Sex-biased parasitism is not universal: evidence from rodent–flea associations from three biomes

Abstract

The distribution of parasites among individual hosts is characterised by high variability that is believed to be a result of variations in host traits. To find general patterns of host traits affecting parasite abundance, we studied flea infestation of nine rodent species from three different biomes (temperate zone of central Europe, desert of Middle East and tropics of East Africa). We tested for independent and interactive effects of host sex and body mass on the number of fleas harboured by an individual host while accounting for spatial clustering of host and parasite sampling and temporal variation. We found no consistent patterns of the effect of host sex and body mass on flea abundance either among species within a biome or among biomes. We found evidence for sex-biased flea infestation in just five host species (Apodemus agrarius, Myodes glareolus, Microtus arvalis, Gerbillus andersoni, Mastomys natalensis). In six rodent species, we found an effect of body mass on flea abundance (all species mentioned above and Meriones crassus). This effect was positive in five species and negative in one species (Microtus arvalis). In M. glareolus, G. andersoni, M. natalensis, and M. arvalis, the relationship between body mass and flea abundance was mediated by host sex. This was manifested in steeper change in flea abundance with increasing body mass in male than female individuals (M. glareolus, G. andersoni, M. natalensis), whereas the opposite pattern was found in M. arvalis. Our findings suggest that sex and body mass are common determinants of parasite infestation in mammalian hosts, but neither of them follows universal rules. This implies that the effect of host individual characteristics on mechanisms responsible for flea acquisition may be manifested differently in different host species.

Drivers of Intensity and Prevalence of Flea Parasitism on Small Mammals in East African Savanna Ecosystems

“…This may be due in part to body size differences, with larger males providing a larger food resource, but it has also been attributed to differences in immune function (caused by androgen immune suppression), grooming patterns, movement, and social contact patterns (Perez-Orella and SchulteHostedde, 2005;Krasnov et al, 2012). Yet, many other studies have failed to find sex-biased parasitism, or they have found that sex-biased parasitism varies based on parasite examined (Krasnov Kiffner et al, 2013;Waterman et al, 2013). No evidence of sex-biased parasitism across all flea species was found in this study, even when we included size and sex interaction.…”

“…Many factors have been postulated to affect prevalence and intensity of flea parasitism among and within host species (Krasnov et al, 2002c;Whiteman and Parker, 2004;Krasnov et al, 2005;Kiffner et al, 2013). Most factors fall broadly into 2 categories: host factors and environmental factors.…”

Ectoparasite diversity in the eastern rock sengis (Elephantulus myurus): the effect of seasonality and host sex

“…It is surprising however, that this was not apparent for R. warburtoni/arnoldi as higher R.warburtoni burdens have been recorded during the breeding season (August-March) on male sengis at other localities (Lutermann et al 2012b). However, sex-biased parasitism is far from universal and may vary among parasite species infesting the same host as well as within the same parasite species when infesting different hosts (Scantlebury et al 2010;Kiffner et al 2013). Unexpectedly the abundance of R. distinctus was female-biased and the causes for this are not immediately obvious.…”

“…Sex-specific investment strategies in reproduction may account for gender biases in parasite burdens Kiffner et al 2013). This could be due to differences in body size, behaviour and/or physiology between the sexes (Moore & Wilson 2002;Klein 2004).…”

“…Alternatively, higher levels of the male sex hormone testosterone have been shown to increase susceptibility to ectoparasites such as ticks (Hughes & Randolph 2001), while lowered immune defences during gestation can render female mammals more susceptible to ectoparasites (Christe et al 2000;Lutermann et al 2012b). However, sex-biased parasite burdens are not the rule and the degree of sex-bias may differ between different ectoparasite species parasitizing the same host as well as for the same parasite on different host species (Scantlebury et al 2010;Kiffner et al 2013).…”