Habitat of Origin and Changes in Water Chemistry Influence Development of Western Chorus Frogs

Caging, but not air deprivation, slows tadpole growth and development in the amphibian Xenopus laevis

Xenopus laevis tadpoles raised in submerged cages in normoxic water develop more slowly than tadpoles raised with access to air. This study distinguishes between the effects of being caged and being deprived access to air on development and growth. Tadpoles were raised in high and low density control tanks and in cages in the same tank that were either completely submerged or with the top exposed to air. Experiments were repeated with the cages in different positions relative to the air stones and with and without the water flow from air stones supplemented with a pump. Whereas caging tadpoles has a large effect on their development and growth, additionally depriving them of air has a small effect and this effect can be removed by optimizing water flow through the cage. The effect of caging, though significant in this study, is small compared to the variation in growth and developmental rates that is commonly encountered within and among controls in lab studies. Caging effects can also be diminished by optimizing rearing conditions and/or having exceptionally vigorous tadpoles. The effects of air deprivation and caging thus pose less of a problem for experimenting on air-deprived (AD) and air-restored Xenopus tadpoles than their inherent variability in growth and developmental rates and their susceptibility to growth and developmental arrest. Further, the effect of air deprivation in this air-breathing amphibian does not pose a conflict with evolutionary hypotheses for lung loss involving lengthening of the larval period and delay in the onset of air breathing.

Relations between conspecific density and effects of ultraviolet-b radiation on tadpole size in the striped marsh frog

Global increases in ultraviolet-B radiation (UVBR) associated with stratospheric ozone depletion are potentially contributing to the decline of numerous amphibian species around the world. Exposure to UVBR alone reduces survival and induces a range of sublethal effects in embryonic and larval amphibians. When additional environmental stressors are present, UVBR can have compounding negative effects. Thus, examination of the effects of UVBR in the absence of other stressors may substantially underestimate its potential to affect amphibians in natural habitats. We examined the independent and interactive effects of increased UVBR and high conspecific density would have embryonic and larval striped marsh frogs (Limnodynastes peronii). We exposed individuals to a factorial combination of low and high UVBR levels and low, medium, and high densities of striped marsh frog tadpoles. The response variables were time to hatching, hatching success, posthatch survival, burst-swimming performance of tadpoles (maximum instantaneous swim speed following an escape response), and size and morphology of tadpoles. Consistent with results of previous studies, we found that exposure to UVBR alone increased the time to hatching of embryos and reduced the burst-swimming performance and size of tadpoles. Similarly, increasing conspecific density increased the time to hatching of embryos and reduced the size of tadpoles, but had no effect on burst-swimming performance. The negative effect of UVBR on tadpole size was not apparent at high densities of tadpoles. This result suggests that tadpoles living at higher densities may invest relatively less energy in growth and thus have more energy to repair UVBR-induced damage. Lower densities of conspecifics increased the negative effects of UVBR on developing amphibians. Thus, low-density populations, which may include declining populations, may be particularly susceptible to the detrimental effects of increased UVBR and thus may be driven toward extinction faster than might be expected on the basis of results from single-factor studies.

Effects of pine invasion on anurans assemblage in southern Brazil coastal ponds

The destruction of wetlands due to afforestation areas is a common activity in temperate and subtropical regions in Southern America. The expansion of pine in the Coastal Plain of Southern Brazil is out of control and its impacts on aquatic biodiversity are little known. We tested the following hypotheses: the pine occurrence diminishes the anuran richness and abundance in ponds and it changes the anuran composition; the beta-diversity between pine and native grassland matrix ponds (natural ponds) is determined mainly by nestedness. Sampling was carried out from 2007 to 2009 in five ponds in pine invasion matrix and five ponds in native grassland matrix. The natural ponds showed a greater richness of tadpoles (10 species) than pine ponds (5 species). The mean richness of adults was higher in natural ponds than pine ponds throughout the entire study. The species composition was different between natural and pine ponds, for both adults and tadpoles. Comparing natural ponds with each other and the pine ponds with each other, our results showed that neither nestedness nor turnover was determinant for beta-diversity. However, when natural ponds were compared with pine ones, we found that the contribution of nestedness was higher for the anurans beta-diversity than turnover. Increases in the nestedness mechanism indicated that the pine occurrence results in species loss in Southern Brazil ponds. Since 90% of its wetland has been already affected, the removal of Pinus in the conservation areas in southern Brazil is important to minimize their impacts on aquatic biodiversity.