Meeting Abstract

P2.52  Sunday, Jan. 5 15:30   Parasite survival in freeze-tolerant hosts LARSON, DJ*; JOHNSON, PTJ; BARNES, BM; Univ of Alaska Fairbanks; Univ. Colorado-Boulder; Univ of Alaska Fairbanks djlarson@alaska.edu

We examined the overwintering strategies of Ribeiroia ondatrae, an ecologically important parasitic trematode, in the freeze tolerant wood frog (Lithobates [Rana] sylvaticus), and tested the hypothesis that the pattern of freezing affects parasite survival. We exposed 107 wood frog tadpoles from interior Alaska each to 30 R. ondatrae cercariae. Wood frogs were raised to metamorphosis and divided into three groups: control, linearly frozen, or frozen over several freeze-thaw cycles, a pattern associated with higher accumulation of cryoprotectants (glucose) and enhanced cold tolerance in naturally freezing wood frogs. We necropsied 10 frogs from each group prior to freezing and found no significant difference in parasite survival. In unfrozen, control wood frogs (n=22) held for two weeks at 2°C, no reduction in parasite survival occurred. Linearly frozen wood frogs (n=26) were cooled from 2°C to -5°C over 12 hours, nucleated at -1.5°C, and then held for two weeks at -5°C; no parasites survived. Wood frogs experiencing successive cycles of freezing and thawing (n=29) were cooled over 12 hours from 2°C to -5°C, nucleated at -1.5°C, and then warmed over 12 hours to 2°C. We repeated this cycle twice before wood frogs were then held at -5°C for two weeks; 23% of parasites survived in this group. We hypothesize that parasite and host overwinter survival is enhanced in wood frogs that experience successive freeze and thaw cycles, due to the higher concentrations of glucose that accumulate with this pattern of freezing that characterizes natural conditions.