Abstract

Many amphibian species lay their eggs in ephemeral ponds where competition for resources is high and there is pressure to develop quickly and grow to large metamorphic size. The adaptive nature of rapid growth and metamorphosis is essential for overcoming the intense resource competition and fluctuating oxygen availability observed in ephemeral pools. Low concentrations of dissolved oxygen can influence the duration of developmental phases in aquatic salamander eggs, resulting in extended durations of poorly adapted phases of their lifecycle, or by forcing rapid metamorphosis to smaller sized adults. This study focused on two species of closely related salamanders, Ambystoma maculatum, and Ambystoma opacum, differing by aquatic and terrestrial egg laying preferences respectively. Embryonic development of these two species was studied under laboratory conditions, comparing growth, development, and hatching success in a moist terrestrial environment and in an aquatic environment, under a range of dissolved oxygen concentrations. Because A. maculatum prefers development in aquatic environments with lower dissolved oxygen than the terrestrial habitats of A. opacum, observation of A. maculatum embryos should indicate faster development and/or be larger at metamorphosis, particularly in lower oxygen environments. The study concluded that while A. maculatum developed faster in all treatments, the difference between species was greatest in higher oxygen treatments, instead of the predicted lower treatments. The low oxygen treatment of A. maculatum showed the only significance difference in larval mass among treatments, with a more anaerobic environment producing larger larvae.

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