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Research: Do parasites cause harm?

By definition parasites cause harm to their hosts, whereas hosts defend themselves
parasites. Studies of physiological responses of hosts to ectoparasites,
however, often fail to find a cost. Parasites are distributed unevenly among different host species. The host species that supports the majority of parasite individuals is considered the principal host for that parasite, while other hosts are considered auxiliary hosts.  The principal host undergoes stronger selection than auxiliary hosts to evolve adaptations that mediate the costs of parasites; thus, the strength and type of physiological response of a host to a parasite, and the harm caused by the parasite, should differ between principal and auxiliary hosts. 

Ecological Associations: To investigate how the strength of the ecological relationship between a host and a parasite affect the behavioral and physiological responses of the host to infection by the parasite, we are measuring resting metabolic rate and quantifying grooming behavior in different combinations of hosts and parasites.  We predict that energy expenditure will be lower in host-flea combination with the primary host than in host-flea combinations with the auxiliary host.

Environmental Conditions:
  Many small desert mammals live in burrows to escape harsh desert conditions, but CO2 can build up in the burrow and inspiring high CO2 can suppress immune function. Thus, we hypothesized that high CO2 would increase ectoparasite loads.  To test this hypothesis we combine techniques from immunology, from host-parasite studies, and from comparative physiology to ask ecologically relevant questions about how mammals deal with environmental stressors. I found that high CO2 reduced reproduction and survival of fleas without altering immune function or energetics of the host, Sundevall’s jirds (Meriones crassus). Thus high CO2 in burrows may actually help reduce parasite loads.

Host State: We are also investigating how host state (e.g., reproductive condition) affect host-parasite interactions. Levels of reproductive and stress hormones change during pregnancy and lactation, as does energy expenditure.  We are investigating how these changes in physiological measures of the host affect flea fitness and how the flea infestations affect these physiological measures. 

These projects are all ongoing collaborations begun during my tenure as the Blaustein Postdoctoral Fellow at Ben-Gurion University of the Negev. 

With Boris Krasnov, Irina Khokhlova, Berry Pinshow, and Elizabeth Delugosz at Ben-Gurion University of the Negev