Internal structures of Thoropa miliaris tadpole using phase-contrast synchrotron microtomography

Full text: Amphibians are used extensively in physiological studies aimed at generating new insights in evolutionary biology, especially in the investigation of the evolution of air breathing and terrestriality. The approximately 5770 living species of amphibians are grouped into three orders—Gymnophiona (caecilians), Caudata (salamanders), and Anura (frogs and toads). The latter is the largest, including more than 5065 species currently recognized. Anurans present a variety of reproductive modes, most species are direct developers and lay eggs on water and a tadpole hatches and swim in bodies of water till completion of metamorphosis, with a small froglet that abandons the aquatic life [3]. The species Thoropa miliaris present morphological conditions that differentiate it from other species. Tadpoles live in the film of water on rock surfaces at the wet borders of waterfalls in rain-forest areas, and in rock fields of mountain ranges of southeastern Brazil. Although most species in the genus are common and well sampled in collections of natural history museum, little is known of the group's morphology. Application of microtomography (μCT) for the study of frogs is quite recent. Here, we present the first results of the high- resolution non-invasive investigation of external morphology and internal structures Thoropa miliaris tadpoles. Microtomographic images were obtained at the imaging beamline (IMX) at Brazilian Synchrotron Light Laboratory (LNLS). The synchrotron light source is a 1.67T bending magnet of critical energy of 1.7keV; providing monochromatic beam spectrum of 4keV to 25keV and useful photons of up to 25keV in white beam mode. A detailed knowledge of the interior of biological structures and organisms is crucial for a better understanding of their function and evolution. In this work, whole-specimens of Thoropa miliaris in three different larval stages of development were imaged. Phase retrieval algorithm was implemented together with the conventional filtered backprojection reconstruction algorithm using the PYRAFT software developed by the LNLS team. The resulting voxel data sets were visualized with Avizo 8.0. The contrast between the different tissues in the μCT images was sufficient to be able to distinguish complex internal structures, such as liver, notochord, cerebral, crystalline and bone formation. (author)