Comparative Effects of Ambient Ultraviolet‐B Radiation on Two Sympatric Species of Australian Frogs

Abstract

Declines have been observed in a number of Australian frog species, many of these at high elevations. Alpine regions in Australia are likely to be particularly subject to increases in ultraviolet‐B radiation ( UV‐B, 280–320 nm) because UV‐B levels increase with elevation and because anthropogenic depletion of ozone has been particularly severe in the southern hemisphere. We compared survivorship of embryos and tadpoles of a declining species of frog, Litoria verreauxii alpina, with those of a sympatric nondeclining species, Crinia signifera, under three ambient UV‐B treatments, unshielded, control, and UV‐B–excluding. Experiments were conducted in artificial water bodies established at three different elevations (1365, 1600, and 1930 m) in the Snowy Mountains of southeastern Australia. The exclusion of UV‐B significantly enhanced survival of L. v. alpina (declining species) at all elevations. Overall, the probability of dying was highest in the unshielded treatments and lowest under the UV‐B–excluding treatment for both species over all elevations. The probability of dying was significantly higher in L. v. alpina than in C. signifera for a given UV‐B treatment at the two highest elevations. Our results support the hypothesis that ultraviolet radiation is likely to be a contributing factor in the disappearance of L. v. alpina at high elevations in southern Australia.

Drivers of amphibian declines: effects of ultraviolet radiation and interactions with other environmental factors

“…Briefly, field and laboratory studies have shown that exposure to UVR can reduce survival, reduce growth, slow the rate of development, induce developmental malformations and abnormalities, reduce locomotor performance, and cause changes in metabolic rate and behaviour (Table 1). Such lethal and sublethal UVR effects have been observed in the embryos, larvae, metamorphs and adults of Limnodynastes peronii Artificial lamps [147] Lithobates sylvaticus Artificial lamps [93] Litoria aurea Ambient sunlight [177] Pseudacris cadaverina Ambient sunlight [179] Rana aurora Ambient sunlight plus artificial lamps [96] Rana cascadae Ambient sunlight [100] Taricha torosa Ambient sunlight [179] Reduced larval survival Ambystoma laterale Ambient sunlight plus artificial lamps [181] Ambystoma macrodactylum Artificial lamps [78,182] Ambystoma maculatum Ambient sunlight plus artificial lamps [181] Anaxyrus americanus Ambient sunlight plus artificial lamps [181] Artificial lamps [93] Bufo bufo Ambient sunlight [180,183] Crinia signifera Ambient sunlight [114] Hyla versicolor Ambient sunlight plus artificial lamps [181] Artificial lamps [93] Hypsiboas pulchellus Artificial lamps [69] Ichthyosaura alpestris Ambient sunlight [81] Artificial lamps [81] Limnodynastes peronii Artificial lamps [62,65] Lithobates clamitans Ambient sunlight [184] Ambient sunlight plus artificial lamps [181] Artificial lamps [93] Lithobates pipiens Ambient sunlight [184][185][186] Artificial lamps [58] Lithobates septentrionalis Ambient sunlight [184] Lithobates sylvaticus Ambient sunlight [188] Ambient sunlight plus artificial lamps …”

“…However, lower temperatures have also been found to enhance the negative effects of UVR independent of exposure duration. Using a fixed exposure duration, Broomhall et al [114] found that the embryos and tadpoles of the alpine tree frog Litoria verreauxii and brown froglet Crinia signifera suffered greater mortality when exposed to UVR at higher elevations where temperatures were cooler. However, because temperature was confounded with elevation, Broomhall et al [114] could not attribute the greater effect of UVR at higher elevations to cooler temperatures specifically.…”

“…Using a fixed exposure duration, Broomhall et al [114] found that the embryos and tadpoles of the alpine tree frog Litoria verreauxii and brown froglet Crinia signifera suffered greater mortality when exposed to UVR at higher elevations where temperatures were cooler. However, because temperature was confounded with elevation, Broomhall et al [114] could not attribute the greater effect of UVR at higher elevations to cooler temperatures specifically. van Uitregt et al [65] on the other hand, confirmed that cooler temperatures enhance the negative effects of UVR independent of exposure duration by using a controlled laboratory experiment: they found that despite the same exposure duration, the negative effect of UVR on the survival, growth and locomotor performance of L. peronii tadpoles was greater at 20°C than at 30°C.…”

“…van Uitregt et al [65] on the other hand, confirmed that cooler temperatures enhance the negative effects of UVR independent of exposure duration by using a controlled laboratory experiment: they found that despite the same exposure duration, the negative effect of UVR on the survival, growth and locomotor performance of L. peronii tadpoles was greater at 20°C than at 30°C. Broomhall et al [114] and van Uitregt et al [65] both hypothesised that the apparent thermal-dependence of UVR effects may therefore also be due to the reduced activity of the enzymes involved in defending against UVR damage at lower temperatures.…”

Amphibian Biology and Husbandry

“…The role of UV-B in amphibian physiology is less clear (Gehrmann 1994). Studies of the effect of ultraviolet light on amphibians have emphasized its deleterious effects on eggs and embryos (e.g., Blaustein and Belden 2003;Blaustein et al 1997;Broomhall et al 2000; but see also Licht and Grant 1997 for a contrasting opinion); however, the behavior of some species of frogs exposes them to direct solar radiation for hours at a time (Brust and Preest 1988;Lillywhite 1970;Seymour 1972). Fluorescent bulbs with high UV-B output had no apparent ill effects on the growth of juvenile Wyoming toads (Bufo [ Anaxyus ] baxteri) (R.K. Browne, Perth Zoo, South Perth, Western Australia, personal communication, 2006), but larval salamanders (Ambystoma macrodactylum and Ambystoma gracile) that were exposed to UV-B grew more slowly than individuals that received only full-spectrum illumination (Belden and Blaustein 2002).…”