Aggression is a complex behavior in which harm is intentionally inflicted onto another individual. Most definitions of aggression require competition as the motivation for harm. In contrast, most aggression taxonomies exclude predation because it is proximally motivated by nutrition and not competition. Many neuroscience studies of aggression have focused on aggression between males for mate access, in which the motivation is unquestionably competitive and behavior is typically stereotyped. There have also been a considerable number of studies that have argued for the aggressive nature of predatory attack based on separability of killing and feeding on behavioral and neuroanatomical levels. However, very few studies have attempted to disentangle competitive and predatory motivations in intraguild predation, which is the predation of a potential competitor. The intraguild predator and intraguild prey exploit the same resource. When the intraguild predator kills the intraguild prey, it simultaneously achieves nutritional and competitive benefits, whether or not interference competition was intended. Unlike in male-male aggression, there are no obvious behavioral clues about the degree to which competition motivates intraguild predation. The aim of this dissertation is to devise a strategy for dissecting the nebulous motivations of intraguild predation and identify neural signaling principles for flexibly switching between competitive and predatory motivations. To achieve this aim, I used the facultative predatory nematode
Pristionchus pacificus as the intraguild predator, Caenorhabditis elegans as the intraguild prey, and bacteria as the shared resource.
In Chapter 1, I review key literature that establish the foundational principles that inspire this work and introduce the tripartite members of the intraguild predation model studied in Chapter 2.
In Chapter 2, I articulate behavioral models of predatory and competitive motivations of P. pacificus biting that I used to determine that intraguild predation is primarily motivated by competition with C. elegans for a limited bacterial resource when P. pacificus is well-fed. I then describe a model of how D2-like and octopamine receptor signaling communicate bacterial information to influence biting across various food and hunger contexts.
In Chapter 3, I discuss further conclusions and future directions.