Cold hardiness in two helminth parasites of the freeze-tolerant wood frog, Rana sylvatica

D. C. Woodhams, J. P. Costanzo, J. D. Kelty, Jr Lee

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10 Scopus citations


Wood frogs, Rana sylvatica, tolerate the freezing of their body tissues as an overwintering adaptation. Various parasites infect wood frogs of northern populations, but nothing is known about their strategies for surviving within a frozen host. We examined winter-conditioned wood frogs that were experimentally exposed to 0°C (nonfrozen) or -4°C (frozen) to determine whether endoparasites survive the freezing of their host. We found no differences in the prevalence or intensity of adult lungworms Rhabdias ranae (Nematoda) or of larvae of an unidentified species of digenetic trematode between these groups. Live individuals of both species were observed in hosts that recovered from experimental freezing at -4°C. Within the host, R. ranae also tolerated exposure to -5°C, a temperature near the lower limit of survival of the wood frog. Cryostage experiments showed that, like its host, R, ranae was highly susceptible to inoculative freezing and tolerant of the freezing of its tissues. Rhabdias ranae frozen in vitro in the presence or absence of 250 mM glucose, the cryoprotectant used by wood frogs, recovered from a 10-h exposure to -4°C. The mechanism of cold tolerance used by larval trematodes was not investigated; however, we hypothesize that freeze avoidance by supercooling may be important in this species. Freeze-tolerant anurans, such as the wood frog, are useful subjects in the study of coevolution of thermal tolerance in parasites and their host.

Original languageEnglish
Pages (from-to)1085-1091
Number of pages7
JournalCanadian Journal of Zoology
Issue number6
StatePublished - 2000


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