Interspecific Variation in Climbing by Gastropods: Implications for Transmission of Parelaphostrongylus tenuis

Abstract

-Most studies of the gastropod intermediate hosts of the nematode parasite Parelaphostrongylus tenuis used cardboard placed on the ground to collect host specimens. We examined interspecific variation in climbing behavior of seven gastropod species from Algonquin Park, Ontario, to evaluate the potential for sampling bias and its implications (1) for inferences regarding which gastropods may be important in parasite transmission and (2) for estimating parasite prevalence in gastropods. Gastropods were highly variable in the degree to which they climbed and when they did so. Zonitoides arboreus, Anguispira alternata and Deroceras laeve climbed relatively infrequently; Stenotremafraternum and Mesodon sp. were most arboreal. Discus cronkhitei and Succinea ovalis were intermediate; they spent about as much time on the ground as they did climbing. Thus, the latter species are potentially most important as intermediate hosts because they frequent the ground where they can become infected with the parasite, but also climb to where they may be more vulnerable to ingestion by foraging deer and moose. A comparison of gastropod collections was made between studies that used cardboard to sample gastropods and studies where hand-searching was used. It revealed that species from the families Zonitidae and Limacidae comprised the largest fractions of collections using cardboard, consistent with the idea that cardboard samples are biased to terrestrial species. If collections are biased, prevalence levels detected for gastropod hosts of P tenuis may underestimate true levels. Therefore, the degree of arboreality among gastropod intermediate hosts could be important to consider when evaluating the potential for different species to serve as important vectors of transmission of P tenuis.