Costs of resistance and infection by a generalist pathogen

Abstract

Pathogen infection is typically costly to hosts, resulting in reduced fitness. However, pathogen exposure may also come at a cost even if the host does not become infected. These fitness reductions, referred to as “resistance costs”, are inducible physiological costs expressed as a result of a trade‐off between resistance to a pathogen and aspects of host fitness (e.g., reproduction). Here, we examine resistance and infection costs of a generalist fungal pathogen (Metschnikowia bicuspidata) capable of infecting a number of host species. Costs were quantified as reductions in host lifespan, total reproduction, and mean clutch size as a function of pathogen exposure (resistance cost) or infection (infection cost). We provide empirical support for infection costs and modest support for resistance costs for five Daphnia host species. Specifically, only one host species examined incurred a significant cost of resistance. This species was the least susceptible to infection, suggesting the possibility that host susceptibility to infection is associated with the detectability and size of resistance cost. Host age at the time of pathogen exposure did not influence the magnitude of resistance or infection cost. Lastly, resistant hosts had fitness values intermediate between unexposed control hosts and infected hosts. Although not statistically significant, this could suggest that pathogen exposure does come at some marginal cost. Taken together, our findings suggest that infection is costly, resistance costs may simply be difficult to detect, and the magnitude of resistance cost may vary among host species as a result of host life history or susceptibility.

A genotypic trade‐off between constitutive resistance to viral infection and host growth rate

“…This differentiates the cost of resistance in this system from cases where resistance costs manifest only after exposure to a pathogen (Dallas et al. ). The importance of demonstrating that this evolutionary trade‐off is underpinned by a genetic, constitutive cost begins to help validate the rich body of theory on the evolution of host resistance to pathogens.…”

“…Costs of resistance are often measured when there is exposure to the pathogen (Dallas et al. )–however, such measures represent activated facultative costs only, and cannot inform us about the costs paid by organisms that never encounter a pathogen. Such facultative costs of immune activation are now well demonstrated (Nordling et al.…”

Temperature and host diet jointly influence the outcome of infection in a Daphnia‐fungal parasite system

“…The yeast M. bicuspidata (Ascomycota: Saccharomycetales) is a generalist parasite infecting several Daphnia species (Dallas, Holtackers, & Drake, 2016;Ebert, 2005). Infections of Daphnia hosts by Metschnikowia are common in nature, typically starting in late summer/early autumn (Wolinska, Seda, Koerner, Smilauer, & Petrusek, 2011) and can reach prevalence up to 60% in some lakes (Cáceres et al, 2006;Penczykowski, Hall, Civitello, & Duffy, 2014).…”

Patterns of avian malaria in tropical and temperate environments: testing the "The enemy release hypothesis"

“…Plasmodium and Haemoproteus infections have negative consequences to host fitness by reducing clutch sizes and nest defense behavior, increasing probability of clutch desertion, reducing hatching and fledging success and weaning nestlings with poorer body condition (Korpimaki et al 1993, Dulfa 1996, Hakkarainen et al 1998, Sanz et al 2004, Andrezj 2005, Marzal et al 2005. They also pose a physiological cost to the host birds (Norte et al 2009, Dallas et al 2016, and may ultimately lead to death (Warner 1968, Cannell et al 2013, Vanstreels et al 2014.…”