Condition-dependent expression of virulence in a trypanosome infecting bumblebees

• Published in: Oikos Vol. 91; no. 3; pp. 421 - 427
• Main Authors: Brown, M. J. F., Loosli, R., Schmid-Hempel, P.
• Format: Journal Article
• Language: English
• Published: Copenhagen Munksgaard International Publishers 01.12.2000; Munksgaard International Publishers, Ltd; Blackwell
• Subjects: Animal and plant ecology; Animal protozoal diseases; Animal, plant and microbial ecology; Animals; Autoecology; Biological and medical sciences; Bombinae; BOMBUS TERRESTRIS; Bumblebees; CRITHIDIA; Crithidia bombi; ESTRES; Fundamental and applied biological sciences. Psychology; Infections; Infectious diseases; Insect colonies; Insect reproduction; Medical sciences; Mortality; Ovarioles; PARASITE; Parasite hosts; PARASITES; Parasitic diseases; Parasitism; PARASITOS; Protozoa. Invertebrata; Protozoal diseases; STRESS; SUISSE; SUIZA; SWITZERLAND; Virulence; Physiological condition; Host parasite relation; Protozoal disease; Insecta; Virulence; Apidae; Environmental factor; Apoidea; Bombus terrestris; Trypanosomiasis; Aculeata; Kinetoplastida; Protozoa; Starvation; Mortality; Parasite; Host; Parasitosis; Social insect; Stress; Infection; Trypanosomatidae; Arthropoda; Parasitism; Hymenoptera; Invertebrata
• ISSN: 0030-1299; 1600-0706
• DOI: 10.1034/j.1600-0706.2000.910302.x

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.