UV Radiation - A Source of Cellular and Genetic Stress in Large Whales: What We Know and Where to Go Next
Ultraviolet radiation (UVR) is one of the most damaging natural exogenous factors which exists on our planet, since it can affect many fundamental biological functions of living organisms.7 When unresolved or when excessive, exposure to UVR can lead to erythema,4 skin cancer, immunosuppression and photoaging2. Although the release of ozone-depleting substances was halted in the past decades, the amount of UVR that reaches our earth's surface continues to increase, and will continue to do so until the ozone holes are recovered.1,7 Currently, it is estimated that the annual global stratospheric ozone loss is approximately 3%.6 In this context, investigating the effects that UVR can exert on natural populations is relevant, mainly because of the deleterious effects that have been reported in a number of species3,7 and, particularly, in marine and freshwater ecosystems9. We recently reported that UVR-induced lesions are prevalent in large whales. Blue whales (Balaenoptera musculus), fin whales (Balaenoptera physalus) and sperm whales (Physeter macrocephalus) sampled within the Gulf of California, Mexico, showed clear evidence of epidermal damage associated with acute and severe sunburn.5 Histological abnormalities included intracellular edema, cytoplasmic vacuolization, glycogen deposition, microvesicles and infiltration of leukocytes.5 Pigmentation differences between the three species, and the time remaining on the surface, were the main drivers for quantitative differences in individual skin lesions.5 Those results suggested that sustained exposure to UVR due to thinning of the ozone layer is a significant and plausibly growing threat to the health of large whales. Furthermore, we found evidence of distinct mechanisms to counteract UVR-induced damage, particularly that of overexpression of pigmentation pathways in the blue whale.5 In the context of global environmental change, species will tend to adapt and thus modify their dispersion habits, behavior or physical characteristics, depending on the plasticity of these traits.7 Keeping in mind that plasticity is costly,8 it is relevant to understand the constraints and genetic basis of phenotypic responses to UVR, which may be under selection. Using a sample archive of 235 blue whale skin biopsies and a photocatalogue of 750 blue whales photographed between 1996 and 2012, we will take our previous findings further by quantifying and investigating changes in individual pigmentation at different points in their life and throughout a particular season. State-of-the-art genetic and gene expression technologies will allow us to quantify the amount of photoproducts in whale DNA and quantify the expression of UV-damage repair enzymes. By adding our study to previous findings, our results will help to predict negative effects of global environmental changes on the viability of natural populations.9
*Presenting author
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