Dissertations / Theses on the topic 'Eusocialité'

Le mode de vie des animaux repose sur un ensemble de comportements qui nécessitent une détection et un traitement fiables de l'information sensorielle par les circuits neuronaux. Le système olfactif, qui perçoit l'environnement chimique, a été modelé par diverses pressions de sélections, entraînant une diversification de son organisation. L'ordre des Hyménoptères se révèle pertinent pour aborder la question de l'adaptation des traits sensoriels. Il englobe en effet plusieurs transitions écologiques ayant entraîné une grande diversité de modes de vie, de la phytophagie à la prédation, en passant par diverses formes de parasitisme ainsi que plusieurs transitions vers l'eusocialité. L'eusocialité est une forme avancée d'organisation sociale, où des individus aident d'autres individus apparentés à se reproduire au détriment de leur propre reproduction. Du fait de la vulnérabilité des comportements altruistes au parasitisme, les Hyménoptères eusociaux distinguent les membres de leur colonie des étrangers grâce à des mélanges de composés odorants, les hydrocarbures cuticulaires (CHCs). Les fourmis et les frelons détectent les CHCs via le sous-système des sensilles basiconiques, nommé le BaS, qui divise le premier centre olfactif (le lobe antennaire, LA). Les fourmis et les frelons étant indépendamment eusociaux et phylogénétiquement distants, nous avons cherché à retracer l'histoire évolutive du LA chez les Hyménoptères afin de déterminer si l'eusocialité ou d'autres facteurs écologiques participent à façonner le système olfactif. Nous avons d'abord étudié de ce trait en comparant la neuroanatomie de quatorze espèces recouvrant la phylogénie des Formicidae. Malgré des variations significatives dans le volume et le nombre de glomérules, nous avons observé une conservation de l'organisation du LA, avec un investissement relatif généralement constant dans BaS. Nos analyses ont révélé que des traits comportementaux ou sociaux ne semblent pas influencer le LA, mais que la complexité du mélange de CHC semble être un facteur potentiellement déterminant. Nous avons ensuite examiné les Vespidae, qui incluent deux émergences indépendantes de l'eusocialité avec des espèces solitaires apparentées, permettant ainsi de tester si le BaS constitue une adaptation favorisée par l'eusocialité ou un attribut préexistant, hérité d'ancêtres solitaires. Nous avons trouvé que les ancêtres solitaires des espèces sociales étaient déjà pourvus d'un BaS comprenant un grand nombre de glomérules. La distribution des glomérules entre le BaS et le reste du LA varie entre les différentes sous-familles eusociales, tandis que les espèces solitaires possèdent un nombre de glomérules similaire, voire supérieur, dans les deux régions du LA. Ces résultats suggèrent que l'eusocialité ne joue pas un rôle prédominant dans l'évolution du LA. Nous avons ensuite exploré les origines évolutives de ce sous-système en menant une étude comparative du LA chez les Hyménoptères. Nos résultats suggèrent que le BaS est généralement conservé chez la plupart des parasitoïdes, mais qu'il est réduit, voire absent chez les abeilles, ce qui laisse supposer que l'organisation globale du LA chez les Hyménoptères est influencée par le parasitisme et les comportements alimentaires. La variation du nombre d'unités fonctionnelles dans le LA semble être indépendante de l'eusocialité et semble aussi refléter des différences dans les régimes alimentaires. Cette étude comble une lacune importante dans notre connaissance du système olfactif des hyménoptères et apporte un éclairage nouveau sur son évolution
Animal lifestyles depend on a set of adaptive behaviours that rely on the accurate detection and processing of sensory information within neural circuits. The olfactory system, which perceives the chemical environment, has evolved under diverse selective pressure, diversifying its neural circuits. Hymenoptera represents an ideal order for studying the principles of sensory system adaptation, owing to their diverse lifestyles. From plant feeding to predation, and from diverse forms of parasitism to the repeated evolution of cooperative social structures, Hymenoptera provide numerous opportunities for comparative studies of neural trait evolution. Particularly, eusociality is an advanced form of social organisation, where individuals refrain from their own reproduction for the benefit of reproducing relatives. Due to the vulnerability of altruistic behaviour to exploitation, the evolution of eusociality is hypothesised to be intimately linked with the development of efficient recognition and communication systems. In insects, this recognition involves the perception of odorous compounds known as cuticular hydrocarbons (CHCs), facilitating the discrimination of social partners. In ants and hornets, the detection of CHCs is known to involve the basiconic sensilla subsystem (BaS), which represents a morphological division within the first olfactory processing centre of the brain, the antennal lobe (AL). Given that eusociality evolved independently from solitary ancestors in these two taxa, our investigation focuses on the origin and diversification of this sensory specialisation across solitary and social Hymenoptera, aiming to uncover the influence of social and ecological factors on the olfactory system. We first conducted a comparative study of neural traits within the olfactory system of fourteen ant species distributed across the Formicidae phylogeny. We found that the general organisation of the ant olfactory system is conserved across species, despite remarkable differences in neuropil volume and number of glomeruli. Although we did not identify clear behavioural, ecological, or social traits potentially shaping AL elaboration, our results identified the species-specific complexity of CHC blend composition as a potential driver of neural investment in the BaS subsystem. Then, concentrating on the Vespidae, in which eusociality emerged twice independently, we asked if the BaS subsystem could represent an adaptation driven by the social lifestyle or if it was a pre-existing attribute inherited from solitary ancestors. Based on extensive neuroanatomical data, we show that the solitary ancestors of social species were already equipped with an elaborated BaS subsystem. Moreover, we found divergent AL investment between the different eusocial subfamilies, while solitary species exhibited similar or even greater investment in AL glomeruli. These findings suggest that eusociality has probably not been a major driver of AL evolution. Finally, we investigated the evolutionary origins and elaboration of the BaS subsystem by carrying out a broad comparative neuroanatomical study of the AL across the Hymenoptera. Our data suggest that the BaS subsystem is conserved across most parasitoid and aculeate clades. However, it is remarkably reduced or even lost in bees, indicating that the overall AL organisation in Hymenoptera evolved under strong selection pressure associated with dietary behaviour, rather than the level of social organisation. These studies fill important gaps in our understanding of sensory evolution in Hymenoptera and provide valuable insights into the specific roles of ecological and social factors in driving sensory adaptation

In order to improve our knowledge of the mechanisms of ageing in animals, the main objective of the thesis was to understand the modulation of such mechanisms by the individual social role, within different social organisations. This objective thus addresses two main questions: i) describing the covariation of the degree of social complexity with ageing patterns; ii) highlighting the underlying cellular and molecular processes. Thanks to complementary and diversified studies (behavioural observations, dosage of the oxidative balance, qPCR measurement of telomere length, proteomics, metabolomics), the present thesis showed that sociality plays a role on ageing at many levels. In the zebra finch, social stress caused by aggression of the conspecifics induces oxidative stress and reduces telomere length in adults. In the sociable weaver, the social environment is of crucial importance during pre- and post-hatch development on the medium term survival of the chicks. Finally, in ants, we were able to show a positive relationship between the degree of sociality and maximum potential life span: this link was caste specific, being only significant for the most social queens. This is inline with a recent review by Lucas and Keller (2020) which concluded that the benefits of sociality are most sensitive for high levels of sociality and particularly in reproductive individuals. With regard to the molecular mechanisms of ageing,we were able to establish a causal chain between social stress, oxidative response and telomere erosion in zebra finches.The role of telomeres as a predictor of offspring survival has been confirmed (over at least 5 years) in the sociable weaver,a cooperative breeder bird. However, this link was not true in queen ants where the longest lived were those with the shortest telomeres. The co-evolution of anti-cancer mechanisms and longevity seems to be conserved since similar strategies are found in taxa as diverse as ants and rodents. On the other hand, and contrary to previous studies conducted on ants, we found that oxidative stress might be a marker of individual ageing. We suggest that the proxies of oxidative stress used so far in ants have been misleading or at least incomplete. Thus, understanding the physiological ageing particularities of ants and other social insects might require finding new relevant and specific markers. Finally, the sirtuins and mTOR signalling pathways, key precursors of which we have detected in ants, are molecular crossroads capable of activating or inhibiting cellular metabolism depending on the cell energy state. According to the studies carried out to date, these signalling pathways are among the first to be able to slow down the effects of ageing and extend life expectancy.However, specific studies need to be carried out to understand their fine regulation and thus assess the universality of these mechanisms in animal ageing. Based on our findings, we propose three points to be further addressed to better understand the mechanisms of ageing in social insects: i) the setup of experiments testing the effectiveness of energy trade-offs involving immunity or digestion metabolism; ii) measuring the telomerase activity among castes of various species in order to explore the telomere and telomere independent roles played by this enzyme in ageing; iii) the need to think about individual longitudinal follow-up and to study wild populations, after the first necessary stages in laboratory.
Doctorat en Sciences
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Many animals live in societies of varying degrees of organization. Some individuals in these societies seem to sacrifice their own fitness to increase the fitness of some others. Understanding the forces that mould the evolution of such altruistic behaviour has become a dominant theme in modern evolutionary biology. Primitively eusocial polistine wasps provide excellent model systems to study the evolution of altruism as they show high degrees of plasticity in their behaviour. Different individuals in the same population pursue different social strategies such as nesting alpne or nesting in groups. When wasps nest in groups, usually only one individual becomes the egg layer, while die rest assume the role of sterile workers. Why do the workers not become solitary foundresses and rear their own offspring instead of working to rear the brood of another individual? Here I have used the tropical primitively eusocial wasp Ropalidia marginata to explore some factors that might potentially favour the worker strategy over the solitary founding strategy. Workers in multiple foundress nests may benefit by rearing brood more closely related to them than their own offspring would be. However, from previous work on this species it is known that relatedness between sisters is rather low and that workers therefore rear quite distantly related brood. Therefore, I have concentrated on factors other than genetic relatedness that might potentially favour the worker strategy. A total of 145 naturally initiated nests with different numbers of foundresses was monitored over a period of 16 months, and their productivities were compared. Although the total colony productivity increased, the per capita productivity did not increase with increasing foundress numbers. Colonies with larger foundress numbers did not produce significantly heavier progeny and did not produce them significantly faster than colonies with fewer individuals. The conspecific usurpers preferred to usurp single foundress colonies more often than multiple foundress colonies. Therefore, protection from conspecific usurpers might be an advantage of multiple foundress associations. About 10% of the multiple foundress nests experienced queen turnovers. This provides a finite chance to reproduce and gain some individual fitness for workers, at some future point of time. Wasps may not be similar in their reproductive abilities and those who are less fertile might be joining others who are more fertile. Testing such a hypothesis would require that individuals who have chosen to be subordinate cofoundresses in multiple foundress associations are forced to nest alone. During this study a total of 77 nests was monitored. Cofoundresses forced to nest alone had significantly lower productivity than natural solitary foundresses and also queens of multiple foundress nests who were forced to nest alone. This suggested that wasps are not similar either in their reproductive ability or brood rearing ability or both. To ascertain which of the factors was responsible for lower productivity in cofoundresses, productivity of wasps isolated into laboratory cages was compared. There was no significant difference in the productivity of isolated cofoundresses and isolated queens. This suggests that wasps are not subfertile per se but probably differ in their foraging and brood rearing abilities. The certainty with which resources are brought into the nest and therefore, the certainty with which the mean per capita productivity is attained, provides an automatic benefit of group living according to the central limit theorem. This prediction was also tested. The coefficient of variation of mean per capita productivity decreased significantly with increasing foundress numbers. Behavioural observations on another 36 colonies, with different number of adults, showed that the coefficient of variation of food brought to the nest and the rate at which larvae were fed, decreased significantly with increasing number of adults. A computer simulation was used to find out the effect of group size on the variance in feed larva. Assuming that larvae cannot be starved for too long and cannot utilize more than a certain amount of food at a time, the fitness of larvae was found to increase with an increase in the number of adults attending the nest. Previous work on R. marginata has been largely confined to postemergence colonies. An attempt was made to look at and compare social organization in preemergence colonies with that of postemergence colonies. It was found that the egg layer was not the most dominant animal in the well-established preemergence colonies. There were no detectable differences in the social organization of the preemergence colonies (of this study) with that of postemergence colonies of the earlier studies. Perhaps my conclusions drawn from studying preemergence colonies are therefore applicable more widely to the species. It can be concluded that the apparent increased fitness of the worker strategy over solitary foundress strategy does not come from any increase in per capita productivity, but comes instead from (i) the greater predictability with which the mean per capita productivity is attained in larger colonies, (ii) the lower probabilities of usurpation of larger colonies, (iii) queen turnovers that provide opportunities for workers in multiple foundress colonies to gain some direct individual fitness and (iv) the lower brood rearing abilities of workers in multiple foundress nests that make the worker strategy the best of a bad job.

Many animals live in societies of varying degrees of organization. Some individuals in these societies seem to sacrifice their own fitness to increase the fitness of some others. Understanding the forces that mould the evolution of such altruistic behaviour has become a dominant theme in modern evolutionary biology. Primitively eusocial polistine wasps provide excellent model systems to study the evolution of altruism as they show high degrees of plasticity in their behaviour. Different individuals in the same population pursue different social strategies such as nesting alpne or nesting in groups. When wasps nest in groups, usually only one individual becomes the egg layer, while die rest assume the role of sterile workers. Why do the workers not become solitary foundresses and rear their own offspring instead of working to rear the brood of another individual? Here I have used the tropical primitively eusocial wasp Ropalidia marginata to explore some factors that might potentially favour the worker strategy over the solitary founding strategy. Workers in multiple foundress nests may benefit by rearing brood more closely related to them than their own offspring would be. However, from previous work on this species it is known that relatedness between sisters is rather low and that workers therefore rear quite distantly related brood. Therefore, I have concentrated on factors other than genetic relatedness that might potentially favour the worker strategy. A total of 145 naturally initiated nests with different numbers of foundresses was monitored over a period of 16 months, and their productivities were compared. Although the total colony productivity increased, the per capita productivity did not increase with increasing foundress numbers. Colonies with larger foundress numbers did not produce significantly heavier progeny and did not produce them significantly faster than colonies with fewer individuals. The conspecific usurpers preferred to usurp single foundress colonies more often than multiple foundress colonies. Therefore, protection from conspecific usurpers might be an advantage of multiple foundress associations. About 10% of the multiple foundress nests experienced queen turnovers. This provides a finite chance to reproduce and gain some individual fitness for workers, at some future point of time. Wasps may not be similar in their reproductive abilities and those who are less fertile might be joining others who are more fertile. Testing such a hypothesis would require that individuals who have chosen to be subordinate cofoundresses in multiple foundress associations are forced to nest alone. During this study a total of 77 nests was monitored. Cofoundresses forced to nest alone had significantly lower productivity than natural solitary foundresses and also queens of multiple foundress nests who were forced to nest alone. This suggested that wasps are not similar either in their reproductive ability or brood rearing ability or both. To ascertain which of the factors was responsible for lower productivity in cofoundresses, productivity of wasps isolated into laboratory cages was compared. There was no significant difference in the productivity of isolated cofoundresses and isolated queens. This suggests that wasps are not subfertile per se but probably differ in their foraging and brood rearing abilities. The certainty with which resources are brought into the nest and therefore, the certainty with which the mean per capita productivity is attained, provides an automatic benefit of group living according to the central limit theorem. This prediction was also tested. The coefficient of variation of mean per capita productivity decreased significantly with increasing foundress numbers. Behavioural observations on another 36 colonies, with different number of adults, showed that the coefficient of variation of food brought to the nest and the rate at which larvae were fed, decreased significantly with increasing number of adults. A computer simulation was used to find out the effect of group size on the variance in feed larva. Assuming that larvae cannot be starved for too long and cannot utilize more than a certain amount of food at a time, the fitness of larvae was found to increase with an increase in the number of adults attending the nest. Previous work on R. marginata has been largely confined to postemergence colonies. An attempt was made to look at and compare social organization in preemergence colonies with that of postemergence colonies. It was found that the egg layer was not the most dominant animal in the well-established preemergence colonies. There were no detectable differences in the social organization of the preemergence colonies (of this study) with that of postemergence colonies of the earlier studies. Perhaps my conclusions drawn from studying preemergence colonies are therefore applicable more widely to the species. It can be concluded that the apparent increased fitness of the worker strategy over solitary foundress strategy does not come from any increase in per capita productivity, but comes instead from (i) the greater predictability with which the mean per capita productivity is attained in larger colonies, (ii) the lower probabilities of usurpation of larger colonies, (iii) queen turnovers that provide opportunities for workers in multiple foundress colonies to gain some direct individual fitness and (iv) the lower brood rearing abilities of workers in multiple foundress nests that make the worker strategy the best of a bad job.

Social insects are ecologically dominant because of their specialized, cooperative castes. Reproductive queens lay eggs, while workers take part in brood rearing, nest defense, and foraging. These cooperative castes are a prime example of phenotypic plasticity, whereby a single genetic code gives rise to variation in form and function based on environmental differences. Thus, social insects are well suited for studying mechanisms which give rise to and maintain phenotypic plasticity. At the molecular level, phenotypic plasticity coincides with the differential expression of genes. This dissertation examines the molecular evolution of genes with differential expression between discrete phenotypic or environmental contexts, represented chiefly by female queen and worker castes in social insects. The studies included herein examine evolution at three important levels of biological information: (i) gene expression, (ii) modifications to DNA in the form of methylation, and (iii) protein-coding sequence. From these analyses, a common theme has emerged: genes with differential expression among castes frequently exhibit signatures of relaxed selective constraint relative to ubiquitously expressed genes. Thus, genes associated with phenotypic plasticity paradoxically exhibit modest importance to overall fitness but exceptional evolutionary potential, as illustrated by the success of the social insects.

Bees are aculeate hymenopterans, which, altogether, comprise approximately 20,000 valid species divided into seven families, among which Apidae is one of the best known groups. In addition to the species richness, a remarkable diversity of social behaviors is known to exist within this group, ranging from strict solitary taxa (over 80% of bee species) to groups showing highly sophisticated behaviors related to life in society. One of the most fascinating groups of bees in this respect is that of corbiculate bees (Apidae: Apinae: Apini). Amongst its four subtribes, Apina and Meliponina comprise the so-called \"fixed-caste eusocial\" groups. Phylogenetic relationships of corbiculate bees have been under intense controversy for the last two decades, thus hampering a robust understanding of the evolution of eusocial traits. Most hypotheses based on morphological/behavioral data point to a clade uniting Apina + Meliponina, thus favoring a single origin scenario for the evolution of fixed-caste eusociality. Molecular datasets, on the other hand, consistently indicated independent origins for this cluster of traits. In this contribution, the main goal was to re-evaluate the phylogenetic relationships between the major lineages of corbiculate bees exploring new sources of information from internal skeletal structures of exoskeleton. It were provided descriptions/discussions on some important morphological complexes of the head capsule, mandibles, sitophore, propectus, meso/metafurca and mesophragma of bees. Also, it was attempted to standardize the current morphological terminology used for bees to that used for other Hymenoptera. A set of different phylogenetic analysis with the main lineages of Apidae emphasizing the corbiculate clade was conducted. The complete morphological matrix with 93 characters from external morphology and 42 from internal structures of exoskeleton resulted into two most parsimonious trees with 376 steps, CI=45 and RI=78, which were congruent with the current morphological/behavioral scenario for the corbiculate relationships: Euglossina + (Bombina + (Apina + Meliponina)). It was demonstrated that characters extracted from internal structures of exoskeleton, although poorly explored, can provide critical evidence to elucidate the corbiculate controversy. Moreover, despite the inclusion of new sources of data is fundamental to elucidate this issue, some efforts should be made to reevaluate many characters currently in (re)use. Also, the inclusion of fossil information and use of new technologies for phenotypic studies can open new windows for future comparative morphological studies in bees
Abelhas são himenópteros aculeados que, ao todo, compreendem aproximadamente 20.000 espécies válidas distribuídas em sete famílias, das quais Apidae é um dos grupos mais conhecidos. Além da diversidade de espécies, uma notável diversidade de comportamentos sociais é conhecida para esse grupo, desde táxons estritamente solitários (mais de 80% das espécies de abelhas) a grupos exibindo comportamentos altamente sofisticados relacionados à vida em sociedade. Um dos grupos mais fascinantes nesse aspecto é o das abelhas corbiculadas (Apidae: Apinae: Apini). Dentre suas quatro subtribos, Apina e Meliponina compreendem os chamados grupos eussociais de casta-fixa. As relações filogenéticas entre abelhas corbiculadas têm estado sob intensa controvérsia nas duas últimas décadas, o que dificulta a compreensão robusta da evolução dos atributos da eussocialidade. A maioria das hipóteses baseadas em dados morfológicos/comportamentais apontam para um clado unindo Apina + Meliponina, portanto favorecendo um cenário de origem única para a eusocialidade de casta-fixa. Conjuntos de dados moleculares, por outro lado, indicam consistentemente origens independentes para esse conjunto de atributos. Nesta contribuição, o objetivo principal foi reavaliar as relações filogenéticas entre as principais linhagens de abelhas corbiculadas, explorando novas fontes de informação das estruturas internas do exoesqueleto. Foram fornecidas descrições/discussões sobre alguns importantes complexos morfológicos da cabeça, mandíbulas, sitóforo, meso/metafurca e mesofragma de abelhas. Além disso, buscou-se padronizar a atual terminologia morfológica usada para abelhas com aquela usada para outros Hymenoptera. Um conjunto de diferentes análises com as principais linhagens de Apidae, enfatizando o clado das corbiculadas, foi conduzido. A matrix morfológica completa com 93 caracteres de morfologia externa e 42 de estruturas internas do exoesqueleto resultou em duas árvores mais parcimoniosas com 376 passos, CI=45 e RI=78, que são congruentes com o cenário morfológico/comportamental atual para as relações filogenéticas das corbiculadas: Euglossina + (Bombina + (Apina + Meliponina)). Foi demonstrado que caracteres de estruturas internas do exoesqueleto, apesar de pouco explorados, podem fornecer evidências críticas para elucidar a controvérsia das corbiculadas. Ademais, apesar da inclusão de novas fontes de dados ser fundamental para essa questao, algum esforço deve ser feito para se reavaliar muitos caracteres atualmente em (re)uso. Além disso, a inclusão de informação de fósseis e uso de novas tecnologias para estudos fenotípicos podem abrir novas janelas para futuros estudos morfológicos em abelhas

The evolution of nonreproductive castes is a defining characteristic of eusociality. The function and developmental regulation of the altruistic worker and soldier caste is the central element contributing to major advantages of eusociality over solitary animals. The soldier caste is the first evolved sterile caste in termites. Their primary function is believed to be colony defense. However, the function and development of termite soldiers remains largely unknown. Because of their apparent morphological adaptation for fighting and their limited behavior repertoire, our understanding of colony defense by termite soldiers is limited to their physical defense. In addition, we know little about the molecular mechanisms mediating soldier development. In Chapters 2 and 3 I discuss the role of the soldier caste under competition risk. By exposing the Eastern subterranean termite Reticulitermes flavipes to cues of a competitor termite species, I found that exposure to competitor cues reduced feeding, compromised growth and survival of R. flavipes workers. The presence of R. flavipes soldiers largely ameliorated these negative impacts. At the transcriptional level, R. flavipes soldiers can counteract the effects of competitor cues on worker head gene expression. This counteracting effect seems to be associated with genes in metabolism and immunity. These studies demonstrate that competition can affect a termite colony’s fitness by either competitors physically invading the colony and causing damage or cues from competitors inducing a stress response in termite colony members. More importantly, soldiers can contribute to colony fitness by physically engaging in combat, but also by enhancing colony members’ survival under competitor-cue exposure. In Chapter 4, I describe the molecular mechanism mediating soldier-caste differentiation. I cloned the full length cDNA sequence of the R. flavipes Methoprene-tolerance (Met) gene, a gene encoding a putative receptor for juvenile hormones. Using RNA interference, I studied the function of Met and found that this gene essentially mediates the JH-dependent soldier-caste differentiation in termites.

The social mole-rats have often been typecast as extreme examples of mammalian sociality. With their pronounced reproductive skew, status-related contrasts in lifespan and morphology, and the suggestion of a division of labour amongst helpers, mole-rat societies have repeatedly been likened to the structurally complex societies of some eusocial insects. However, because few studies of mole-rats have quantified individual variation in growth and behaviour across long periods of development, it has remained unclear the extent to which mole-rat societies, and the features of individuals within them, should be considered unique amongst social vertebrates. In this thesis, I examine life history variation in Damaraland mole-rats Fukomys damarensis from three perspectives- growth, behaviour, and ageing- to explore how individual developmental trajectories contribute to, and are influenced by, the structure of mole-rat societies. First, I use a large longitudinal dataset to test for the presence of behavioural specialisation in non-breeding mole-rat helpers. I find no indication of individual specialisation in cooperative activities. Instead, individual differences in helping behaviour are largely the result of age-related changes in the extent to which individuals commit to all forms of helping (Chapter 3); refuting the notion of helper castes. I then focus on the variation in growth across non-breeders, developing a novel biphasic model to accurately quantify sex differences in growth and explore the influence of social effects on growth trajectories (Chapter 4). Despite the proposition of intense intrasexual competition in mole-rat societies, there was no clear signature of sex-specific competition on helper growth trajectories. A more conspicuous form of socially-mediated growth in mole-rats is the secondary growth spurt displayed by females that have acquired the dominant breeding position, causing them to become larger and more elongated. By experimentally controlling reproduction in age-matched siblings, I show that rather than being stimulated by the removal from reproductive suppression, this adaptive morphological divergence is achieved through a lengthening of the lumbar vertebrae when breeding is commenced (Chapter 5). With contrasts in size and shape following the acquisition of the breeding role, this status-related growth pattern shares similarities with growth in naked mole-rats and other social vertebrates. Breeders also show a twofold greater lifespan than non-breeders in Fukomys mole-rats, prompting the suggestion that the transition to dominance also sets individuals onto a slower ageing trajectory. To date, there is little evidence to support a physiological basis to lifespan extension in breeders. This assertion is bolstered by the absence of longer telomeres or slower rates of telomere attrition in breeding females compared to non-breeding females residing in groups (Chapter 6), each of which might be expected if breeders age more slowly. I argue that previous studies exploring status-related ageing in captive Fukomys mole-rats have overlooked the importance of demographic processes (and associated behavioural influences) on mortality schedules. Irrespective of the proximate basis of the longer lifespan of breeders, at an interspecific level the social mole-rats are unusually long-lived for their size. A recent large-scale comparative analysis concluded that prolonged lifespan is a general characteristic of all mammalian cooperative breeders, but this conclusion is premature, as in most of the major clades containing both cooperative and non-cooperative species there is no consistent trend towards lifespan extension in cooperative species (Chapter 7). In the case of mole-rats, it seems more likely that their exceptional longevity arises principally from their subterranean habits and related reductions in extrinsic mortality. Overall, these findings demonstrate that cooperative breeding has important consequences for individual life histories, but there is no strong basis for the claim that Damaraland mole-rat societies are markedly different in form than other cooperative breeding societies.

Soldier caste is the oldest altruistic caste in termites, highly specialized for defensive tasks. Therefore, a number of adaptations in anatomy and behaviour can be observed in soldier, lacking in other termite castes. The aim of this study was to verify the hypothesis that in disturbed groups the soldiers will prefer to stand by and defend the reproductives, the most valuable individuals. Therefore, I studied in two species of the genus Prorhinotermes (P. simplex and P. canalifrons) the ability of soldiers to discriminate neotenic reproductives and provide them with defence. In agreement with the initial hypothesis, the soldiers of both species prooved to be able of an instantaneous recognition of reproductives and remained close to them. In P. simplex, the neotenic female was the most attractive individual, while in P. canalifrons, neotenics of both sexes were equally attractive. The observed preference of reproductives appears to occur only with a certain age of the reproductives in incipient colonies, along with their sexual maturation. Caste specificity of cuticular lipids supports the presumption that the caste recognition is based on olphactoric cues in the cuticle of reproductives.

The work presents life and work of Vladimir Jan Amos Novak, it shows his main thoughts unified by the principle of sociogenesis and points at its inspiration in older traditions of german and russian biology. It also concerns his anthropology as related to the principle of sociogenesis and shows some peculiar Novak's contributions, mainly his opinions on progessive neotenization of man and evolutionary tedency for association. It grasps the principle of sociogenesis as a biological and also a political concept and therefore shows its very political consequences presented mainly on his social thoughts. The work also deals with the relations between eastern and western science on Novák's efforts to unify all sciences under one universal evolutionary framework regardless its geographical belonging. Throughout the work is Novak shown in the context of man-animal relations and the principle of sociogenesis as arising from myrmecological studies. There are therefore presented anthropological works of three important myrmecologists A. Forel, W.M. Wheeler and E.O. Wilson as inspired in the study of ants.

The present study examined social status and adult neurogenesis in the naked mole rat. These animals live in large colonies with a strict reproductive dominance hierarchy; one female and 1-3 males breed, while other members are subordinate and reproductively suppressed. We examined whether social status affects doublecortin (DCX; a marker for immature neurons) immunoreactivity in the dentate gyrus, piriform cortex (PCx), and basolateral amygdala (BLA) by comparing breeders to subordinates. We also examined subordinates removed from their colony and paired with opposite- or same-sex conspecifics for 6 months. Breeders had reduced DCX immunoreactivity in all areas, with BLA effects confined to females. Effects of housing condition were region-specific, with higher PCx DCX immunoreactivity observed in opposite- than same-sex paired subordinates regardless of gonadal status. The opposite pattern was observed in the BLA. Future work will clarify whether findings are attributable to status differences in stress, behavioural plasticity, or life stage.

This thesis has looked at the proximate mechanisms by which eusociality is maintained in colonies of the primitively eusocial wasp Ropalidia marginata. Unlike other typical primitively eusocial species, the R, marginata queen is remarkably docile and non-interactive and hence cannot possibly use aggression to maintain her status. Recent evidence hints at pheromonal queen signalling through the Dufour’s gland. Hence, queen-worker difference in Dufour’s gland composition has been studied in details. Queens and workers differ with respect to overall composition of Dufour’s glands, categories of compounds, and individual compounds as well. The Dufour’s gland compounds may be having a bouquet effect in queen signalling, with individual compounds being less important than the overall composition. The queen pheromone also appears to be an honest signal of fertility, as compounds that differ consistently between queens and workers are correlated with ovarian development of queens, and solitary foundresses and potential queens, who are intermediate between queens and workers in ovarian development, are intermediate in their Dufour’s gland profile as well. When the queen is removed from a colony, one of the workers (potential queen, PQ) shows high aggression, and if the queen is not returned, goes on to become the next queen of the colony. The aggression of PQ comes down as a function of time since queen removal, and correlated with this, the ovaries of PQ increase. Dufour’s gland profile of PQ is similar to workers immediately after queen removal, but comes closer to queens with passage of time. This hints at an interesting transition in maintenance of eusociality from “queen control” by aggression to “queen signal” by pheromone during the queen establishment phase. It has generally been assumed that one set of chemicals can carry multiple information, namely queen signal and colony signal. Initial statistical analysis of chemical composition data showed that perhaps both caste and colony signals can be conveyed by the Dufour’s gland compounds, but detailed analysis cast some doubt on this, as the Dufour’s gland compounds could not be separated into non-overlapping subsets with respect to importance in caste and colony discrimination. A bioassay showed that the wasps do not make colony discrimination from Dufour’s gland compounds. This suggests that the ability to statistically differentiate groups of organisms from their chemical profiles does not guarantee similar discrimination by the organisms themselves, emphasising the need for bioassays to resolve such issues.

This thesis has looked at the proximate mechanisms by which eusociality is maintained in colonies of the primitively eusocial wasp Ropalidia marginata. Unlike other typical primitively eusocial species, the R, marginata queen is remarkably docile and non-interactive and hence cannot possibly use aggression to maintain her status. Recent evidence hints at pheromonal queen signalling through the Dufour’s gland. Hence, queen-worker difference in Dufour’s gland composition has been studied in details. Queens and workers differ with respect to overall composition of Dufour’s glands, categories of compounds, and individual compounds as well. The Dufour’s gland compounds may be having a bouquet effect in queen signalling, with individual compounds being less important than the overall composition. The queen pheromone also appears to be an honest signal of fertility, as compounds that differ consistently between queens and workers are correlated with ovarian development of queens, and solitary foundresses and potential queens, who are intermediate between queens and workers in ovarian development, are intermediate in their Dufour’s gland profile as well. When the queen is removed from a colony, one of the workers (potential queen, PQ) shows high aggression, and if the queen is not returned, goes on to become the next queen of the colony. The aggression of PQ comes down as a function of time since queen removal, and correlated with this, the ovaries of PQ increase. Dufour’s gland profile of PQ is similar to workers immediately after queen removal, but comes closer to queens with passage of time. This hints at an interesting transition in maintenance of eusociality from “queen control” by aggression to “queen signal” by pheromone during the queen establishment phase. It has generally been assumed that one set of chemicals can carry multiple information, namely queen signal and colony signal. Initial statistical analysis of chemical composition data showed that perhaps both caste and colony signals can be conveyed by the Dufour’s gland compounds, but detailed analysis cast some doubt on this, as the Dufour’s gland compounds could not be separated into non-overlapping subsets with respect to importance in caste and colony discrimination. A bioassay showed that the wasps do not make colony discrimination from Dufour’s gland compounds. This suggests that the ability to statistically differentiate groups of organisms from their chemical profiles does not guarantee similar discrimination by the organisms themselves, emphasising the need for bioassays to resolve such issues.

In societies where all individuals are reproductively totipotent and yet, at a given time only one of them reproduces, it is interesting to examine the factor(s) that may influence and predict who will be the reproductive. I am investigating various behavioural, morphological and physiological parameters in the primitively eusocial wasp Ropalidia marginata, and their role in determining the current reproductive and her future successors. In several group-living species, especially in primitively eusocial ones, a strong link between behavioural dominance and reproductive dominance is observed. Hence, I am also investigating the possible determinants of behavioural dominance in R. marginata. I have carried out my study on artificially constituted pairs of wasps as well as in natural colonies in laboratory cages, which represent the founding phase and the established phase in the colony cycle, respectively. Chapter 1: Behavioural and Reproductive Dominance in Pairs of R. marginata Age and body size had no effect on behavioural dominance in pairs of R. marginata, whereas prior experience of behavioural dominance affected future dominance status, indicating presence of winner- and loser-effects. Dominance ranks are relatively stable. This is different from what has been found in colonies, where dominance ranks sometimes change on a daily basis. Body size had no effect, whereas age and behavioural dominance had a significant effect on reproductive dominance in pairs, with older individuals and more dominant individuals having a higher probability of becoming the reproductive. Since no relationship was found between age and behavioural dominance, we predict that the underlying mechanisms by which age and behavioural dominance affect reproductive dominance and independent of each other. This study gives a clear indication that age and behavioural dominance are important variables that determine the reproductive individual during the founding phase of the colony. Chapter 2: Comparison of Dominance Indices and Recommendations for their Use When several individuals interact with each other as in colonies, in a differential and sometimes in a preferential manner, it is difficult to attribute dominance ranks to individuals. Dominance indices are employed to simplify these interactions and rank individuals in dominance hierarchies. Since the rationale behind using a particular dominance index is seldom given in behavioural literature, a comparison of three dominance indices was carried out in second part of the thesis. Each index was gauged on how similar are its ranks as compared to other two indices. Indices were also compared based on the number of untied or unique ranks they attributed. The index that gave least number of ties in ranks was assumed to be better than others. In addition to data from R. marginata colonies, I used data from R. cyathiformis colonies (a congeneric species which behaves more like a typical primitively eusocial species), and artificial data sets, to increase variability in the interaction patterns. We found that each of the indices had their own advantages and disadvantages. In species like R. marginata and R. cyathiformis, where only a few pairs show interactions, and among those who do, very few show reversals, Frequency-based Dominance Index (FDI) is the recommended index of choice. Studies like these will help in understanding how dominance indices operate under certain situations before applying them to construct hierarchies. Chapter 3: Behavioural and Reproductive Dominance in Colonies of R. marginata Age does not affect behavioural dominance, whereas winner and loser effects exist in colonies of R. marginata, just as in pairs. When analysed in detail, I found that colonies of R. marginata showed fewer proportion of pairs interacting, and lower frequency/hour/pair of dominance-subordinate interactions as compared to experimentally paired individuals (from 1st chapter). However, the dominance displays and behaviours were much more intense and severe in colonies. After dominance hierarchies are already established in colonies, frequent need to show dominance behaviour may not arise, due to familiarity between interacting individuals. However, since individuals are possibly aware of each others’ strengths due to past interactions, dominance behaviours are much more severe when contests do happen. My results show that there might be some similarities in terms of determinants of behavioural dominance between pairs and colonies, but the expression of behavioural dominance is quite different. From earlier work it was already known that if the queen/reproductive of the colony disappears or is experimentally removed, one of the individuals shows extreme levels of aggression. This individual, referred to as the potential queen (PQ), will go on to become the next queen of the colony. Her behavioural profile, from the emergence till she establishes herself as the next queen have been well studied earlier. What was not known were the factor(s) that determine the identity of the PQ. It was also unclear what happens when the queen as well as the PQ are both removed, simultaneously or in quick succession. To test whether there is a longer reproductive hierarchy in R. marginata, the queen and the first potential queen of a nest were removed. I found that successive potential queens emerged as readily as the first potential queen, and with dominance profiles comparable to the first PQ, indicating that a reproductive hierarchy indeed exists, at least up to five PQ’s. It was also found that these potential queens were acceptable to all other individuals, as there was not a single act of behavioural dominance directed toward any potential queen. It was also observed that all PQs went on to become queens if the previous queen or PQ was not returned. When tested for various morphological, physiological, behavioural and life history traits (factors possibly influencing the position of an individual in the reproductive hierarchy), we found that age is the only variable that emerges as an important predictor of reproductive succession, with older animals having a higher chance to succeed as next queens of the colony, although even age is not an absolute predictor. Unlike in the pairs, in colonies of R. marginata behavioural dominance is not a good predictor of an individual’s ability to be the queen or the potential queens. The four most important findings of my study are: (i) the first demonstration of winner and loser effects in social insects; (ii) the demonstration that behavioural dominance influences reproductive dominance in pairs but not in colonies; (iii) demonstration of a long reproductive queue among individuals of a colony; and (iv) discovering that age is an important predictor of the identity of the queen and the future queens of the colony. I believe these findings will add significantly to our growing knowledge of the social biology of R. marginata. Finally, my work shows that pairs of R. marginata, representing the founding phase of the colony, behave more like a typical primitively eusocial species, whereas colonies which represent the established phase of the colony cycle behave more like highly eusocial species. Finding the characters of two different forms of sociality in the same species in different phases of the colony cycle makes R. marginata an excellent model system to study evolution of eusociality.

In societies where all individuals are reproductively totipotent and yet, at a given time only one of them reproduces, it is interesting to examine the factor(s) that may influence and predict who will be the reproductive. I am investigating various behavioural, morphological and physiological parameters in the primitively eusocial wasp Ropalidia marginata, and their role in determining the current reproductive and her future successors. In several group-living species, especially in primitively eusocial ones, a strong link between behavioural dominance and reproductive dominance is observed. Hence, I am also investigating the possible determinants of behavioural dominance in R. marginata. I have carried out my study on artificially constituted pairs of wasps as well as in natural colonies in laboratory cages, which represent the founding phase and the established phase in the colony cycle, respectively. Chapter 1: Behavioural and Reproductive Dominance in Pairs of R. marginata Age and body size had no effect on behavioural dominance in pairs of R. marginata, whereas prior experience of behavioural dominance affected future dominance status, indicating presence of winner- and loser-effects. Dominance ranks are relatively stable. This is different from what has been found in colonies, where dominance ranks sometimes change on a daily basis. Body size had no effect, whereas age and behavioural dominance had a significant effect on reproductive dominance in pairs, with older individuals and more dominant individuals having a higher probability of becoming the reproductive. Since no relationship was found between age and behavioural dominance, we predict that the underlying mechanisms by which age and behavioural dominance affect reproductive dominance and independent of each other. This study gives a clear indication that age and behavioural dominance are important variables that determine the reproductive individual during the founding phase of the colony. Chapter 2: Comparison of Dominance Indices and Recommendations for their Use When several individuals interact with each other as in colonies, in a differential and sometimes in a preferential manner, it is difficult to attribute dominance ranks to individuals. Dominance indices are employed to simplify these interactions and rank individuals in dominance hierarchies. Since the rationale behind using a particular dominance index is seldom given in behavioural literature, a comparison of three dominance indices was carried out in second part of the thesis. Each index was gauged on how similar are its ranks as compared to other two indices. Indices were also compared based on the number of untied or unique ranks they attributed. The index that gave least number of ties in ranks was assumed to be better than others. In addition to data from R. marginata colonies, I used data from R. cyathiformis colonies (a congeneric species which behaves more like a typical primitively eusocial species), and artificial data sets, to increase variability in the interaction patterns. We found that each of the indices had their own advantages and disadvantages. In species like R. marginata and R. cyathiformis, where only a few pairs show interactions, and among those who do, very few show reversals, Frequency-based Dominance Index (FDI) is the recommended index of choice. Studies like these will help in understanding how dominance indices operate under certain situations before applying them to construct hierarchies. Chapter 3: Behavioural and Reproductive Dominance in Colonies of R. marginata Age does not affect behavioural dominance, whereas winner and loser effects exist in colonies of R. marginata, just as in pairs. When analysed in detail, I found that colonies of R. marginata showed fewer proportion of pairs interacting, and lower frequency/hour/pair of dominance-subordinate interactions as compared to experimentally paired individuals (from 1st chapter). However, the dominance displays and behaviours were much more intense and severe in colonies. After dominance hierarchies are already established in colonies, frequent need to show dominance behaviour may not arise, due to familiarity between interacting individuals. However, since individuals are possibly aware of each others’ strengths due to past interactions, dominance behaviours are much more severe when contests do happen. My results show that there might be some similarities in terms of determinants of behavioural dominance between pairs and colonies, but the expression of behavioural dominance is quite different. From earlier work it was already known that if the queen/reproductive of the colony disappears or is experimentally removed, one of the individuals shows extreme levels of aggression. This individual, referred to as the potential queen (PQ), will go on to become the next queen of the colony. Her behavioural profile, from the emergence till she establishes herself as the next queen have been well studied earlier. What was not known were the factor(s) that determine the identity of the PQ. It was also unclear what happens when the queen as well as the PQ are both removed, simultaneously or in quick succession. To test whether there is a longer reproductive hierarchy in R. marginata, the queen and the first potential queen of a nest were removed. I found that successive potential queens emerged as readily as the first potential queen, and with dominance profiles comparable to the first PQ, indicating that a reproductive hierarchy indeed exists, at least up to five PQ’s. It was also found that these potential queens were acceptable to all other individuals, as there was not a single act of behavioural dominance directed toward any potential queen. It was also observed that all PQs went on to become queens if the previous queen or PQ was not returned. When tested for various morphological, physiological, behavioural and life history traits (factors possibly influencing the position of an individual in the reproductive hierarchy), we found that age is the only variable that emerges as an important predictor of reproductive succession, with older animals having a higher chance to succeed as next queens of the colony, although even age is not an absolute predictor. Unlike in the pairs, in colonies of R. marginata behavioural dominance is not a good predictor of an individual’s ability to be the queen or the potential queens. The four most important findings of my study are: (i) the first demonstration of winner and loser effects in social insects; (ii) the demonstration that behavioural dominance influences reproductive dominance in pairs but not in colonies; (iii) demonstration of a long reproductive queue among individuals of a colony; and (iv) discovering that age is an important predictor of the identity of the queen and the future queens of the colony. I believe these findings will add significantly to our growing knowledge of the social biology of R. marginata. Finally, my work shows that pairs of R. marginata, representing the founding phase of the colony, behave more like a typical primitively eusocial species, whereas colonies which represent the established phase of the colony cycle behave more like highly eusocial species. Finding the characters of two different forms of sociality in the same species in different phases of the colony cycle makes R. marginata an excellent model system to study evolution of eusociality.