The ecology and evolution of sibling cannibalism in the wild

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Cannibalism is a behaviour displayed by nearly all taxonomic groups and it can be divided into several subtypes. The consumption of one's own siblings, sibling cannibalism, presents an interesting case as it entails the somewhat counterintuitive act of eating a relative with whom one shares approximately 50% of its genetic makeup. Understanding the evolutionary and ecological reasons for the degree of sibling cannibalism expressed in a species/individual is a multi-faceted task. Propensity for cannibalism is influenced by several ecological factors (e.g., nutritional benefits and diseases costs) with opposing effects. Additionally, cannibalism propensity can be influenced by the evolutionary fitness costs associated with consuming a relative. Cannibalism levels within a brood may also be influenced by mothers, as within-brood cannibalism can either decrease or increase a mother's evolutionary fitness, depending on the ecological context. Sibling cannibalism can therefore be a source of sibling-sibling and mother-offspring conflict. As well as being a complex and fascinating area of research, studying cannibalism may facilitate further development of knowledge on evolutionary theories such as Hamilton's rule, and can benefit research with economic (e.g., in agriculture) and conservational (in the study of invasive species) importance. To date, research on sibling cannibalism is constrained by the low species diversity of its study species and by its lack of fieldwork-based empirical data. Creating a research framework with greater species diversity may facilitate the construction of a more generalisable knowledge base on what, in an ecological and evolutionary framework, drives cannibalism's prevalence. Possession of such a base could allow future research on cannibalism to progress more effectively, with a greater ease of making predictions. As cannibalistic behaviours may be expressed differently in lab vs. more natural settings it is imperative to increase the amount of work which has been done on cannibalism in the field to see how well laboratory studies can explain the behaviour of wild populations. This project aims to further understand the evolutionary and ecological drivers of sibling cannibalism in insects, specifically in the Lygaeidae (a group of true bugs for whom little sibling cannibalism research has been done) and the Coccinellidae (Ladybirds, a group containing species who may be more efficient invaders due to cannibalism), using a combination of lab and field-based study. Lab work will initially focus on testing ideas of sibling-sibling and mother-offspring conflict over cannibalism, studying the implications of inclusive fitness costs of cannibalism in Lygaeids (and in doing so developing methods to study cannibalism in a previously understudied group) and the involvement of mothers in influencing brood cannibalism levels in both Lygaeids and Coccinellids. The work testing the mother's involvement can also be expanded to consider the heritability of cannibalism and other correlated traits, a subject which has previously garnered little attention from an evolutionary perspective. Fieldwork will include considerations of the influence of surrounding food abundance on cannibalism levels in both Lygaeids and the Coccinellidae, and deduction of the relatedness structure of insect clusters using molecular genetic techniques.