Increasing Hormonal Control of Skeletal Development: An Evolutionary Trend in Amphibiansстатья
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Дата последнего поиска статьи во внешних источниках: 12 января 2022 г.
Аннотация:The biphasic life history of amphibians includes metamorphosis, a complexdevelopmental event that involves drastic changes in the morphology, physiology andbiochemistry accompanying the transition from the larval to adult stage of development.Thyroid hormones (THs) are widely known to orchestrate this remodeling and, inparticular, to mediate the development of the bony skeleton, which is a model system inevolutionary morphological studies of amphibians. Detailed experimental studies of therole of THs in the craniogenesis of diverse urodelan amphibians revealed that (i) thesehormones affect both the timing and sequence of bone formation, (ii) TH involvementincreases in parallel with the increase in divergence between larval and adult skullmorphology, and (iii) among urodelans, TH-involvement in skull development changesfrom a minimum in basal salamanders (Hynobiidae) to the most pronounced in derivedones (Salamandridae and Plethodontidae). Given the increasing regulatory function ofTHs in urodelan evolution, we hypothesized a stronger involvement of THs in the controlof skeletogenesis in anurans with their most complex and dramatic metamorphosisamong all amphibians. Our experimental study of skeletal development in the hypoand hyperthyroid yellow-bellied toad (Bombina variegata: Bombinatoridae) supportsthe greater involvement of THs in the mediation of all stages of anuran cranial andpostcranial bones formation. Similar to urodelans, B. variegata displays enhancing THinvolvement in the development of cranial bones that arise during larval ontogeny: whilethe hormonal impact on early larval ossifications is minimal, the skull bones formingduring metamorphosis are strictly TH-inducible. However, in contrast to urodelans, allcranial bones, including the earliest to form, are TH-dependent in B. variegata; moreover,the development of all elements of the axial and limb skeleton is affected by THs. Themore accentuated hormonal control of skeletogenesis in B. variegata demonstratesthe advanced regulatory and inductive function of THs in the orchestration of anuranmetamorphosis. Based on these findings, we discuss (i) changes in THs function inamphibian evolution and (ii) the role of THs in the evolution of life histories in amphibians.