Host Cognition and Parasitism in Birds: A Review of the Main Mechanisms

Abstract

Parasites can have important detrimental effects on host fitness, thereby influencing their ecology and evolution. Hosts can, in turn, exert strong selective pressures on their parasites, affecting eco-evolutionary dynamics. Although the reciprocal pressures that hosts and parasites exert on each other have long been recognized, the mechanisms are insufficiently understood. Here, we discuss the role of host cognition in host-parasite eco-evolutionary dynamics. Theoretical advances have acknowledged the importance of behavior in shaping these dynamics, but how and why host cognition should affect and/or be affected by parasites is less clear. We propose three scenarios that may create causal and non-causal links between cognition and the richness, prevalence and intensity of parasites. First, host cognition may change the probability of exposure to parasites, either increasing (e.g., altering the relationship with the environment via innovative behaviors) or decreasing (e.g., influencing decision-making to avoid infected conspecifics) exposure. Second, parasites may change host cognitive performance, for example, by reducing host condition. Finally, host cognition and parasites can be associated via common causal factors (e.g., shared molecular pathways), energetic constraints generating trade-offs between cognition and immunocompetence, or trait co-evolution with life history, ecological, or social strategies. The existence of such a variety of non-mutually exclusive mechanisms suggests that host cognition has a great potential to affect and be affected by parasites. However, it also implies that progress in understanding these effects will only be possible if we distinguish between causal and non-causal links.

The Role of Cognition in Social Information Use for Breeding Site Selection: Experimental Evidence in a Wild Passerine Population

“…variance in learning performance, we found no relation between learning score and the probability to copy tit preference in males, whether yearling or older. These results suggest that cognitive abilities (in this study learning ability) can at least partly shape information use for decision-making, here in females, providing a new mechanistic explanation for the positive link between cognitive abilities and fitness components (Cauchard et al, 2017; see also Ducatez et al, 2020) that was previously observed in the wild (e.g., Keagy et al, 2011;Cauchard et al, 2013;Smith et al, 2015).…”

Linking ecology and cognition: does ecological specialisation predict cognitive test performance?

“…Moreover, birds and Old World primates exposed to seasonal changes in food availability tend to have larger brains than species living in non-seasonal habitats (van Woerden et al 2012;Sayol et al 2016). Innovativeness, which is adaptive in variable environmental conditions, correlates positively with brain size in primates and birds (Reader and Laland 2002;Lefebvre et al 2004;Overington et al 2009), but it also correlates positively with parasitism and immunocompetence in birds (Møller et al 2005;Garamszegi et al 2007;Vas et al 2011), though the link between innovation and the transmission mode of parasite types is not obvious (Ducatez et al 2020a). Finally, in line with the EIH, brain size was best predicted by diet or home range size in primates (DeCasien et al 2017;Powell et al 2017).…”

Animal Cognition in an Urbanised World

“…Secondly, the prevalence and diversity of parasites may differ between urban and rural habitats, with potential implications for cognitive performance. A recent review by Ducatez et al (2020a) outlines the potential feedbacks between parasitism and host cognition: through its effects on behaviour, cognition may increase or decrease an individual's exposure to parasites (e.g., the exploitation of novel food sources may expose hosts to new parasites; hosts may develop innovative behaviours that reduce parasite load), and parasite infection may have a direct influence on host cognitive performance. However, evidence to date remains largely correlative, and studies have yet to demonstrate a direct role for cognition in influencing host exposure or susceptibility to parasites.…”

“…between cognition and parasitism may be mediated by other traits such as sociality, life history and immunocompetence. Distinguishing between these causal and non-causal links will be necessary to fully understand the interactions between parasites and cognition (Ducatez et al, 2020a).…”