https://link.springer.com/article/10.1007%2Fs00442-005-0345-4
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Abstract
Host age is one of the key factors in host–parasite relationships as it possibly affects infestation levels, parasite-induced mortality of a host, and parasite distribution among host individuals. We tested two alternative hypotheses about infestation pattern and survival under parasitism in relation to host age. The first hypothesis assumes that parasites are recruited faster than they die and, thus, suggests that adult hosts will show higher infestation levels than juveniles because the former have more time to accumulate parasites. The second hypothesis assumes that parasites die faster than they are recruited and, thus, suggests that adults will show lower infestation levels because of acquired immune response and/or the mortality of heavily infested juveniles and, thus, selection for less infested adults. As the negative effects of parasites on host are often intensity-dependent, we expected that the age-related differences in infestation may be translated to lower or higher survival under parasitism of adults, in the cases of the first and the second hypotheses, respectively. We manipulated ectoparasite numbers using insecticide and assessed the infestation pattern in adult and juvenile gerbils (Gerbillus andersoni) in the Negev Desert. We found only a partial support for age-dependent parasitism. No age-related differences in infestation and distribution among host individuals were found after adjusting the ectoparasite numbers to the host’s surface area. However, age-related differences in survival under parasitism were revealed. The survival probability of parasitized juveniles decreased in about 48% compared to unparasitized hosts while the survival probability of adults was not affected by ectoparasites. Our results suggest that the effect of host age on host–parasite dynamics may not explicitly be determined by age-dependent differences in ectoparasite recruitment or mortality processes but may also be affected by other host-related and parasite-related traits.
Alternatively, it is possible that theprocesses of ectoparasite recruitment and ectoparasite mortality depend on hostage but operate in opposite directions and, thus, the two processes cancel eachother (Anderson and Gordon 1982). For example, the tendency of adult wood mice (Apodemussylvaticus) to accumulate more nematodes Heligmosomoides polygyrusthan juvenile wood mice counter the better ability of adults to mount an immuneresponse (Quinnell 1992). Furthermore, the processes of ectoparasiterecruitment and ectoparasite mortality may be influenced by factors other thanthe level of host exposure, immune response, and parasite-induced hostmortality. For instance, in a larger-scale survey, it was shown that age-biasedflea parasitism might change from juvenile-biased toward adult-biased as afunction of soil temperature and ED (Hawlena et al. 2005).
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发表于 2019-8-29 18:08:28
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