We measured gaseous lift and specific gravity of larval anurans at regular intervals during development to assess their importance in determining buoyancy in eight species. Specifically, we examined the hatchling, larval, and metamorphic stages of tadpoles from still waters (Limnodynastes dumerili, Limn. peronii, Lithobates septentrionalis, and Rhinella marina), intermittent streams (Litoria genimaculata and Lito. lesueuri), and torrent sections of rivers (Lito. nannotis and Nyctimystes dayi). Buoyancy levels and the strategies used to attain buoyancy varied at different phases of development and with the environment occupied. Buoyancy increased rapidly during development in hatchlings of Limn. peronii, Lith. septentrionalis, and R. marina due to a reduction in specific gravity. Lungs were inflated in early larval stages of all species except for Lito. nannotis, N. dayi, and R. marina, which inflated their lungs following metamorphosis. Limnodynastes dumerili and Limn. peronii used gaseous lift to maintain near-neutral buoyancy throughout larval and metamorphic stages. Lithobates septentrionalis, Stages 25–29 (first summer), possessed a high level of gaseous lift, but buoyancy declined as lung gas volume decreased in Stages 31–43 (second summer). Rhinella marina did not inflate lungs prior to transformation but achieved an intermediate buoyancy level due to a very low specific gravity. The intermittent-stream species Lito. genimaculata and Lito. lesueuri used gaseous lift to achieve buoyancy levels similar to those of Lith. septentrionalis (Stages 31–43) and R. marina. The torrent-dwelling species Lito. nannotis and N. dayi were the least buoyant; their lungs were not inflated prior to transformation and their specific gravity was elevated. Both gaseous lift and specific gravity are important factors in determining buoyancy in larval anurans.
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Vol. 68 • No. 1