A Skeletochronological Assessment of Age-Parasitism Relationships in Wood Frogs (Lithobates sylvaticus)

Amphibian parasite communities are often suggested to be dependent on host size. However, age-related differences in parasite exposure and susceptibility could lead to differences in parasitism unaccounted for by host size. To address these hypotheses, we determined the ages of Wood Frogs (Lithobates sylvaticus) using skeletochronology and assessed the relationships of host age and size with helminth infections. Neither age nor size was significantly related to helminth species richness. Total infection intensity increased with female age and generally increased with age and size in males. However, these overall measures may mask more complex dynamics with individual helminth species. Although the intensity of Alaria spp. increased in males initially, both the intensity and prevalence of Alaria spp. ultimately decreased with male age. The prevalence of both Fibricola sp. and Echinoparyphium rubrum increased with female age. The abundance of Fibricola sp. also increased with female age, whereas Fibricola sp. prevalence and intensity increased with male size. Rhabdias bakeri abundance increased with female size, but decreased with female age. These results suggest age and size are both related to some aspects of Wood Frog infection dynamics. We hypothesize that the absence of trematode metacercariae in young female frogs may be a result of delayed maturity because femaleWood Frogs generally avoid water until they are reproductively mature. In contrast, male parasite-specific relationships may be the result of host immune response, host mortality, or parasite mortality. Because males and females were sampled at different times of the season, differences in parasitism based on host sex alone should be interpreted with caution.