Divergent water requirements partition exposure risk to parasites in wild equids. Issue 3 (14th March 2022)

• Record Type: Journal Article
• Authors: Tombak, Kaia J.; Easterling, Laurel A.; Martinez, Lindsay; Seng, Monica S.; Wait, Liana F.; Rubenstein, Daniel I.
• Is Part Of: Ecology and evolution. Volume 12:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-14
• Subjects: equid parasitology -- fecal egg counts -- gastrointestinal nematodes -- helminth transmission risk -- Parasite exposure risk -- zebra habitat use; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.8693
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: For grazing herbivores, dung density in feeding areas is an important determinant of exposure risk to fecal‐orally transmitted parasites. When host species share the same parasite species, a nonrandom distribution of their cumulative dung density and/or nonrandom ranging and feeding behavior may skew exposure risk and the relative selection pressure parasites impose on each host. The arid‐adapted Grevy's zebra ( Equus grevyi ) can range more widely than the water‐dependent plains zebra ( Equus quagga ), with which it shares the same species of gastrointestinal nematodes. We studied how the spatial distribution of zebra dung relates to ranging and feeding behavior to assess parasite exposure risk in Grevy's and plains zebras at a site inhabited by both zebra species. We found that zebra dung density declined with distance from water, Grevy's zebra home ranges (excluding those of territorial males) were farther from water than those of plains zebras, and plains zebra grazing areas had higher dung density than random points while Grevy's zebra grazing areas did not, suggesting a greater exposure risk in plains zebras associated with their water dependence. Fecal egg counts increased with home range proximity to water for both species, but the response was stronger in plains zebras, indicating that this host species may be particularly vulnerable to the elevated exposure risk close to water. We further ran experiments on microclimatic effects on dung infectivity and showed that fewer nematode eggs embryonated in dung in the sun than in the shade. However, only 5% of the zebra dung on the landscape was in shade, indicating that the microclimatic effects of shade on the density of infective larvae is not a major influence on exposure risk dynamics. Ranging constraints based on water requirements appear to be key mediators of nematode parasite exposure in free‐ranging equids. Abstract : Exposure risk to fecal‐orally transmitted parasites depends on the spatial distribution of feces and of feeding behavior and can be compounded when multiple sympatric host species share the same parasites. We present evidence that in equid hosts, water dependence is a key determinant of exposure risk to gastrointestinal nematodes because dung density increases with proximity to water access points. Our results indicate that the water‐dependent plains zebra has higher exposure risk than the arid‐adapted Grevy's zebra to shared parasites on a common landscape, skewing the burden of parasite pressure between these hosts with implications for coexistence and habitat suitability.