Social Information use Shapes the Coevolution of Sociality and Virulence

Abstract

Social contacts can facilitate the spread of both survival-related information and infectious disease, but little is known about how these processes combine to shape host and parasite evolution. Here, we use a theoretical model that captures both transmission processes to investigate how host sociality and parasite virulence (co)evolve. We show how selection for sociality (and in turn, virulence) depends on both the intrinsic costs and benefits of information and disease as well as their relative prevalence in the population. Specifically, greater sociality and lower virulence evolve when the risk of infection is either low or high and information is neither very common nor too rare. Lower sociality and higher virulence evolve when the prevalence patterns are reversed. When disease and information are both at moderate levels, the direction of selection depends on the relative costs and benefits of being infected or informed. We also show that sociality varies inversely with virulence, and that disease may be unable to constrain the evolution of sociality. Together, these findings provide new insights for our understanding of group living and how apparently opposing ecological processes can influence the evolution of sociality and virulence in a range of ways.

Novel pathogen introduction rapidly alters evolved movement strategies, restructuring animal societies

“…food, predators; see e.g. Ashby and Farine 2022). In contrast, social information benefits in our model are emergent outcomes of animal movement and foraging mechanisms.…”

“…Analytical models expect pathogen attributes to rapidly co-evolve to match host population attributes (e.g. sociality and immune resistance) (Bonds et al, 2005; Prado et al, 2009; Ashby and Farine, 2022). Such models treat pathogens — just as they do host animals — in relatively simple, non-mechanistic ways.…”

“…Analytical models suggest that animal sociality evolves to balance the value of social information against the risk of pathogen transmission (Bonds et al, 2005; Prado et al, 2009; Ashby and Farine, 2022). However, these models make a number of simplifying assumptions, including homogeneous populations, and single parameters for sociality (Bonds et al, 2005; Prado et al, 2009; Ashby and Farine, 2022). In reality, sociality is an emergent outcome of spatially heterogenous environmental conditions and often substantial withinpopulation heterogeneity in behaviour (Tanner and Jackson, 2012; Wolf and Weissing, 2012).…”

“…Importantly, when a novel pathogen is first introduced into a population, such as during a spillover event, individuals may have no prior experience of cues that indicate infection (Power and Mitchell, 2004), making fine-tuned adaptive individual or social avoidance responses less likely. If they reduce fitness, novel pathogens spreading through host-host contacts may select against host social behaviour, ultimately selecting against social connectivity itself (Altizer et al, 2003; Cantor et al, 2021 b ; Romano et al, 2021; Poulin and Filion, 2021; Ashby and Farine, 2022). This selective pressure may be modulated by landscape productivity (Hutchings et al, 2006) and the benefits of grouping (Almberg et al, 2015; Ezenwa et al, 2016), especially if these can boost fitness in a way that offsets the cost of infection.…”

“…Analytical models suggest that animal sociality evolves to balance the value of social information against the risk of pathogen transmission (Bonds et al, 2005; Prado et al, 2009; Ashby and Farine, 2022). However, these models make a number of simplifying assumptions, including homogeneous populations, and single parameters for sociality (Bonds et al, 2005; Prado et al, 2009; Ashby and Farine, 2022).…”