The major objective of this dissertation is to understand the interplay between ring-tailed lemurs (Lemur catta) and Verreaux’s sifaka (Propithecus verreauxi) and the parasites they harbor at Beza Mahafaly Special Reserve, Madagascar. From November 2005 to July 2006 behavioral data and fecal samples were collected from collared sifaka and lemurs. A total of 683 hours of behavioral data and 585 fecal samples were analyzed. Focal interval sampling and all-occurrence focal behavioral data collection methods were used. Gastrointestinal and ectoparasites were identified using fecal smears, fecal floatation, and fecal sedimentation protocols. All ectoparasites analyzed were removed via oral grooming bouts and were dislodged by sifaka and lemur toothcombs. Data was collected on lemur and sifaka groups living in a protected parcel of gallery forest and an anthropogenically-disturbed habitat.

Comparisons of sifaka and lemur patterns of parasitism demonstrated differences in the parasite intensity, prevalence, and diversity of the ecto- and endoparasites of each species. Ring-tailed lemurs harbored higher counts and a wider diversity of ectoparasites. Lemurs also harbored a broader diversity of endoparasites. These differences were linked to host behavior. Ring-tailed lemurs groomed more and subsequently harbored more ectoparasites. Behavioral differences between these primates also have consequences for their endoparasites burdens. Ring-tailed lemurs are semi-terrestrial, dietary generalists. Sifaka are arboreal folivores. Lemur terrestriality increases the likelihood of acquiring ground-dwelling parasites and insect consumption is responsible for endoparasites that use invertebrates as intermediate hosts. Sifaka avoid ground-dwelling parasites by spending the majority of their time in the trees and circumvent endoparasites that use invertebrates as intermediate hosts by eating a folivorous diet.

For sifaka, no differences in endoparasite prevalence were found between the sexes, seasons, or habitats. Sifaka females harbored more ectoparasites than males and ectoparasite intensity was higher in the wet season. Lemur ectoparasite intensity was higher in the dry season and for the groups living in the gallery forest. Comparisons of endoparasitism revealed no differences between males and females, and only one endoparasite was more prevalent in the wet season. Groups inhabiting the gallery forest groups exhibited a higher prevalence for the worm, Lemuricola bauchoti and a lower prevalence of coccidians.