Filial Cannibalism in a Fish with Paternal Care

Abstract

Filial cannibalism – the consumption of one’s own offspring – has been described in a wide range of animal taxa, while being particularly common in fish showing paternal care. Despite being a well-known phenomenon, this seemingly odd behaviour has puzzled researchers for decades and its adaptiveness is still not fully understood. Previous research on this topic has mainly focussed on the hypothesis that parents may consume their offspring to satisfy their own energetic needs, but the available evidence indicates that there is more to filial cannibalism than energetics alone. During the course of this thesis, I investigated several alternative hypotheses on the adaptiveness of filial cannibalism. For this, I conducted a series of extensive laboratory experiments using a small marine fish, the common goby (Pomatoschistus microps), as a model species. By simultaneously presenting egg-guarding male common gobies with eggs of varying age, I was able to show that the young, least valuable eggs are preferentially cannibalised (chapter I). This confirms the prediction that filial cannibalism may be a mechanisms to selectively remove and consume offspring with a certain “low-quality” phenotype. Similarly, I could demonstrate that egg infections, but not paternity, trigger such selective filial cannibalism (chapter II). Using a different approach, I tested how water salinity, egg density and their interaction relate to cannibalistic behaviour (chapter III). I could show that filial cannibalism is increased in low salinity as predicted due to increased growth of egg pathogens under such conditions, while this was not the case for the presumably similarly susceptible high-density egg clutches (chapter III). By investigating these different yet connected factors, I could demonstrate in this thesis that filial cannibalism is indeed likely influenced by a wide array of environmental, parental and offspring parameters, while highlighting egg infections as a major driver at least in fish.