Measuring Immune Development in Larval Amphibians to Understand Age-dependent Susceptibility to Infection by Riberoia ondatrae (Class Trematoda)

Riberoia ondatrae, a trematode from the Psilostomatidae family, is one of the major contributors to amphibian malformations. Infection with Riberoia during limb development may result in the amphibian developing deformities such as multiple limbs, skin webbing, missing limbs and total suppression of limb development.  Johnson et al. (2011) found that the age and the stage of development of these amphibian hosts influenced the probability of infection and the resulting infection intensity, both decreasing with amphibian development. A change in the composition of the innate immune system could be a possible explanation for these age dependent malformations. We hypothesize that the variations in the degree of infection and pathology within different stages of development of larval amphibians may be explained by the relative abundance of certain cells of the immune system. To assess this hypothesis we exposed tadpoles of the species Pseudacris triseriata with Riberoia ondatrae cercariae (n=20), extracted from already infected Planorbella snails. We counted different types of blood cells – lymphocytes, neutrophils, eosinophils, basophils, monocytes and erythrocytes- from blood smears collected from tadpoles at different time points of development (stages). Within each stage we will compare controls (n=6 per stage) to Riberoia exposed individuals (n=6 per stage) to examine the immune response to infection. Blood smears are still being counted. In particular, we expect to find increasing numbers of neutrophils and eosinophils in infected individuals in amphibians of later stages.