Host age modulates parasite infectivity, virulence and reproduction

Abstract

Summary1. Host age is one of the most striking differences among hosts within most populations, but there is very little data on how age-dependent effects impact ecological and evolutionary dynamics of both the host and the parasite. 2. Here, we examined the influence of host age (juveniles, young and old adults) at parasite exposure on host susceptibility, fecundity and survival as well as parasite transmission, using two clones of the water flea Daphnia magna and two clones of its bacterial parasite Pasteuria ramosa. 3. Younger D. magna were more susceptible to infection than older ones, regardless of host or parasite clone. Also, younger-infected D. magna became castrated faster than older hosts, but host and parasite clone effects contributed to this trait as well. Furthermore, the earlyinfected D. magna produced considerably more parasite transmission stages than late-infected ones, while host age at exposure did not affect virulence as it is defined in models (host mortality). 4. When virulence is defined more broadly as the negative effects of infection on host fitness, by integrating the parasitic effects on host fecundity and mortality, then host age at exposure seems to slide along a negative relationship between host and parasite fitness. Thus, the virulence-transmission trade-off differs strongly among age classes, which in turn affects predictions of optimal virulence. 5. Age-dependent effects on host susceptibility, virulence and parasite transmission could pose an important challenge for experimental and theoretical studies of infectious disease dynamics and disease ecology. Our results present a call for a more explicit stage-structured theory for disease, which will incorporate age-dependent epidemiological parameters.

Host age modulates within-host parasite competition

“…11: 20150131 the optimal level of virulence [23]. Izhar & Ben-Ami [9] showed that this relationship is age-specific, because younger hosts produced more transmission stages than older ones even though parasite-induced host mortality (virulence) did not vary with host age. Our study further shows that the genetic composition of parasite strains in young multiply-exposed hosts is different from that in older hosts.…”

Disease spread in age structured populations with maternal age effects

“…Earlier work from our laboratory (Garbutt et al . ) and others (Izhar & Ben‐Ami ; Izhar et al . ) showed that older mothers themselves are more resistant to this pathogen.…”

Gall-forming protistan parasites infect southern bull kelp across the Southern Ocean, with prevalence increasing to the south

“…Pathogen transmission can increase with higher densities and greater connectivity between hosts (Poulin et al 2012, Izhar & Ben-Ami 2015. Durvillaea species in Australia are known to transition from being a relatively rare intertidal element at Tathra (the northern range limit) to a dominant habitatforming species on rocky intertidal platforms in Tasmania (southern part of the species' range) (Millar 2007).…”