Interspecific and intraspecific variation in cercariae release.

Given the importance of temperature for the shedding of trematode infective stages (cercariae) from gastropod first intermediate hosts, we investigated the response to temperature increases of trematodes of the intertidal snail Zeacumantus subcarinatus collected from different latitudes (differing in mean annual summer temperature) on the South Island of New Zealand. We investigated whether shedding of cercariae at elevated temperatures differed both between species (interspecific variation) and among populations of each trematode species (intraspecific variation). The shedding of one trematode species, Maritrema novaezealandensis (Microphallidae), appears to decrease with increased temperature and differed among locations. In contrast, the shedding of a second species, Acanthoparyphium sp. (Echinostomatidae), increased at warmer temperatures. In particular, Acanthoparyphium sp.-infected snails from 1 location showed the greatest increase in the shedding of cercariae in response to elevated temperature. Our results demonstrate that different trematode species and populations may be dissimilarly impacted by temperature changes resulting from global warming. In addition, both interspecific and intraspecific variation may result in different impacts of trematodes on ecosystems at different locales.