Cannibalism and conflict in Formica ants

In complex societies like ant colonies individuals cooperate in the aim of maximizing offspring production. But cooperation is only flawless from afar. In fact, because adults can differ in their relatedness to brood they often have contrasting inclusive fitness interests, which may lead to outbreaks of social conflict. However, although conflicts in ant colonies typically arise over offspring production, the role of offspring as actors in social conflict has received little attention. The primary aim of this thesis was to investigate the role of larvae in ant societies, with particular emphasis on selfish larval behavior in the form of egg cannibalism. This thesis demonstrates that Formica ant larvae readily engage in egg cannibalism. Egg consumption allows larvae to increase survival and positively affects the expression of key growth-related genes. Levels of cannibalism across species decrease when relatedness between larvae and eggs is high, which suggests that cannibalism is a selfish trait that can underlie social control. Cannibalism appears to be plastic in F. aquilonia, where levels increase when larvae are presented with foreign eggs compared to sibling eggs. In addition, cannibalism intensity is highly dependent on larvae sex and size across eight species. I conclude that ant larvae are far from powerless. Instead, cannibalism may allow larvae to influence important determinants of individual fitness such as caste fate or size. By consuming eggs, larvae may furthermore affect overall colony fitness. For the first time, this thesis identifies larvae as individuals with selfish interests that have the power to act in social conflict, thus adding a new dimension to our understanding of colony dynamics in social insects. In order to understand how relatedness between individuals potentially impacts conflict in ant societies on a larger scale, this thesis furthermore focuses on the genetic network of native wood ant populations. The societies of these ants consist of many interconnected nests with hundreds of reproductive queens, where individuals move freely between nests and cooperate across nest boundaries. The combination of high queen numbers and free mixing of individuals results in extremely low relatedness within these so-called supercolonies. Here, cooperative worker behavior appears maladaptive because it may aid random individuals instead of relatives. I use network analysis to test for spatial and temporal variation in genetic structure, in order to provide a comprehensive picture of genetic substructure in native wood ant populations. I find that relatedness within supercolonies is low but positive when viewed on a population level, which may be due to limited dispersal range of individuals and ecological factors such as nest site limitation and competition against conspecifics. Genetic network analysis thus provides novel evidence that ant supercolonies can exhibit fine-scale genetic substructure, which may explain the maintenance of cooperation in these low-relatedness societies. Overall, these results offer a new perspective on the stability of cooperation in ant societies, and will hopefully contribute to our understanding of the evolutionary forces governing the balance between cooperation and conflict in other complex social systems.Monimutkaisissa yhteiskunnissa sukulaisuuden aste määrää yksilöiden välisten konfliktien voimakkuuden. Muurahaisten suuri lajienvälinen ja sisäinen vaihtelevuus yhteiskuntien sukulaisuusrakenteessa tekee niistä oivallisen itsekkyyden ja konfliktien tutkimuksen kohteen. Vaikka konfliktit yleensä liittyvät jälkeläisten kasvattamiseen, ei kehittyvien toukkien roolia konfliktin aktiivisina osapuolina ole juuri tutkittu. Väitöskirjassani keskityn toukkien rooliin muurahaisten yhteiskunnissa yleisesti, ja erityisesti toukkien itsekkääseen kannibalistiseen munien syöntiin. Ymmärtääkseni laajemmin sukulaisuuden vaikutukset konflikteihin muurahaisyhteiskunnissa, tutkin lisäksi Formica aquilonia kekomuurahaislajin pesäverkostojen geneettistä rakennetta. Kaikenkaikkiaan väitöskirjani lisää tietämystämme yhteistyön ja konfliktien välisestä tasapainottelusta monimutkaisissa sosiaalisissa yhteisöissä