Abstract

We studied the growth and survival of wood frog, Rana sylvatica, larvae infected with the leech, Desserobdella picta, a common ectoparasite of amphibian larvae and adults. In a laboratory setting, we exposed wood frog tadpoles of different body sizes and environmental rearing conditions to 0–5 leeches to determine their direct and interactive effects on tadpole growth and survival. Increased parasite intensity was positively correlated with leech pathogenicity for all experimental conditions and resulted in dramatically lower larval growth rates and survival. Leech infection also contributed to significant interactions involving tadpole body size, rearing temperature, food level and population density. Leeches had a disproportionately greater effect on small tadpoles and tadpoles reared at lower temperatures, lower food levels, and higher population densities. This was particularly true for tadpoles infected by a single leech; tadpoles infected by two or more leeches all died shortly after being infected regardless of body size or environmental rearing conditions. Our results also demonstrated that tadpoles were more likely to be infected by a single leech, even at high leech densities, indicating that interactive effects are likely to be important regardless of leech population size. Collectively, our results demonstrate that leeches have significant lethal and nonlethal effects on tadpole fitness traits. However, the magnitude of their impact on wood frog survival and population growth will depend on environmental factors and to a lesser degree on leech abundance.