The evolutionary ecology of sibling cannibalism in the wild

Abstract

Sibling cannibalism is common amongst animals. Whilst the role relatedness plays in this behaviour has been well studied due to the strong ties between cannibalism and evolutionary theory, we lack enough knowledge of the ecology underlying this behaviour to properly explain its evolution. In this thesis I explore the evolutionary ecology of sibling cannibalism, placing emphasis on integrating ecology into tests of cannibalism and the role of Hamilton’s Rule. I explore inter- and intraspecific variation in cannibalism in four species of lygaeid seed bug in the laboratory, showing that developmental stage is a crucial determinant of cannibalism levels within this group, with cannibalism also being shaped by prior experience of conspecifics in Spilostethus pandurus. Field studies of cannibalism are rare but important if we are to properly understand the ecology of this behaviour. I therefore examine the predictions of Hamilton’s Rule in hatchlings of the seed bugs Lygaeus creticus and S. pandurus in both the laboratory and the field. The predictions of Hamilton’s Rule were able to explain the lack of kin avoidance, with cannibalism providing a major survival benefit.
Furthermore, I found that the preference shown by L. creticus for conspecific eggs (over heterospecific S. pandurus eggs) was flexible and shaped by post-hatching experience. Whilst patterns of cannibalism were generally similar across the laboratory and field, the unusual preference for kin and reduced consumption of heterospecific L. creticus eggs shown by S. pandurus in the laboratory suggest evolved responses due to the differing ecologies of lab rearing and life in the wild. Considering ecology alongside evolutionary theory provides important contextualisation, improving our understanding of the evolution of sibling cannibalism. As such, the study of sibling cannibalism provides opportunities for more detailed tests of evolutionary theory in behavioural ecology.

Date of Award	2 Dec 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	David Shuker (Supervisor) & Matthew Tinsley (Supervisor)