Differential Parasitism of Native and Introduced Snails: Replacement of a Parasite Fauna

Abstract

The role of parasites in a marine invasion was assessed by first examining regional patterns of trematode parasitism in the introduced Japanese mud snail, Batillaria cumingi (= B. attramentaria), in nearly all of its introduced range along the Pacific Coast of North America. Only one parasite species, which was itself a non-native species, Cercaria batillariae was recovered. Its prevalence ranged from 3 to 86%. Trematode diversity and prevalence in B. cumingi and a native sympatric mud snail, Cerithidea californica, were also compared in Bolinas Lagoon, California. Prevalence of larval trematodes infecting snails as first intermediate hosts was not significantly different (14% in B. cumingi vs 15% in C. californica). However, while the non-native snail was parasitized only by one introduced trematode species, the native snail was parasitized by 10 native trematode species. Furthermore, only the native, C. californica, was infected as a second intermediate host, by Acanthoparyphium spinulosum (78% prevalence). Given the high host specificity of trematodes for first intermediate hosts, in marshes where B. cumingi is competitively excluding C. californica, 10 or more native trematodes will also become locally extinct.

Introduced cryptic species of parasites exhibit different invasion pathways

“…Only one of eight trematode morphospecies, C. batillariae, found in the source region in Japan has invaded North America (21). Interestingly, of the eight cryptic species of this C. batillariae in Japan (20), only three species (HL1, HL6, and HL2) were found in the introduced range (Fig.…”

“…However, its infective propagules were unable to become established until the introduction of its obligate first intermediate host snail, B. attramentaria. Although HL1 may have been transported to North America for a long time, it did not adapt to use the confamilial and sympatric North American mud snail, Cerithidea californica, as an alternative first intermediate host (21). This is not surprising, given that trematodes are typically exceptionally host-specific for their first intermediate host (30,31).…”

“…These trematode species generally use fishes or invertebrates as second intermediate hosts and birds as final hosts. Of these eight morphologically distinct trematode species, only the most common species, Cercaria batillariae (20), has invaded North America with its snail host (21). An interesting caveat is that, within its native range, this single morphologically recognized parasite species is actually a complex of eight genetically distinct cryptic species (morphologically similar but genetically distinct species) (20).…”

Parasite species richness and intensity of interspecific interactions increase with latitude in two wide‐ranging hosts

“…We treated sites as independent samples for our analyses, because these snails have very low mobility, and trematode diversity varies over small spatial scales (Hechinger and Lafferty 2005, Torchin et al 2005, Hechinger et al 2007). We targeted the largest snails from each site for dissections, as these are generally older and have a higher probability of being infected with parasites (e.g., Kuris 1990, Sousa 1993, Torchin et al 2005. Snails were measured from the apex of the spire to the apertural base with Vernier calipers and processed for parasites following Torchin et al (2005).…”

“…We targeted the largest snails from each site for dissections, as these are generally older and have a higher probability of being infected with parasites (e.g., Kuris 1990, Sousa 1993, Torchin et al 2005. Snails were measured from the apex of the spire to the apertural base with Vernier calipers and processed for parasites following Torchin et al (2005). Trematode species were identified following Martin (1972) and R. F. Hechinger and T. C. Huspeni (unpublished manuscript).…”