Exploring the link between ultraviolet B radiation and immune function in amphibians: implications for emerging infectious diseases

Rebecca L Cramp,Craig E Franklin

doi:10.1093/conphys/coy035

Abstract

Amphibian populations the world over are under threat of extinction, with as many as 40% of assessed species listed as threatened under IUCN Red List criteria (a significantly higher proportion than other vertebrate group). Amongst the key threats to amphibian species is the emergence of novel infectious diseases, which have been implicated in the catastrophic amphibian population declines and extinctions seen in many parts of the world. The recent emergence of these diseases coincides with increased ambient levels of ultraviolet B radiation (UVBR) due to anthropogenic thinning of the Earth's protective ozone layer, raising questions about potential interactions between UVBR exposure and disease in amphibians. While reasonably well documented in other vertebrate groups (particularly mammals), the immunosuppressive capacity of UVBR and the potential for it to influence disease outcomes has been largely overlooked in amphibians. Herein, we review the evidence for UVBR-associated immune system disruption in amphibians and identify a number of direct and indirect pathways through which UVBR may influence immune function and disease susceptibility in amphibians. By exploring the physiological mechanisms through which UVBR may affect host immune function, we demonstrate how ambient UVBR could increase amphibian susceptibility to disease. We conclude by discussing the potential implications of elevated UVBR for inter and intraspecific differences in disease dynamics and discuss how future research in this field may be directed to improve our understanding of the role that UVBR plays in amphibian immune function.

Highlights

Amphibians are currently the vertebrate taxon most threatened with extinction (Houlahan et al, 2000; Hof et al, 2011; International Union for the Conservation of Nature (IUCN), 2016)
We have found that juvenile frogs, exposed to elevated ultraviolet B radiation (UVBR) as larvae, have reduced antigen responses, reduced white blood cell counts (Ceccato et al, 2016) and are more susceptible to Batrachochytrium dendrobatidis (Bd) than those exposed to low/no UVBR as larvae
We have explored the potential for one changing environmental variable, UVBR, to influence amphibian fitness through its capacity to exert direct and indirect effects on immune function

Summary

Introduction

Amphibians are currently the vertebrate taxon most threatened with extinction (Houlahan et al, 2000; Hof et al, 2011; IUCN, 2016). The impacts of UVBR exposure on amphibian immune function and disease susceptibility have been little studied since, and much remains unknown about whether changes in global UVBR levels have contributed to recent disease-associated amphibian declines.

Results

Conclusion