Contracts, Reference Points, and Competition - Behavioral Effects of the Fundamental Transformation

In this paper we study the role of incomplete ex ante contracts for ex post trade. Previous experimental evidence indicates that a contract provides a reference point for entitlements when the terms are negotiated in a competitive market. We show that this finding no longer holds when the terms are determined in a non-competitive way. Our results imply that the presence of a "fundamental transformation" (i.e., the transition from a competitive market to a bilateral relationship) is important for a contract to become a reference point. To the best of our knowledge this behavioral aspect of the fundamental transformation has not been shown before.

Adaptive diversity in heterogeneous environments for populations regulated by a mixture of soft and hard selection

The stable co-existence of two haploid genotypes or two species is studied in a spatially heterogeneous environment submitted to a mixture of soft selection (within-patch regulation) and hard selection (outside-patch regulation) and where two kinds of resource are available. This is analysed both at an ecological time-scale (short term) and at an evolutionary time-scale (long term). At an ecological scale, we show that co-existence is very unlikely if the two competitors are symmetrical specialists exploiting different resources. In this case, the most favourable conditions are met when the two resources are equally available, a situation that should favour generalists at an evolutionary scale. Alternatively, low within-patch density dependence (soft selection) enhances the co-existence between two slightly different specialists of the most available resource. This results from the opposing forces that are acting in hard and soft regulation modes. In the case of unbalanced accessibility to the two resources, hard selection favours the most specialized genotype, whereas soft selection strongly favours the less specialized one. Our results suggest that competition for different resources may be difficult to demonstrate in the wild even when it is a key factor in the maintenance of adaptive diversity. At an evolutionary scale, a monomorphic invasive evolutionarily stable strategy (ESS) always exists. When a linear trade-off exists between survival in one habitat versus that in another, this ESS lies between an absolute adjustment of survival to niche size (for mainly soft-regulated populations) and absolute survival (specialization) in a single niche (for mainly hard-regulated populations). This suggests that environments in agreement with the assumptions of such models should lead to an absence of adaptive variation in the long term.

Corticosterone promotes scramble competition over sibling negotiation in Barn Owl nestlings (Tyto alba)

In species with parental care, siblings compete for access to food resources. Typically, they vocally signal their level of need to each other and to parents, and jostle for the position in the nest where parents deliver food. Although food shortage and social interactions are stressful, little is known about the effect of stress on the way siblings resolve the conflict over how food is shared among them. Because glucocorticoid hormones mediate physiological and behavioral responses to stressors, we tested whether corticosterone, the main glucocorticoid in birds, modulates physical and vocal signaling used by barn owl siblings (Tyto alba) to compete for food. Although corticosterone-implanted (cort-) nestlings and placebo-nestlings were similarly successful to monopolize food, they employed different behavioral strategies. Compared to placebo-nestlings, cort-individuals reduced the rate of vocally communicating with their siblings (but not with their parents) but were positioned closer to the nest-box entrance where parents predictably deliver food. Therefore, corticosterone induced nestlings to increase their effort in physical competition for the best nest position at the expense of investment in sib-sib communication without modifying vocal begging signals directed to parents. This suggests that in the barn owl stress alters nestlings' behavior and corticosterone could mediate the trade-off between scramble competition and vocal sib-sib communication. We conclude that stressful environments may prevent the evolution of sib-sib communication as a way to resolve family conflicts peacefully.

Ecological and historical drivers of diversification in the fly genus Chiastocheta Pokorny.

Coevolution is among the main forces shaping the biodiversity on Earth. In Eurasia, one of the best-known plant-insect interactions showing highly coevolved features involves the fly genus Chiastocheta and its host-plant Trollius. Although this system has been widely studied from an ecological point of view, the phylogenetic relationships and biogeographic history of the flies have remained little investigated. In this integrative study, we aim to test the monophyly of the five Chiastocheta eco-morphological groups, defined by Pellmyr in 1992, by inferring a mitochondrial phylogeny. We further apply a new approach to assess the effect of (i) different molecular substitution rates and (ii) phylogenetic uncertainty on the inference of the spatio-temporal evolution of the group. From a taxonomic point of view, we demonstrate that only two of Pellmyr's groups (rotundiventris and dentifera) are phylogenetically supported, the other species appearing para- or polyphyletic. We also identify the position of C. lophota, which was not included in previous surveys. From a spatio-temporal perspective, we show that the genus arose during the Pliocene in Europe. Our results also indicate that at least four large-scale dispersal events are required to explain the current distribution of Chiastocheta. Moreover, each dispersal to or from Asia is associated with a host-shift and seems to correspond to an increase in speciation rates. Finally, we highlight the correlation between diversification and climatic fluctuations, which indicate that the cycles of global cooling over the last million years had an influence on the radiation of the group.

Characterising avian haemosporidian communities : ecological factors, parasite persistence and co-infection

Les parasites jouent un rôle clef dans l'évolution des comportements et des traits d'histoire de vie de leurs hôtes. Le parasitisme s'avère parfois dévastateur à l'échelle de population d'hôtes, et peut également altérer certains traits associés à la valeur sélective d'un individu infecté, tels que son succès reproducteur ou encore son taux de mortalité. La coévolution hôte/parasite, qui représente l'une des forces sélectives les plus puissantes dans l'évolution des organismes, peut également conduire les partenaires de l'association parasitaire à s'adapter localement à des environnements hétérogènes. Cette thèse porte sur l'étude de parasites aviaires, du genre Plasmodium, Haemopro- teus et Leucocytozoon (Haemosporidae), naturellement associés à différentes populations de mésanges charbonnières (Parus major) et d'hirondelles des fenêtres (Delichon ur- bicum). Dans un premier temps, nous avons cherché à déterminer comment se distribuent ces parasites au sein de différentes populations hôtes et si ces communautés de parasites sont structurées. Par la suite, la principale question à laquelle nous voulions répondre était de savoir comment ces parasites, et notamment après coexistence de plusieurs lignées génétiques d'Haemosporidae au sein dun même-individu (i.e. co-infection), affectent la physiologie et le succès de reproducteur des hôtes. Nos résultats suggèrent que la distribution des Haemosporidae est principalement gouvernée par la présence d'insectes vecteurs et que la persistance de l'infection chez les hôtes varie en fonction du genre d'Haemosporidae (Chapitre 1-2). Par ailleurs, nous avons trouvé que des lignées de parasite génétiquement distinctes peuvent avoir des effets contrastés sur leurs hôtes. Par exemple, les hôtes exhibent des différences de parasitémie marquées en fonction des lignées de parasites responsable de l'infection. De plus, le succès reproducteur ainsi que la charge parasitaire des mésanges infectées par Plasmodium ou Haemoproteus n'étaient pas affecté par l'infection simultanée avec Leucocytozoon (Chapitre 2-3). Dans le Chapitre 4, j'ai examiné la capacité immunitaire de mésanges charbonnières infectées par des hémosporidies. Les résultats n'ont pas été concluant, et je suggère fortement une réévaluation de ceux-ci dans de futures études. Les mésanges charbonnières ne semblent pas signaler leur statut infectieux par la coloration de leur plumage (Chapitre 5); toutefois, la coloration noire des plumes reflète l'état de stress oxydatif des mésanges, qui dépend lui-même de l'infection parasitaire. La coloration verte pourrait également indiquer la qualité des soins paxentaux délivrés par les mésanges adultes femelles à leurs petits, comme le suggère la corrélation que nous avons observée entre la masse des jeunes d'une nichée et la coloration de leur mère. Les hirondelles capturées en Algérie souffrent plus de l'infection que celles échantillon¬nées en Europe (Chapitre 6). Les similitudes observées entre les communautés de par¬asites affectant les populations européennes et celles des populations nord-africaines suggèrent que la transmission des parasites a lieu lors de la migration vers le sud. A l'instar de nos observations sur les mésanges dans les chapitres 2 et 3, les hirondelles co-infectées ne montrent pas d'altérations de leur condition physique. Cette thèse démontre qu'il existe, au sein des populations de mésanges charbonnières, des interactions antagonistes entre, d'une part, les parasites et leurs hôtes et d'autre part, entre différent parasites. Le résultat de ces interactions antagonistes varie en fonction des espèces et de la zone géographique considérée. Nous avons démontré que les interactions ne suivent pas toujours la théorie, puisque la coevolution qui, en suivant le concept de la virulence, devrait augmenter la charge parasitaire et diminuer la condition physique des hôtes, ne montre pourtant pas d'impact négatif sur les populations de mésanges. Nous pouvons maintenant concentrer nos efforts à la caractérisation des interactions antagonistes. De plus, grâce aux avancées des méthodes moléculaires, nous pouvons suivre et étudier en détails comment ces interactions se manifestent et quels sont leurs effets sur la condition physique des hôtes. - Parasites are key in shaping various behavioural and life-history traits of their hosts. The influence of parasitism on host populations varies from slight to devastating and might influence such parameters as mortality rates or reproductive success. Host-parasite coevolution is one of the most powerful selective forces in evolution and can lead to local adaptation of parasites and hosts in spatially structured environments. In this thesis, I studied haemosporidian parasites in different populations of great tits (Parus major) and house martins (Delichon urbicum). Firstly, I wanted to determine how parasites are distributed and if parasite communities are structured. The main question I wanted to address hereafter was how parasites, and specifically infection with multiple genera of parasites (i.e. co-infection) influenced host physiology and reproductive success. I found that parasite distribution is environmentally driven and could therefore be closely linked to vector prevalence; and that the stability of parasite infection over time is genus-dependent (Chapter 1 - 2). I further found that different haemosporidian lineages might interact differently with their hosts as parasitaemia was strongly lineage-specific and that the presence of Leucocytozoon parasites showed no correlation to Plasmodium or Haemoproteus parasitaemia, nor to great tit reproductive success (Chapter 2-3). In Chapter 4 I examined immune capacity of haemosporidian-infected great tits. The results proved inconclusive, and I strongly suggest re-evaluation hereof in future work. Great tits do not appear to signal parasite infection through plumage colouration (Chapter 5); however, infection did have a link to oxidative stress resistance which is strongly signalled through the black breast stripe, with darker males being more resistant and darker females less resistant. Females might incur different costs associated with darker stripes. This would allow reversal of signaling function. Green colouration could also serve as a cue for female provisioning quality as indicated by the strong correlation between colouration and chick body mass. Breeding house martins caught in Algeria suffer greater haemosporidian infection than European populations (Chapter 6). Similar parasite communities in European and North-African populations suggest transmission of parasites may occur during southward migration. Similarly to what was observed in great tits in Chapter 2 and 3, no relationship was found between parasite co-infection and Swiss house martin body condition. This thesis demonstrates that host-parasite and inter-parasite antagonistic interac¬tions exist in great tit populations. How these interactions play out is species dependent and varies geographically. I have demonstrated that interactions do not always follow the theory, as co-infection - which under the concept of virulence should increase parasitaemia and decrease body condition - showed no negative impact on great tit populations. We can now concentrate our efforts on characterising these antagonistic interactions, and with the advance in molecular methods, track and investigate how these interactions play out and what the effect on host fitness is.

The ecological significance of arbuscular mycorrhizal fungal effects on clonal reproduction in plants

The population ecology of clonal plants depends on the number and distribution of ramets formed during growth. Variation in clonal reproduction has previously been explained by variation in effects of abiotic resource heterogeneity and by plant genotypic variation. Different co-occurring species of the mutualistic arbuscular mycorrhizal fungi (AMF) have been shown to differentially alter growth traits of Prunella vulgaris which we hypothesize would lead to changes in clonal reproduction. Two experiments were carried out to test whether different co-occurring mycorrhizal fungi significantly influence clonal reproduction of P. vulgaris whether this effect also occurs when P. vulgaris is growing in an artificial plant community and how the effects compare with plant genotype effects on clonal growth of P. vulgaris. In the first experiment the number of ramets of P. vulgaris growing in a plant community of simulated calcareous grassland was significantly affected by inoculation with different mycorrhizal fungi. The number of ramets produced by P. vulgaris differed by a factor of up to 1.8 with different mycorrhizal fungi. The fungal effects on the number of new ramets were independent of their effects on the biomass of P. vulgaris. In a second experiment 17 different genotypes of P. vulgaris were inoculated with different mycorrhizal fungi. There were significant main effects of genotypes and mycorrhizal fungi on clonal reproduction of P. vulgaris. The effect of different mycorrhizal fungi contributed more than the effect of plant genotype to variation in size and ramet production. However mean stolon length and spacer length which determine the spatial arrangement of ramets were only significantly affected by plant genotype. There were no mycorrhizal fungal X plant genotype interactions on clonal growth of P. vulgaris indicating that there is no obvious evidence that selection pressures would favor further coevolution between P. vulgaris and mycorrhizal fungal species. In natural communities plants can be colonized by several different AMF at the same time. The effect of the mixed AMF treatment on the growth and clonal reproduction of P. vulgaris could not be predicted from the responses of the plants to the single AMF To what extent however the patterns of colonization by different AMF differ among plants in a natural community is unknown. Since the effects of AMF on growth and clonal reproduction occur on a population of P. vulgaris in a microcosm plant community and because the effects are also as great as those caused by plant genotypic variation we conclude that the effects are strong enough to potentially affect population size and variation of clonal plants in communities.

Ecological-economic optimization of biodiversity conservation under climate change

Substantial investment in climate change research has led to dire predictions of the impacts and risks to biodiversity. The Intergovernmental Panel on Climate Change fourth assessment report(1) cites 28,586 studies demonstrating significant biological changes in terrestrial systems(2). Already high extinction rates, driven primarily by habitat loss, are predicted to increase under climate change(3-6). Yet there is little specific advice or precedent in the literature to guide climate adaptation investment for conserving biodiversity within realistic economic constraints(7). Here we present a systematic ecological and economic analysis of a climate adaptation problem in one of the world's most species-rich and threatened ecosystems: the South African fynbos. We discover a counterintuitive optimal investment strategy that switches twice between options as the available adaptation budget increases. We demonstrate that optimal investment is nonlinearly dependent on available resources, making the choice of how much to invest as important as determining where to invest and what actions to take. Our study emphasizes the importance of a sound analytical framework for prioritizing adaptation investments(4). Integrating ecological predictions in an economic decision framework will help support complex choices between adaptation options under severe uncertainty. Our prioritization method can be applied at any scale to minimize species loss and to evaluate the robustness of decisions to uncertainty about key assumptions.

Case studies and mathematical models of ecological speciation. 1. Cichlids in a crater lake.

A recent study of a pair of sympatric species of cichlids in Lake Apoyo in Nicaragua is viewed as providing probably one of the most convincing examples of sympatric speciation to date. Here, we describe and study a stochastic, individual-based, explicit genetic model tailored for this cichlid system. Our results show that relatively rapid (<20,000 generations) colonization of a new ecological niche and (sympatric or parapatric) speciation via local adaptation and divergence in habitat and mating preferences are theoretically plausible if: (i) the number of loci underlying the traits controlling local adaptation, and habitat and mating preferences is small; (ii) the strength of selection for local adaptation is intermediate; (iii) the carrying capacity of the population is intermediate; and (iv) the effects of the loci influencing nonrandom mating are strong. We discuss patterns and timescales of ecological speciation identified by our model, and we highlight important parameters and features that need to be studied empirically to provide information that can be used to improve the biological realism and power of mathematical models of ecological speciation.

Do we fear tax competition among new and old European countries ?

The purpose of this paper is to study both theoretically and empirically tax competition in the enlarged EU and to provide some insights on ongoing reforms concerning business taxation. We support the idea that even if one can observe cuts in "new" members statutory business tax rates, this should not result in fiercer tax competition between the "core" and "the "periphery" since infrastructure endowments and the existence of agglomeration rents in the core of the EU may prevent (at least partially) activities to relocate to the "new" members.

Behavioural types and ecological effects in a natural population of the cooperative cichlid Neolamprologus pulcher

The ecological relevance of behavioural syndromes is little studied in cooperative breeding systems where it is assumed that the behavioural type might influence individual decisions on helping and dispersal (e.g. shy, nonaggressive and nonexplorative individuals remain philopatric and helpful, whereas bold, aggressive, explorative individuals compete for vacancies outside their group and disperse). We measured the behavioural type of 19 subordinates in the cooperatively breeding cichlid fish Neolamprologus pulcher in their natural environment by quantifying six behavioural traits up to four times ('trials') in three different contexts, by presenting them with a conspecific intruder, a predator or nothing inside a tube. We found only moderate within-context repeatability (intraclass correlation coefficients) of the focal individual's behaviour, except for attacking either the conspecific or the predator inside the tube. The focal individual's attack rate of the tube was also positively affected by its group size. Averaging traits per context removed the between-trial variation, and consequently the across-context repeatability was very high for all six traits, except for territory maintenance. Trait values depended significantly on the context, except for territory defence. Consequently, individuals could be classified into different behavioural types based on their reaction towards the tube, but surprisingly, and opposite to laboratory studies in this species, ranging propensity and territory maintenance were not included in this behavioural syndrome. We suggest that more studies are needed to compare standardized focal personality tests (e.g. exploration propensity) with actual behaviour observed in nature (e.g. ranging and dispersal).

Evolutionary and ecological significance of non-shivering thermogenesis in the common vole

La production endogène à long terme de chaleur, même au repos, est une adaptation que l'on retrouve chez les animaux à sang chaud (les oiseaux et les mammifères). Cette production de chaleur a comme but le maintien d'une température constante du corps indépendamment de la température extérieure. A cette fin, les mammifères ont développé une forme de tissu spécialisé nommé tissu adipeux brun (BAT). Ce tissu est responsable de la conversion de nourriture en chaleur, procédé appelé thermogenèse sans frisson (NST = non-shivering thermogenesis). Durant ce procédé la uncoupling protein 1 (UCP1) convertit, au sein des mitochondries, la nourriture en chaleur au lieu de produire de l'ATP, molécule utilisée comme énergie cellulaire. On suppose que cette inefficacité de la conversion de la nourriture en ATP dans le BAT influence l'homéostasie de l'énergie, l'allocation des ressources ainsi que la régulation de processus gourmant en énergie comme la croissance et la reproduction. Afin de maintenir une température du corps constante, les mammifères doivent ajuster leur NST en fonction de la température ambiante. La NST devrait être donc plus importante que la croissance et la reproduction durant l'hiver que lors l'été/à haute altitude qu'à basse altitude. En effet, plusieurs études ont déjà démontré la dépendance de la NST aux divers paramètres environnementaux. Par contre, l'héritabilité de la NST ainsi que sa relation avec d'autres traits de caractère, ne sont que très peu connus, ceci malgré l'importance d'une telle information afin de pouvoir comprendre son potentiel évolutif. L'étude de l'importance évolutive et écologique sur la NST chez les campagnols des champs (Microtus arvalis) fut donc le but cette thèse de doctorat. Grâce aux informations collectées sur 4 générations de campagnols (chapitre 1), une dépendance saisonnière et journalière de la NST a été démontrée: elle augmente lors des périodes froides et diminue lors de la lactation. On a démontré que bien qu'étant plastique, la variation de la NST a une composante génétique significative. Elle est corrélée avec le taux d'activité métabolique au repos indiquant des contraintes intrinsèques. A l'aide d'une expérience de jardin commune, on a pu démontrer dans le chapitre 2 que les campagnols habitant en altitude ont une capacité génétique de thermogenèse sans frisson plus haute que celles de basse altitude. Ils produisent des portées plus petites et leur descendance grandit moins vite, surtout à partir du 10ème jour ce qui coïncide avec le début de la production de chaleur endogène. En choisissant artificiellement des campagnols avec une NST faible ou grande, on a pu démontrer une relation entre la NST et la développement de la masse corporelle. Les campagnols avec une haute NST grandissent plus lentement et sont plus légères à l'âge adulte que celles ayant une basse NST. A l'aide d'un croisement interligne entre les campagnols sélectionnés (avec basse et haute NST), on a pu montrer dans le chapitre 3 des effets « parent-of-origin >> du développement massique de la descendance, indiquant une empreinte génétique parentale. Cela veut dire que l'expression d'un allele dépend de l'origine parentale. De plus, des effets « parent-of-origin » des taux de base de norépinephrine et d'irisine ont pu être trouvés. Ces hormones sont connues pour influencer non seulement la TSF mais aussi d'autres caractéristiques. Ces influences ouvrent la voie à de nouvelles études sur la relation entre la TSF et l'histoire de vie. Dans le chapitre 4 on a démontré des effets à long terme de l'allocation des ressources en manipulant la taille des portées qui ont abouti à des différences dans l'investissement dans la reproduction et de la croissance de la descendance à la fois dans le cas de la reproduction manipulé et aussi dans le non - manipulée entre les femelles avec portées agrandies et réduites. Ensemble, ces résultats mettent en évidence le rôle central de la NST dans l'allocation des ressources sur la base d'un compromis entre le maintien et la croissance et ainsi transforme l'histoire de vie des mammifères. Ces études montrent comment les mammifères peuvent répondre rapidement à court et à long terme (c'est-à-dire par des réponses génétiques ou plastiques) à un changement rapide du climat. On montre aussi qu'il y a probablement une corrélation entre l'histoire de vie et des changements du comportement. Finalement mes résultats ont montré un lien étroit entre la NST et la croissance et les dimensions du corps. Ces résultats indiquent que le tissu adipeux brun et la NST pourraient être une cible thérapeutique intéressante pour traiter l'obésité.

Ecologie trophique de deux espèces jumelles et sympatriques de chauves-souris: Myotis myotis et Myotis blythii (Chiroptera : Vespertilionidae). Premiers résultats

M. myotis and M. blythii are two sibling species of bats that live sympatrically over wide areas of the Western Palearctic region, and which often coexist intimately in their nursery roosts. According to the principle of <<limiting similarity>> this cohabitation should imply an interspecific ecological differentiation. The hypothesis of a niche separation at the trophic level is tested here. The fecal analysis of 300 droppings collected from a zone of sympatry shows a clear interspecific differentiation in diets : M. myotis eats mostly Carabidae (Coleoptera), whereas M. blythii captures essentially Tettigoniidae, Gryllidae and Acrididae (Orthoptera). Because they consume exclusively terrestrial arthropods, M. myotis and M. blythii are typical ground and/or grass gleaning bats. However, despite their narrow niches they are probably not specialized in the predation of only some definite categories of prey. The narrow diets probably reflect the high specialization of their modes of resource exploitation: M. myotis and M. blythii prey upon ground arthropods and they are likely to select for different foraging;g habitats. M. myotis probably prefers wooded feeding grounds (Carabidae) whereas M. blythii exploits herbaceous habitats (Orthoptera). The strong trophic segregation observed in sympatry between M. myotis and M. blythii shows that the interspecific competition is distinctly much weaker than the intraspecific one. This would explain the stable, intimate co-existence of these two virtual competitors.

Peroxisome proliferator-activated receptor mediates cross-talk with thyroid hormone receptor by competition for retinoid X receptor. Possible role of a leucine zipper-like heptad repeat.

The peroxisome proliferator-activated receptors (PPAR) and thyroid hormone receptors (TR) are members of the nuclear receptor superfamily, which regulate lipid metabolism and tissue differentiation. In order to bind to DNA and activate transcription, PPAR requires the formation of heterodimers with the retinoid X receptor (RXR). In addition to activating transcription through its own response elements, PPAR is able to selectively down-regulate the transcriptional activity of TR, but not vitamin D receptor. The molecular basis of this functional interaction has not been fully elucidated. By means of site-directed mutagenesis of hPPAR alpha we mapped its inhibitory action on TR to a leucine zipper-like motif in the ligand binding domain of PPAR, which is highly conserved among all subtypes of this receptor and mediates heterodimerization with RXR. Replacement of a single leucine by arginine at position 433 of hPPAR alpha (L433R) abolished heterodimerization of PPAR with RXR and consequently its trans-activating capacity. However, a similar mutation of a leucine residue to arginine at position 422 showed no alteration of heterodimerization, DNA binding, or transcriptional activation. The dimerization deficient mutant L433R was no longer able to inhibit TR action, demonstrating that the selective inhibitory effect of PPAR results from the competition for RXR as well as possibly for other TR-auxiliary proteins. In contrast, abolition of DNA binding by a mutation in the P-box of PPAR (C122S) did not eliminate the inhibition of TR trans-activation, indicating that competition for DNA binding is not involved. Additionally, no evidence for the formation of PPAR:TR heterodimers was found in co-immunoprecipitation experiments. In summary, we have demonstrated that PPAR selectively inhibits the transcriptional activity of TRs by competition for RXR and possibly non-RXR TR-auxiliary proteins. In contrast, this functional interaction is independent of the formation of PPAR:TR heterodimers or competition for DNA binding.

The evolution of unicoloniality in ant societies : recognition, dispersal and population genetic structure

Introduction Societies of ants, bees, wasps and termites dominate many terrestrial ecosystems (Wilson 1971). Their evolutionary and ecological success is based upon the regulation of internal conflicts (e.g. Ratnieks et al. 2006), control of diseases (e.g. Schmid-Hempel 1998) and individual skills and collective intelligence in resource acquisition, nest building and defence (e.g. Camazine 2001). Individuals in social species can pass on their genes not only directly trough their own offspring, but also indirectly by favouring the reproduction of relatives. The inclusive fitness theory of Hamilton (1963; 1964) provides a powerful explanation for the evolution of reproductive altruism and cooperation in groups with related individuals. The same theory also led to the realization that insect societies are subject to internal conflicts over reproduction. Relatedness of less-than-one is not sufficient to eliminate all incentive for individual selfishness. This would indeed require a relatedness of one, as found among cells of an organism (Hardin 1968; Keller 1999). The challenge for evolutionary biology is to understand how groups can prevent or reduce the selfish exploitation of resources by group members, and how societies with low relatedness are maintained. In social insects the evolutionary shift from single- to multiple queens colonies modified the relatedness structure, the dispersal, and the mode of colony founding (e.g. (Crozier & Pamilo 1996). In ants, the most common, and presumably ancestral mode of reproduction is the emission of winged males and females, which found a new colony independently after mating and dispersal flights (Hölldobler & Wilson 1990). The alternative reproductive tactic for ant queens in multiple-queen colonies (polygyne) is to seek to be re-accepted in their natal colonies, where they may remain as additional reproductives or subsequently disperse on foot with part of the colony (budding) (Bourke & Franks 1995; Crozier & Pamilo 1996; Hölldobler & Wilson 1990). Such ant colonies can contain up to several hundred reproductive queens with an even more numerous workforce (Cherix 1980; Cherix 1983). As a consequence in polygynous ants the relatedness among nestmates is very low, and workers raise brood of queens to which they are only distantly related (Crozier & Pamilo 1996; Queller & Strassmann 1998). Therefore workers could increase their inclusive fitness by preferentially caring for their closest relatives and discriminate against less related or foreign individuals (Keller 1997; Queller & Strassmann 2002; Tarpy et al. 2004). However, the bulk of the evidence suggests that social insects do not behave nepotistically, probably because of the costs entailed by decreased colony efficiency or discrimination errors (Keller 1997). Recently, the consensus that nepotistic behaviour does not occur in insect colonies was challenged by a study in the ant Formica fusca (Hannonen & Sundström 2003b) showing that the reproductive share of queens more closely related to workers increases during brood development. However, this pattern can be explained either by nepotism with workers preferentially rearing the brood of more closely related queens or intrinsic differences in the viability of eggs laid by queens. In the first chapter, we designed an experiment to disentangle nepotism and differences in brood viability. We tested if workers prefer to rear their kin when given the choice between highly related and unrelated brood in the ant F. exsecta. We also looked for differences in egg viability among queens and simulated if such differences in egg viability may mistakenly lead to the conclusion that workers behave nepotistically. The acceptance of queens in polygnous ants raises the question whether the varying degree of relatedness affects their share in reproduction. In such colonies workers should favour nestmate queens over foreign queens. Numerous studies have investigated reproductive skew and partitioning of reproduction among queens (Bourke et al. 1997; Fournier et al. 2004; Fournier & Keller 2001; Hammond et al. 2006; Hannonen & Sundström 2003a; Heinze et al. 2001; Kümmerli & Keller 2007; Langer et al. 2004; Pamilo & Seppä 1994; Ross 1988; Ross 1993; Rüppell et al. 2002), yet almost no information is available on whether differences among queens in their relatedness to other colony members affects their share in reproduction. Such data are necessary to compare the relative reproductive success of dispersing and non-dispersing individuals. Moreover, information on whether there is a difference in reproductive success between resident and dispersing queens is also important for our understanding of the genetic structure of ant colonies and the dynamics of within group conflicts. In chapter two, we created single-queen colonies and then introduced a foreign queens originating from another colony kept under similar conditions in order to estimate the rate of queen acceptance into foreign established colonies, and to quantify the reproductive share of resident and introduced queens. An increasing number of studies have investigated the discrimination ability between ant workers (e.g. Holzer et al. 2006; Pedersen et al. 2006), but few have addressed the recognition and discrimination behaviour of workers towards reproductive individuals entering colonies (Bennett 1988; Brown et al. 2003; Evans 1996; Fortelius et al. 1993; Kikuchi et al. 2007; Rosengren & Pamilo 1986; Stuart et al. 1993; Sundström 1997; Vásquez & Silverman in press). These studies are important, because accepting new queens will generally have a large impact on colony kin structure and inclusive fitness of workers (Heinze & Keller 2000). In chapter three, we examined whether resident workers reject young foreign queens that enter into their nest. We introduced mated queens into their natal nest, a foreign-female producing nest, or a foreign male-producing nest and measured their survival. In addition, we also introduced young virgin and mated queens into their natal nest to examine whether the mating status of the queens influences their survival and acceptance by workers. On top of polgyny, some ant species have evolved an extraordinary social organization called 'unicoloniality' (Hölldobler & Wilson 1977; Pedersen et al. 2006). In unicolonial ants, intercolony borders are absent and workers and queens mix among the physically separated nests, such that nests form one large supercolony. Super-colonies can become very large, so that direct cooperative interactions are impossible between individuals of distant nests. Unicoloniality is an evolutionary paradox and a potential problem for kin selection theory because the mixing of queens and workers between nests leads to extremely low relatedness among nestmates (Bourke & Franks 1995; Crozier & Pamilo 1996; Keller 1995). A better understanding of the evolution and maintenance of unicoloniality requests detailed information on the discrimination behavior, dispersal, population structure, and the scale of competition. Cryptic genetic population structure may provide important information on the relevant scale to be considered when measuring relatedness and the role of kin selection. Theoretical studies have shown that relatedness should be measured at the level of the `economic neighborhood', which is the scale at which intraspecific competition generally takes place (Griffin & West 2002; Kelly 1994; Queller 1994; Taylor 1992). In chapter four, we conducted alarge-scale study to determine whether the unicolonial ant Formica paralugubris forms populations that are organised in discrete supercolonies or whether there is a continuous gradation in the level of aggression that may correlate with genetic isolation by distance and/or spatial distance between nests. In chapter five, we investigated the fine-scale population structure in three populations of F. paralugubris. We have developed mitochondria) markers, which together with the nuclear markers allowed us to detect cryptic genetic clusters of nests, to obtain more precise information on the genetic differentiation within populations, and to separate male and female gene flow. These new data provide important information on the scale to be considered when measuring relatedness in native unicolonial populations.