Attachment ofNematospiroides dubius in the murine intestine

Villus length influences habitat selection by Heligmosomoides polygyrus

Heligmosomoides polygyrus is a gastrointestinal nematode whose adult distribution is restricted to the duodenal region in the small intestine of the mouse. This study tests the hypothesis that the habitat of these parasitic worms is influenced by fixed (architectural) cues in the small intestine of the vertebrate host, and that H. polygyrus adults will select microhabitats containing the longest villi. H polygyrus adults attach by coiling around the villi, and longer villi may provide greater attachment resources. In addition, these parasites feed on the epithelial cells covering the villi and thus, longer villi may also provide more food resources. Using histological methods, this study identified a gradient of villus length in the small intestine of the mouse where the longest villi were found in the duodenum and shortest in the ileum. Several non-surgical and surgical treatments were used to differentially alter the overall lengths of the villi. These treatments produced a significant negative correlation between villus length and worm distribution, with the worms selecting regions with the relatively longest villi in the small intestine. Attachment and feeding sites are crucial resources for this parasite, and these data suggest that villus length may be a reliable indicator of resource quality, and that decisions on habitat suitability by H. polygyrus adults may depend on this single, topological variable.

Critical resources that influence habitat selection decisions by gastrointestinal helminth parasites

Habitat selection may be the basis of some of the most exciting questions in behavioural ecology today, but parasites are being excluded from this debate. Parasites are not aberrant; they form a large proportion of the diversity of life on earth, and one estimate suggests that parasitism is more common than all other feeding strategies combined. We still do not understand the adaptive value of habitat selection behaviours in these organisms, even though the literature is full of examples of parasites migrating and navigating through hosts to their specific habitats. Parasites must make the same decisions that every animal has to make regarding food acquisition, shelter and reproduction. However, we cannot even make reasonable guesses on the habitat selection strategies and critical resources that influence their decision-making. The purpose of this review is to provide examples of experiments and methods of incorporating critical resources into the ecological analyses of habitat selection by gastrointestinal parasites. Information on parasite resources is simply not available for most parasites, and these ideas might stimulate and guide future research. In addition, parasites are ideal models to test theoretical assumptions of habitat selection. Experimental manipulations of parasites are ideal models to test theoretical assumptions of habitat selection. Experimental manipulations of parasite populations are simple, and habitats of endoparasites can be precisely altered by surgical methods. Few tests of habitat selection theory have been attempted in free-living environments because of the difficulty of assessing the correlations between environmental variations and organismal success in real-world situations, but this is not a problem with parasites because their habitats are replicated exactly in each host.