Phenotypic Variation Through Ontogeny: Thyroid Axis Disruption During Larval Development in the Frog Pleurodema borellii.

FABREZI, MARISSA; CRUZ, JULIO CÉSAR

Frontiers in Ecology and Evolutionn

Frontiers.org

Año: 2021 vol. 9:

Studies of the effects of thyroid hormones on larval development in the frog Xenopusspp. have provided baseline information to identify developmental constraints andelucidate genetic and hormonal mechanisms driving development, growth, and lifehistory transitions. However, this knowledge requires data based on other anuransto complete a comprehensive approach to the understanding of larval developmentaldiversity and phenotypic variation through ontogeny. Mesocosm experiments providerealistic data about environmental conditions and timing; this information is usefulto describe anuran larval development and/or analyze endocrine disruption. In thisstudy, mesocosm experiments of the larval development of the frog Pleurodemaborellii were conducted to explore the consequences of thyroid axis disruption; thesensitivity of tadpoles to the methimazole (2.66 mg/l) and thyroxine (T4) (1.66 mg/l)was compared. These concentrations were selected based on previous studies inPleurodema borellii. We test the effects of methimazole and thyroxine on development inearly exposure (from beginning of larval development) and late exposure, 18 days afterhatching, with doses administered every 48 h. Tadpoles were evaluated 31 days afterhatching. Methimazole caused moderate hypertrophy of the thyroid gland, alterationin the growth rates, differentiation without inhibition of development, and an increaseof developmental variability. Thyroxine produced slight atrophy of the thyroid gland,accelerated growth rates and differentiation, and minor developmental variability. Intadpoles at stages previous to metamorphose, skull development (differentiation ofolfactory capsules, appearance of dermal bones, and cartilage remodeling) seemed tobe unaltered by the disruptors. Moreover, similar abnormal morphogenesis convergedin specimens under methimazole and thyroxine exposures. Abnormalities occurred inpelvic and pectoral girdles, and vent tube, and could have been originated at thetime of differentiation of musculoskeletal tissues of girdles. Our results indicate thatpremetamorphic stages (Gosner Stages 25?35) are sensitive to minimal thyroid axisdisruption, which produces changes in developmental rates; these stages would alsobe critical for appendicular musculoskeletal morphogenesis to achieve the optimalcondition to start metamorphosis.