Abstract
Thiourea is an established disruptor of thyroid hormone synthesis and is frequently used as an inhibitor of metamorphosis. The changes caused by thiourea can affect processes associated with the oxidative status of individuals (metabolic rate, the HPI axis, antioxidant system). We investigated the parameters of oxidative stress in crested newt (Triturus spp.) larvae during normal development in late larval stage 62 and newly metamorphosed individuals, and during thiourea-stimulated metamorphosis arrest in individuals exposed to low (0.05%) and high (0.1%) concentrations of thiourea. Both groups of crested newts exposed to thiourea retained their larval characteristics until the end of the experiment. The low activities of antioxidant enzymes and the high lipid peroxidation level pointed to increased oxidative stress in larvae at the beginning of stage 62 as compared to fully metamorphosed individuals. The activities of catalase (CAT) and glutathione-S-transferase (GST) and the concentration of sulfhydryl (SH) groups were significantly lower in larvae reared in aqueous solutions containing thiourea than in newly metamorphosed individuals. The high thiourea concentration (0.1%) affected the antioxidative parameters to the extent that oxidative damage could not be avoided, contrary to a lower concentration. Our results provide a first insight into the physiological adaptations of crested newts during normal development and simulated metamorphosis arrest.
Highlights
Many groups of animals occupy distinct niches as larvae and adults and experience radical ontogenetic changes, amphibian metamorphosis can be considered the most dramatic of all [1,2]
During transition to the terrestrial environment, which is often richer in oxygen, an adequate response to increased endogenous production of reactive oxygen species is crucial in preventing increased oxidative injuries [59]
A dramatic change in GST expression was noted in animals that left the aquatic habitats after metamorphosis to live mostly in the terrestrial environment, while analogous changes were not observed in species that never leave the aquatic ecosystem [63,64,65]
Summary
Many groups of animals occupy distinct niches as larvae and adults and experience radical ontogenetic changes, amphibian metamorphosis can be considered the most dramatic of all [1,2]. Metamorphosis, as a central amphibian life-history trait, is dependent on the interplay of body growth, developmental progression, and environmental conditions, and the whole process is integrated and controlled by the neuroendocrine system. In terms of the severity of changes during metamorphosis, tailed amphibians (salamanders, urodeles) are between tailless amphibians (anurans), which are characterized by the most drastic alterations, and legless amphibians (caecilian), which undergo the least modification. Remodeling in salamanders includes loss of external gills, closure of gill slits, resorption of tail fins, formation of eyelids and the nasolacrimal duct, as well as loss of Leydig cells in the skin [1,3,4,5].
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