Browsing by Subject "biology"

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  • Schultner, Eva (Helsingin yliopisto, 2014)
    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.
  • Rankin, Daniel (Helsingin yliopisto, 2007)
    Natural selection generally operates at the level of the individual, or more specifically at the level of the gene. As a result, individual selection does not always favour traits which benefit the population or species as a whole. The spread of an individual gene may even act to the detriment of the organism in which it finds. Thus selection at the level of the individual can affect processes at the level of the organism, group or even at the level of the species. As most behaviours ultimately affect births, deaths and the distribution of individuals, it seems inevitable that behavioural decisions will have an impact on population dynamics and population densities. Behavioural decisions can often involve costs through allocation of energy into behavioural strategies, such as the investment into armaments involved in fighting over resources or increased mortality due to injury or increased predation risk. Similarly, behaviour may act o to benefit the population, in terms of higher survival and increased fecundity. Examples include increased investment through parental care, choosing a mate based on the nuptial gifts they may supply and choosing territories in the face of competition. Investigating the impact of behaviour on population ecology may seem like a trivial task, but it is likely to have important consequences at different levels. For example, antagonistic behaviour may occasionally become so extreme that it increases the risk of extinction, and such extinction risk may have important implications for conservation. As a corollary, any such behaviour may also act as a macroevolutionary force, weeding out populations with traits which, whilst beneficial to the individuals in the short term, ultimately result in population extinction. In this thesis, I examine how behaviours, specifically conflict and competition over a resource and aspects of behaviour involved in sexual selection, can affect population densities, and what the implications are for the evolution and ecology of the populations in question. It is found that both behaviours related to individual conflict and mating strategies can have an effect at the level of the population, but that various factors, such as a feedback between selection and population densities or macroevolution caused by species extinctions, may act to limit the intensity of conflicts that we observe in nature.