A parasite that increases host lifespan

Abstract

Tenebrio molitor is an intermediate host for the rat tapeworm, Hymenolepis diminuta. Parasite oncospheres hatch in the beetle midgut and burrow through into the haemocoel, where they rapidly grow and mature into metacestodes. Repair of damage incurred during invasion and the nutritional demands of the parasites are likely to impose costs on the host. Despite these costs, there is an overall very highly significant difference in survival time (p < 0.001) between infected and control populations of beetles, with a hazard ratio of 2.35 (control versus infected). Infected females showed a 40% increase in survival time to 50% mortality and males showed a 25% increase in survival time to 50% mortality. This parasite-induced increase in host longevity is discussed in the light of changes in resource allocation that may occur in infected beetles. Previous findings have demonstrated that reproductive success is significantly reduced in infected females. The outcome of changes in the reproductive effort made by male beetles is less clear. We suggest that the optimum trade-off between reproduction and longevity may be altered to favour longer host survivorship, which is likely to enhance parasite transmission.

The parasite's long arm: a tapeworm parasite induces behavioural changes in uninfected group members of its social host

“…Interestingly, two studies support the suggestion that parasites can be responsible for the increased survival of their intermediate hosts. For instance, survival of female beetles increased upon infection with the rat tapeworm Hymenolepis diminuta [40]. Moreover, a recent transcriptome study on the T. nylanderi-A.…”

The energetic budget ofAnopheles stephensiinfected withPlasmodium chabaudi: is energy depletion a mechanism for virulence?

“…Shifts in resource allocation in response to parasite infection are well documented, although they are often inferred from shifts in life-history traits, such as fecundity and longevity (Sorensen & Minchella 1998;Hurd 1998Hurd , 2001Hurd et al 2001), and are only rarely measured directly (Kearns et al 1994;Brown et al 2000). In our experiment, we tested for nutrient reallocation by measuring the levels of other resources in the body that are known to produce glucose as a result of their catabolism: glycogen and protein (Nijhout 1994;Clements 1999).…”

How much energy should manipulative parasites leave to their hosts to ensure altered behaviours?

“…Complete or partial castration induced by trophically transmitted parasites in an intermediate host could also have evolved in this context; because of the trade-off between reproduction and longevity, the energy saved could be used by the host to fuel manipulative changes (e.g. the host lifespan) (Hurd et al, 2001). The HERC hypothesis also provides a possible explanation for the important intraspecific variability observed in host manipulation in nature as the intensity of the manipulation could be related to the host condition.…”