Effects of thiourea on the skull of Triturus newts during ontogeny

Abstract

Background. In amphibians, thyroid hormone (TH) has a profound role in cranialdevelopment, especially in ossification of the late-appearing bones and remodelingof the skull. In the present study, we explored the influence of TH deficiency on boneossification and resulting skull shape during the ontogeny ofTriturusnewt hybrid larvaeobtained from interspecific crosses betweenT. ivanbureschiandT. macedonicus.Methods. Larvae were treated with two concentrations of thiourea (an endocrinedisruptor that chemically inhibits synthesis of TH) during the midlarval and late larvalperiods. Morphological differences of the cranium were assessed at the end of themidlarval period (ontogenetic stage 62) and the metamorphic stage after treatmentduring the late larval period.Results. There was no difference in the ossification level and shape of the skull betweenthe experimental groups (control and two treatment concentrations) at stage 62. Duringthe late larval period and metamorphosis, TH deficit had a significant impact on thelevel of bone ossification and skull shape with no differences between the two treatmentconcentrations of thiourea. The most pronounced differences in bone developmentwere: the palatopterygoid failed to disintegrate into the palatal and pterygoid portions,retardation was observed in development of the maxilla, nasal and prefrontal bonesand larval organization of the vomer was retained in thiourea-treated larvae.Conclusions. This implies that deficiency of TH caused retardation in developmentand arrested metamorphic cranium skeletal reorganization, which resulted in divergentcranial shape compared to the control group. Our results confirmed that skullremodeling and ossification of late-appearing bones is TH–dependent, as in otherstudied Urodela species. Also, our results indicate that TH plays an important rolein the establishment of skull shape during the ontogeny ofTriturusnewts, especiallyduring the late larval period and metamorphosis, when TH concentrations reach theirmaximum