The role of natural sunscreens for the control of ultraviolet radiation damage in reef fish

A project undertaken at the University of Queensland and supervised by Dr. Ulrike Siebeck, School of Biomedical Science, Sensory Neurobiology Group and Maxi Eckes (PhD Candidate), School of Biological Science.

Research Focus

UV radiation (UV) is something we associate with negative effects, such as skin cancer and DNA damage caused by a part of sunlight we cannot see (Gallagher & Lee, 2006) and we are reminded daily to protect ourselves with sunscreens, sunglasses and hats. Fur and feathers protect the skin of many animals, and UV-absorbing compounds are often found in animal eyes to protect their sensitive visual tissues (Siebeck & Marshall, 2000). Incredibly, however, instead of protecting their eyes from UV radiation, there are animals, including some birds and many coral reef fish that are using this waveband for communication (Bennett, 1994; Siebeck, 2004). How do these animals cope with the negative effects of UV radiation? What is of great concern currently is that UV levels have been rising and will continue to rise, as part of climate change (Zepp et al., 2007). This rise is predicted to be particularly acute for aquatic animals as the transparency of water to UV radiation is increasing (Schindler et al., 1996; Hoegh-Guldberg et al., 2008). Already we are seeing the decline of aquatic species, such as amphibians, which has been largely attributed to the rising UV levels (Häder et al., 2007). How will potentially vulnerable animals deal with an increase in UV radiation, including those that rely on UV signalling for communication? 

Key Aims

1. To assess the role of fish sunscreens (MAAs) for the control/prevention of UV-induced DNA damage.
2. To assess the role of UV colours in the control /prevention of UV-induced DNA damage.
3. To assess whether the level of sunscreen protection can be adapted to changing UV levels.
4. To assess how fish with UV colours that are able to see in the UV and communicate with these colours cope with changing UV levels.

Background

Many reef fish have UV-reflecting colours invisible to our own eyes. The current hypotheses for reef fish colours are based on camouflage and/or communication. However, neither hypothesis explains why some reef fish that have UV-reflecting colours despite their own inability to see in the UV (Siebeck & Marshall 2001). Here, we will test a new hypothesis that UVR-reflecting colours help prevent UVR-induced DNA damage by reducing the amount of damaging radiation reaching the skin, just like the zinc creams we use to reflect UVR away from our skin.

Mucous cells in the epidermis continuously secrete mucus, covering the body of the fish. UV-absorbing mucus is secreted by the skin of many fish (Zamzow & Losey, 2002) thereby protecting the skin from UV damage, although at the cost of reducing the strength of UV body colours. We have recently quantified and identified these as mycosporine-like amino acids (MAAs) in a range of parrotfish species (Eckes et al. 2008). We discovered that the quantity and the combination of MAAs appear to be highly variable between individuals of the same species sampled at different geographical locations. Part of the reason for this variability is age/size, as demonstrated by our recent study that found the UV absorbance of P. amboinensis mucus to increase with size of the fish (Zamzow & Siebeck, 2006). We also showed that other contributing factors are likely to be health, gender and diet (Zamzow, 2004). MAAs are only expressed in the mucus if UVR and MAA-rich food sources are available, as fish cannot synthesise their own MAAs (Zamzow, 2004). Currently, no knowledge exists about how effective these sunscreens really are at preventing DNA damage and whether the level of protection can be adapted to ambient UVR levels.

Contact Information:

University of Queensland,
St Lucia, QLD 4072
Australia
+61 7 3365 4070

u.siebeck@uq.edu.au
m.eckes@uq.edu.au