Abstract
Recent anthropogenic influences on freshwater habitats are forcing anuran populations to rapidly adapt to high magnitude changes in environmental conditions or face local extinction. We examined the effects of ecologically relevant elevated salinity levels on larval growth, metamorphosis and survival of three species of Australian anuran; the spotted marsh frog (Limnodynastes tasmaniensis), the painted burrowing frog (Neobatrachus sudelli) and the green and golden bell frog (Litoria aurea), in order to better understand the responses of these animals to environmental change. Elevated salinity (16% seawater) negatively impacted on the survival of L. tasmaniensis (35% survival) and N sudelli (0% survival), while reduced salinity had a negative impact on L. aurea. (16% seawater: 85% survival; 0.4% seawater: 35% survival). L. aurea tadpoles survived in salinities much higher than previously reported for this species, indicating the potential for inter-populations differences in salinity tolerance. In L. tasmaniensis and L. aurea, development to metamorphosis was fastest in low and high salinity treatments suggesting it is advantageous for tadpoles to invest energy in development in both highly favourable and developmentally challenging environments. We propose that this response might either maximise potential lifetime fecundity when tadpoles experience favourable environments, or, facilitate a more rapid escape from pond environments where there is a reduced probability of survival.
Highlights
Organisms are often forced to exist in habitats that undergo rapid and severe environmental change
In order to better understand the ability of Australian frogs to tolerate elevated salinity we examined the effect of ecologically relevant salinity levels on larval growth, metamorphic timing and survival of three species of Australian anuran; the spotted marsh frog (Limnodynastes tasmaniensis), the painted burrowing frog (Neobatrachus sudelli) and the green and golden bell frog (Litoria aurea)
Experimental Design To examine the effects of elevated salinity on larval growth and survival, tadpoles of L. aurea, N. sudelli and L. tasmaniensis were reared under four salinity treatments: 0.4% seawater, 4% sw, 10% sw and 16% sw (0.14 ppt, 1.4 ppt, 3.5 ppt and 5.6 ppt sea salt respectively)
Summary
Organisms are often forced to exist in habitats that undergo rapid and severe environmental change. If changes in environmental condition are of a greater magnitude than a species is able to tolerate, no adaptation can occur, resulting in an increased probability of local extinction, and an associated decline in species diversity [3]. Amphibian populations are in decline, and in Australia alone over 15 percent of frog species (33/217) are currently listed as extinct, endangered or vulnerable [5]. Proposed reasons for these declines have included increased exposure to ultra-violet radiation, acidification, climate change, impacts of introduced species, pathogens such as the virulent chytrid fungus disease, and changes to air and water quality [see review in 3].
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