Condition-dependent expression of virulence in a trypanosome infecting bumblebees

By Mark J. F. Brown, R. Loosli, P. Schmid-Hempel. 2000

347 citations recorded by the source corpus.

Parasite virulence affects both the temporal dynamics of host-parasite relationships and the degree to which parasites regulate host populations. If hosts can compensate for parasitism, then parasites may exhibit condition-dependent virulence, with high virulence being seen only when the host is under conditions of stress. Despite their usually low level of virulence, theory suggests that such parasites may still affect host population dynamics. We tested whether a trypanosome intestinal parasite of bumblebees, Crithidia bombi, expresses condition-dependent virulence. Hosts were infected with the parasite and then kept under either favourable or starvation (stressed) conditions. Under favourable conditions the infection caused no mortality, while when hosts were starved the infection increased the host mortality rate by 50%. In addition, we found a parasite-related change in host resource allocation patterns. Infected bees invested relatively more resources into their fat body and less into their reproductive system than did non-infected bees. Whether this reallocation is parasite-driven, to enhance transmission, or a host-response to parasitism, remains unknown.

Subfields: Ecology, Evolution, Behavior and Systematics, Genetics, Insect Science

View Paper: https://www.semanticscholar.org/paper/6e4df15795dc04c63258c501e4dcba47534952bc

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Citations in the corpus

Plight of the bumble bee: Pathogen spillover from commercial to wild populations (2006, background): “For example, C. bombi can reduce the reproductive output of bumble bee colonies by 40% (Brown et al., 2003), and reduce the survival of individual workers by 50% when food is scarce (Brown et al., 2000).”
Socially transmitted gut microbiota protect bumble bees against an intestinal parasite (2011, background): “This theoretical prediction would fit well with the horizontal transmission mode (39), weak effect on host mortality (40), but high reduction in host fecundity (16, 41) of the parasite C.”
Bee declines driven by combined stress from parasites, pesticides, and lack of flowers (2015, background): “For example,Crithidia bombi causes littlemortality inwell-fed bumblebees but becomes virulent in bumblebees with a restricted diet (127).”
Factors affecting parasite prevalence among wild bumblebees (2010, background): “Given that Crithidia is considered to be a relatively benign parasite that only exhibits lethal effects under stressful conditions (Brown et al., 2000), it may not be expected to affect laboratory survival when food is abundant.”
Strong context‐dependent virulence in a host–parasite system: reconciling genetic evidence with theory (2003, background): “bombi was found to exhibit condextdependent virulence in food-stressed workers, increasing their mortality rate by 50% (Brown et al. 2000).”
Effects of parasitic mites and protozoa on the flower constancy and foraging rate of bumble bees (2005, neutral): “buchneri are usually considered relatively benign parasites (Schmid-Hempel 1998), perhaps because they do not appear to affect the survival of host colonies (Husband and Sinha 1970), or affect host fitness only during times of stress (Brown et al. 2000; Brown et al. 2003).”
Life histories and parasite pressure across the major groups of social insects. (2005, background): “The trypanosome Crithidia is a chronic infection that is iteroparous and relatively mild for both the infected workers (Brown et al., 2000) and established colonies (Shykoff and SchmidHempel, 1991), but which severely impedes colony foundation by the queen (Brown et al., 2003).”
Biotic and Abiotic Factors Associated with Colonies Mortalities of Managed Honey Bee (Apis mellifera) (2019, background): “causes less mortality if wild bees have a complete food source [110].”
Does parasitic infection impair the ability of bumblebees to learn flower-handling techniques? (2005, background): “Although C. bombi is considered to be a relatively benign parasite, because infection results in death only when bees are deprived of food (Brown et al. 2000), it none the less elicits a measurable immune response (Brown et al. 2003).”
The role of resources and risks in regulating wild bee populations. (2011, background): “have strong negative effects on colony size and reproduction when infected colonies experience starvation or other stressful conditions (10, 11).”