Immune responses to fleas in two rodent species differing in natural prevalence of infestation and diversity of flea assemblages

Abstract

We studied in vivo immune response to fleas in two gerbils, Gerbillus dasyurus and Gerbillus andersoni allenbyi, which differed in their natural species richness of flea assemblages and prevalence of infestation. G.dasyurus is parasitized naturally by several flea species, but the prevalence of infestation is low, whereas G. a. allenbyi is parasitized by a single flea species, with high prevalence of infestation. We hypothesized that immunological parameters and the cell-mediated specific immune response to an antigen from an unfamiliar flea species differ between the two gerbil species. Parasitized and control gerbils of both species demonstrated similar, relatively low levels of spontaneous glucose consumption. The same was true for the phytohemagglutinin treatment. Responses to antigen from unfamiliar flea species were higher than both spontaneous glucose consumption and response to phytohemagglutinin in parasitized and control G. a. allenbyi and parasitized G. dasyurus. However, no significant difference in the spontaneous blast transformation index and responses to both phytohemagglutinin and flea antigen was found in control G. dasyurus. The number of white blood cells was significantly lower in control than in parasitized G. dasyurus, whereas no difference in the number of white blood cells was found between control and parasitized G. a. allenbyi. The levels of circulating immune complexes and concentrations of immunoglobulins did not differ between parasitized and control individuals in both species. Phagocytic activity was significantly higher in males than in females of G. a. allenbyi but not of G. dasyurus. In addition, phagocytes of G. dasyurus appeared to be significantly more active than those of G. a. allenbyi.

The effects of mite parasitism on the reproduction and survival of the Taiwan field mice (Apodemus semotus)

“…However, studies on other rodents suggest that host gender may not have a systematic effect on their immune defense (Khokhlova et al 2004;Waterman et al 2014). Therefore, the ecology of A. semotus does not seem to support sex-biased parasitism.…”

“…territoriality, immunocompetence, hormone) and their physiological trade-offs have been shown to vary between breeding and non-breeding seasons (reviewed by Krasnov et al 2005;Martin et al 2008), contributing to seasonal fluctuation in parasitism. Rodent species have been reported to invest less in immune defense if probability and/or intensity of parasite attack is low and vice versa (Khokhlova et al 2004;de Bellocq et al 2006). Consequently, if immune defense is costly for A. semotus, which is a likely scenario considering the consistently high prevalence of mite parasitism they are facing (Khokhlova et al 2004;de Bellocq et al 2006), it would be more advantageous, or it would be only possible, for these mice to breed during periods of low probability and/or intensity of parasitism.…”

Reproductive success in two species of desert fleas: density dependence and host effect

“…Average body mass of an adult M. crassus is about 80·g, whereas that of an adult G. dasyurus is about 22·g. In addition, M. crassus possesses 'pre-invasive' immune responses against fleas and maintains a certain degree of immunological 'readiness' (Khokhlova et al, 2004b), whereas G. dasyurus mounts the immune response against fleas only after being attacked (Khokhlova et al, 2004a). Consequently, we predict that negative relationship between reproductive parameters and density will be manifested in G. dasyurus more so than in M. crassus.…”

“…Both these factors can vary among host species (e.g. Khokhlova et al, 2004a). In addition, host body size also can play a role.…”

Flea infestation does not cause a long-term increase in energy metabolism in Gerbillus nanus

“…This finding allows us to differentiate between two optional strategies M. Kam and others proposed for the response of the immune system to parasite infestation. In the first, hosts possessing an induced immune response elevate their energy metabolism when parasitized, whereas in the second, hosts possessing a constitutive immune response maintain a constantly high level of energy expenditure against parasites, even when parasites are not present (Khokhlova et al, 2004;Hawlena et al, 2006;Tripet et al, 2008). The latter host strategy is more costly in term of energy expenditure but maintains a high level of immunological 'readiness' to defend against flea infestation.…”