&where UV-B Radiation
AMPHIBIAWEB

UV-B Radiation and Amphibian Declines

(23 March 2004)
Andrew R. Blaustein, Professor of Zoology, Oregon State University

There are three types of ultraviolet radiation: UV-A (315-400nm), UV-B (280-315 nm) and UV-C (200-280 nm) (Blaustein et al. 2003). Most biomolecules do not absorb the higher UV-A wavelengths and most of the UV-C radiation is absorbed by stratospheric ozone; however, UV-B is particularly harmful to living organisms. Ambient Levels of UV-B radiation in the atmosphere have risen significantly over the past few decades most likely due to decreases in stratospheric ozone, climate warming and lake acidification. Because amphibian eggs lack shells and adults and tadpoles have thin delicate skin, they are extremely vulnerable to increased levels of UV-B radiation. It is likely that increases in ambient levels of UV-B radiation have significantly contributed to amphibian population declines (Blaustein and Wake 1995). However, the harmful effects of UV-B radiation on amphibians are dependent upon a number of variables. In the last decade, scientists have conducted experiments using multiple species, to understand how UV-B radiation affects amphibians, which species and life stages are the most vulnerable and how increased levels of UV-B may be working synergistically with other factors of decline.


Figure 1. Areas around the world where UV-B field studies have been conducted. Each number represents a species and each letter corresponds to a study. Red letters represent studies that found a negative effect of UV-B radiation, black numbers represent studies that found no effect and the one yellow number represents a positive effect. For more information on each study see the map key (map and key prepared by Rebecca Doubledee 2004).

The Complexities of UV-B and Amphibian Declines

The detrimental effects of UV-B on amphibians varies among species and between populations of the same species. These effects also vary among life stages within the same species. For example, in some species developing embryos die when exposed to low levels of ambient UV-B radiation whereas the embryos of other species show no overt effects of being exposed to high levels of UV-B radiation. To complicate things even further, in some species the larval stage is more vulnerable than the embryo stage and in other species the most detrimental effects of UV-B radiation occurs after metamorphosis.

Recent work suggests that amphibians have defense mechanisms to combat the harmful effects of UV-B radiation. Some species have an efficient mechanism of repairing UV-induced DNA damage at the molecular level. However, these repair mechanisms vary in efficiency among species and even among life history stages within the same species. Some species have dark pigmentation which may inhibit the penetration of harmful solar rays. Other species avoid UV-B radiation by staying out of sunlight or by being active at night.

The effects of UV-B radiation on amphibians are context dependent. For example, the amount of UV-B radiation an amphibian receives may be dependent upon weather conditions. In some regions, when rainfall is low and amphibians are in shallow water, they may receive higher doses of UV-B radiation than in years when rainfall is greater. The amount of dissolved organic material (DOM) may affect how much UV-B radiation penetrates a body of water. Murky water with good amounts of DOM may impede penetration of UV-B radiation. UV-B radiation may interact synergistically with a variety of agents including contaminants and pathogens (check out our synergisms page for more details!).

We do know that UV-B radiation is harmful to many species of amphibians. However, we do not know how it, or for that matter, any other agent affects amphibians long-term at the population level. Long-term studies of the effects of UV-B radiation are warranted for a fuller understanding of how UV-B affects amphibian populations.

Researchers have found that UV-B radiation can kill amphibians directly, cause sublethal effects such as slowed growth rates and immune dysfunction and work synergistically with contaminants, pathogens and climate change (Kiesecker and Blaustein 1995, Long et al. 1995, Anzalone et al. 1998, Blaustein et al. 1998, Belden and Blaustein 2002a). In the table below, we summarize studies showing the lethal and sublethal effects of ultraviolet radiation alone or in synergism with other factors.

Table 1. Examples of studies showing lethal and sublethal effects of ultraviolet radiation alone or in synergism with other factors. Table modified from Blaustein et al. 2003.

© 2000 Joyce Gross
Species: Western Toad (Bufo boreas)
Effects of UV-B: Exposure to UV-B increases embryo mortality, causes developmental abnormalities and hampers antipredator behavior
Synergism: Exposure to high levels of UV-B increases susceptibility of embryos to infection by a parasitic fungus Saprolignia ferix
References: Worrest and Kimeldorf (1976); Blaustein et al. (1994); Kats et al. (2000); Kiesecker and Blaustein (1995); Kiesecker et al. (2001)

© 2000 Arie van der Meijden
Species: Common Toad (Bufo bufo)
Effects of UV-B: Exposure to UV-B increases embryo mortality and reduces larval survival
References: Lizana and Pedraza (1998); Häkkinen et al. (2001)

© 2002 Nathan Litjens
Species: Common Froglet (Crinia signifera)
Effects of UV-B: Exposure to UV-B increases embryo mortality
References: Broomhall et al. (2000)

© 1991 Michael Frede
Species: Common Tree Frog (Hyla arborea)
Effects of UV-B: Exposure to UV-B causes skin darkening
References: Langhelle et al. (1999)

© 2001 Sean Schoville
Species: California treefrog (Hyla cadaverina)
Effects of UV-B: Exposure to UV-B increases embryo mortality
References: Anzalone et al. (1998)

© 1995 LEAPS
Gray Treefrog (Hyla chrysoscelis)
Effects of UV-B: Exposure to UV-B causes embryonic deformities
References: Starnes et al. (2000)

© 1998 Joyce Gross
Species: Gray Treefrog (Hyla versicolor)
Effects of UV-B: Exposure to UV-B causes skin darkening and decreased swimming activity
Synergism: Exposure to UV-B and carbaryl decreases swimming activity of larvae
References: Zaga et al. (1998)

© Graeme Gillespie
Species: Green and Golden Bell Frog (Litoria aurea)
Effects of UV-B: Adult and larval frogs show behavioral avoidance of high levels of UV-B
References: van de Mortel and Buttemer (1998)

© 2002 Nathan Litjens
Species: Peron's Tree Frog (Litoria peronii)
Effects of UV-B: Adult and larval frogs show behavioral avoidance of high levels of UV-B
References: van de Mortel and Buttemer (1998)

© 2002 Nathan Litjens
Species: Verreaux's Tree Frog (Litoria verreauxii)
Effects of UV-B: Exposure to UV-B increases embryo mortality
References: Broomhall et al. (2000)

© 1996 Glenn McCrea
Species: Pacific Treefrog (Pseudacris regilla)
Effects of UV-B: Exposure to UV-B causes developmental and physiological abnormalities and reduces larval survival
Synergism: Exposure to UV-B in combination with high levels of nitrates reduces larval survival
References:Hays et al. (1996); Ovaska et al. (1997); Hatch and Blaustein 2003

© 1979 Alan Resetar
Species: Western Chorus Frog ( Pseudacris triseriata)
Effects of UV-B: Exposure to UV-B causes embryonic deformities
References: Starnes et al. (2000)

© PENSOFT Publishers
Species: Moor Frog (Rana arvalis)
Effects of UV-B: Exposure to UV-B increases embryo mortality
References: Häkkinen et al. (2001)

© 2000 California Academy of Sciences
Species: Northern Red-legged Frog (Rana aurora)
Effects of UV-B: Exposure of embryos to ambient UV-B radiation in the field negatively affects larval growth and development
References: Belden and Blaustein (2002a)

© 1998 Harry Greene
Species: Cascades Frog (Rana cascadae)
Effects of UV-B: Exposure to UV-B increases embryo mortality, causes retinal damage, developmental and physiological abnormalities and hampers antipredator behavior
Synergism: Exposure to UV-B in combination with increased nitrate levels and low pH, reduces survival and alters behavior
References: Blaustein et al. (1994); Hays et al. (1996); Fite et al. (1998); Kats et al. (2000); Hatch and Blaustein (2000)

© 2002 William Flaxington
Species: American Bullfrog (Rana catesbeiana)
Synergism: Exposure to UV-B and Fluoranthene causes skin damage and hyperactivity
References: Walker et al. (1998)

© 2003 John White
Species: Green Frog (Rana clamitans)
Effects of UV-B: Exposure to UV-B increases larval mortality, delays development and causes morphological abnormalities
References: Grant and Licht (1995); Tietge et al. (2001)

© 2001 Joyce Gross
Species: Northern Leopard Frog (Rana pipiens)
Effects of UV-B: Exposure to UV-B increases mortality, causes deformities in larvae and juveniles and slows the growth and development of larvae
Synergism: Exposure to UV-B and low pH reduces hatching success and exposure to UV-B and fluoranthene causes deformities
References: Long et al. (1995); Ankley et al. (1998); Hatch and Burton (1998); Monson et al. (1999); Smith et al. (2000); Tietge et al. 2001

© J. Harding
Species: Mink Frog (Rana septentrionalis)
Effects of UV-B: Exposure to UV-B increases larval mortality
References:Tietge et al. 2001

© 2003 John White
Species: Wood frog (Rana sylvatica)
Effects of UV-B: Exposure to UV-B causes morphological and behavioral abnormalities
References: Grant and Licht 1997

© 2003 Twan Leenders
Species: Common Frog (Rana temporaria)
Effects of UV-B: Exposure to UV-B delays larval growth and development
References: Pahkala et al. (2001)

© 2002 William Leonard
Species: African clawed frog (Xenopus laevis)
Effects of UV-B: Exposure to UV-B causes skin darkening, decreases swimming activity and reduces growth of larvae
Synergism: Exposure to the combination of UV-B and fluoranthene causes deformities and exposure to the combination of UV-B and carbaryl changes larval swimming behavior
References: Zaga et al. (1998)

© 2002 William Flaxington
Species: Northwestern salamander (Ambystoma gracile)
Effects of UV-B: Exposure to UV-B increases embryo mortality
References: Blaustein et al. (1995)

© 1999 California Academy of Sciences
Species: Long-toed Salamander (Ambystoma macrodactylum)
Effects of UV-B: Exposure to UV-B increases embryo mortality, causes deformities, slows growth and causes skin darkening
Synergism: Exposure to UV-B with nitrates affects growth rates
References:Blaustein et al. (1997); Belden et al. (2000); Belden and Blaustein (2002b); Hatch and Blaustein 2003

© 2001 John P. Clare

Species: Spanish newt (Pleurodeles waltl)
Synergism: Exposure to UV-A enhances the toxicity of polycyclic aromatic hydrocarbons (PAHs)
References:Fernandez and Lharidon (1992); Fernandez and Lharidon (1994)


© 2001 Henk Wallays
Species: Rough-skinned newt (Taricha granulosa)
Effects of UV-B: Exposure ot UV-B increases activity, alters anitpredator behavior and causes skin darkening
References: Blaustein et al. (2000); Belden and Blaustein (2002c)

© 1999 California Academy of Sciences
Species: California newt (Taricha torosa)
Effects of UV-B: Exposure to UV-B increases embryo mortality
References: Anzalone et al. (1998)

© 2003 Franco Andreone
Species: Alpine Newt (Triturus alpestris)
Effects of UV-B: Exposure to UV-B causes skin damage and erratic swimming behavior
References: Nagl and Hofer (1997)

© PENSOFT Publishers
Species: Great Crested Newt ( Triturus cristatus)
Effects of UV-B: Exposure to UV-B causes skin damage and erratic swimming behavior
References: Langhelle et al. (1999)

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