Host age, sex, and reproductive seasonality affect nematode parasitism in wild Japanese macaques.
MacIntosh, AJJ, Hernandez AD, Huffman MA
Parasites are characteristically
aggregated within hosts, but identifying the mechanisms underlying such
aggregation can be difficult in wildlife populations. I examined the
influence of host age and sex over an annual cycle on the fecal egg output
(EPG) of nematode parasites infecting wild Japanese macaques (Macaca
fuscata yakui) on Yakushima Island. Five species of nematode were
recorded from 434 fecal samples collected from 50 individuals in an
age-structured group of individually recognizable macaques. All parasites
exhibited aggregated EPG distributions. The age-infection profiles of all
three directly transmitted species (Oesophagostomum aculeatum, Strongyloides
fuelleborni, and Trichuris trichiura) exhibited convex curves,
but concavity better characterized the age-infection curves of the two
trophically transmitted species (Streptopharagus pigmentatus and Gongylonema
pulchrum). There was a male bias in EPG and prevalence of infection
with directly transmitted species, except in the prevalence of O.
aculeatum, and no sex bias in the other parasites. Infection with O.
aculeatum showed a female bias in prevalence among young adults, and
additional interactions with sex and seasonality show higher EPG values in
males during the mating season (fall) but in females during the birth
season (spring). These patterns suggest that an immunosuppressive role by
reproductive hormones may be regulating direct, but not indirect life
cycle parasites. Exposure at an early age may trigger an immune response
that affects all nematodes, but trophically transmitted species appear to
accumulate thereafter. Although it is difficult to discern clear
mechanistic explanations for parasite distributions in wildlife
populations, it is critical to begin examining these patterns in host
species that are increasingly endangered by anthropogenic threats.SEP/30/2010
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