FROG DECLINES: EXPLORING CONNECTIONS AMONG CLIMATE CHANGE, IMMUNITY AND DISEASE

Abstract

Frog and toad populations have been declining drastically all over the world. For the past 20 years, marked declines have been recorded for 40% of the frog and toad species in the Monteverde Cloud Forest Preserve (MCFP), Costa Rica, where climate change and disease have been implicated. Our study explored possible connections between climate change, immunity and disease susceptibility, examining in particular how climate-induced changes in pond water levels may influence amphibian immune systems. We examined immune development and function (thymus growth, antibody production and skin graft rejection) in Meadow treefrogs (Hyla pseudopuma), a declining species in the MCFP, when tadpoles developed under various water regimes. During the wet seasons of 2001-2004, laboratory experiments were conducted in the MCFP by subjecting tadpoles to constant or declining water levels. Field studies also took place in man-made and natural forest ponds that experienced different rainfall and pond water retention patterns. Our studies suggested that development under shallow or highly variable water levels led to weaker immunity. Under these conditions, both tadpoles and young froglets were less able to reject foreign tissue, an important immune response involved in initially fighting off infection. These data support the hypothesis that climate-induced changes in pond water can influence amphibian immune development as well as function. Collectively, these results may have important implications concerning climate change effects on amphibian populations, as well as the possible role of immunosuppression and increased disease susceptibility in species declines.