Meeting Abstract

38.5  Tuesday, Jan. 5  Relationship between corticosterone, immune response, and parasite load in two species of tropical anurans (Chaunus marinus and Agalychnis callidryas). MENDONCA, M.T*; PATTERSON, S.T.; Auburn University mendonca@auburn.edu

There is little information on patterns of stress responsiveness and immunocompetence in amphibians in general and in tropical species of amphibians in particular. We explored the relationship between these two physiological parameters in two species, the cane toad, Chaunus marinus, and the red-eyed tree frog, Agalychnis callidryas, from La Selva, Costa Rica and related them to parasite load as well as sex and body condition. We bled wild individuals within 3 min of capture to establish baseline levels of corticosterone, complement activity (measured with a functional bacterial lysis assay), and blood leukocyte numbers as well to quantify blood parasite loads (the first two measures from plasma, the last two from whole blood smears). We then restrained these individuals in bags for 60 min, rebled them, and then measured changes in leukocyte profiles, bactericidal activity, and corticosterone. We found that, in the initial sample, cane toads had significantly more blood parasites and higher eosinophil numbers than red-eyed tree frogs though neutrophil/lymphocyte ratio did not differ significantly between the two species. There was a significant difference (p=0.01) between the species in bactericidal ability, with cane toads showing a higher ability to respond to a standard bacterial challenge (i.e. 60% vs. 38.1%). However, this low bactericidal activity in the red-eyed tree frogs was due to a significant sexual dimorphism in response: males exhibited much lower competence than females (28% vs 70%; p=0.004). There was no sexual dimorphism in bactericidal ability in cane toads. Corticosterone levels increased between the 0 and 60 minute sample period but the change was not significant in either species. Further relationships among corticosterone, blood profiles and bactericidal activity time courses will be discussed.