentes até o momento descrevendo a morfologia dos espermatozóides nessa ordem ainda não são suficientes para permitir inferências filogenéticas mais abrangentes. Neste trabalho descrevemos a morfologia dos espermatozóides de Melittobia hawaiiensis e M. australica (Chalcidoidea) e de Neochrysis lecointei (Chrysidoidea) resultando em dois manuscritos que estão em fase de submissão. Comparando os dados desse estudo com os disponíveis na literatura observamos que algumas características como a presença de estruturas espiraladas nos espermatozóides, presença de material extracelular associado ao ápice dos espermatozóides e a ordem de desorganização dos microtúbulos do axonema no final do flagelo, parecem fornecer informações possíveis de serem utilizadas na filogenia das superfamílias de Hymenoptera. Outras características, como a morfologia do adjunto do centríolo e dos derivados mitocôndrias, parecem ser capazes de fornecer informações que indicam as relações de parentesco entre táxons inferiores, inclusive gêneros (ou tribos) da mesma família / Abstract: Hymenoptera is one of the largest insect orders in the world and no other group presents so many benefic species for humanity. In spite of these insects¿ importance, there are still many uncertainties about this group¿s phylogeny. Spermatozoa morphology has proved useful in resolving phylogenetic questions in many insects¿ orders, including Hymenoptera, although the available studies describing sperm morphology in this order do not include enough taxa to allow detailed phylogenetic studies. This study describes the sperm morphology of Melittobia hawaiiensis and M. australica (Chalcidoidea) and of Neochrysis lecointei (Chrysidoidea), which resulted in two manuscripts to be submitted for publication. Comparing data obtained in this study with those available in the literature there are some characteristics such as the presence of spiraling structures in spermatozoa, the extracellular material coating spermatozoa apex and the order of disorganization of the axoneme microtubules at the flagellum end that could be used to provide information about the Hymenoptera superfamilies¿ phylogeny. Other characteristics, such as the centriolar adjunct and mitochondrial derivatives¿ morphology, provide information about the relationships among inferior taxons, including those of the same genera, or tribes of the same family / Mestrado / Biologia Celular / Mestre em Biologia Celular e Estrutural