Helminth Parasitism in Isloated Populations of a Neotropical Forest Rodent
File(s)
Date
2012-05Author
Ireland, Annette L.
Advisor(s)
Adler, Gregory
Metadata
Show full item recordAbstract
Parasitism is an extremely common life style that has evolved independently
many times, and parasites are diverse with respect to that life style. Parasitic nematodes
are commonly found in rodents and can serve as excellent model systems for
understanding parasite-host interactions. Proechimys semispinosus (the Central
American spiny rat) is a widely-distributed and common rodent in Neotropical forests.
Several species of intestinal nematodes have been isolated from this rat, including
Heligmostrongylus sp. I analyzed data collected from isolated populations of P.
semispinosus. The data set included counts of eggs of Heligmostrongylus sp. that were
shed in the feces of their rat hosts. The data were collected over a 13-month period
(January 1997 through January 1998) from rat populations on seven small islands in
Gatun Lake, central Panama. Rats were censused monthly by live trapping, and monthly
fruit availability was assessed by counting the numbers of trees and lianas that were
producing ripe fruits. Rat populations on five islands were provisioned with
supplemental food during the period of least food availability (November and December
1997 and January 1998) to test the effects of host nutritional status on reproductive
activity of Heligmostrongylus sp. Rat fecal samples were collected from each captured
individual, and nematode eggs were counted from each sample. I estimated monthly rat
densities, fruit densities, and per capita fruit availability for each island. I also calculated
three indices (egg density, prevalence, and egg density of egg-shedding individuals ) of
Heligmostrongylus sp. reproductive activity. Egg density and density of egg-shedding
individuals were log10+1-transformed, and prevalence was arcsine square roottransformed.
I computed cross-correlation functions of each pair-wise island
combination to search for synchrony in nematode reproductive activity among insular
populations of rats. I computed Spearman rank correlation coefficients of island-wide
means of the three Heligmostrongylus sp. indices and rat density, fruit density, and per
capita fruit availability. I used repeated measures analysis of variance (ANOVA) to
search for differences in mean parasite indices with respect to treatment period, treatment
group, population nested within treatment group, month, and the month x treatment group
interaction. I then searched for differences in the mean number of eggs shed by rats
according to age and sex by constructing a full ANOVA model that included age, sex,
and the interaction. I compared the proportions of male and female rats that shed
nematode eggs at some time in their capture histories. I used linear regression analysis to
search for a relationship between the number of eggs shed and rat body weight.
Reproductive activity of Heligmostrongylus sp. varied widely over time, but there was
little evidence of synchrony among islands. There were no associations of the parasite
indices with rat density, fruit density, or per capita fruit availability. Food provisioning
had no effect on reproductive activity, but such activity varied among islands. There
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were no differences in Heligmostrongylus sp. reproductive activity between age classes
of rats, but female rats shed more eggs than did males. By contrast, the proportions of
male and female rats shedding eggs did not differ, and there was no relationship between
the number of eggs shed by a rat and it body weight. Results suggest that reproductive
activity of Heligmostrongylus sp.is infrequent and aseasonal but spatially variable. Host
nutritional status has little effect on nematode reproductive activity, but dietary or
physiological consequences of female rat reproduction may increase nematode activity. I
suggest that Heligmostrongylus sp. has little impact on host fitness or population-level
processes.
Subject
Rodent population - Panama
Proechimys
Parasites
Parasitism
Helminth
Permanent Link
http://digital.library.wisc.edu/1793/62201Description
A Thesis Submitted In Partial Fulfillment of the Requirements For the Degree of Master of Science - Biology