Altered thyroid hormone levels affect body condition at metamorphosis in larvae of Xenopus laevis

Abstract

Chemical, physical and biological environmental stressors may affect the endocrine system, such as the thyroid hormone (TH) axis in larval amphibians with consequences for energy partitioning among development, growth and metabolism. We studied the effects of two TH level affecting compounds, exogenous l-thyroxine (T ) and sodium perchlorate (SP), on various measures of development and body condition in larvae of the African clawed frog (Xenopus laevis). We calculated the scaled mass index, hepatosomatic index and relative tail muscle mass as body condition indices to estimate fitness. Altered TH levels significantly altered the growth, development, survival and body condition in metamorphic larvae in different directions. While exogeno us T reduced growth and accelerated development, SP treatment increased growth but slowed down development. Altered TH levels improved body conditions in both treatments and particularly in larvae of the SP treatment but to the detriment of lower survival rates in both TH level altering treatments. The hepatosomatic index was negatively affected by exogenous T , but not by SP treatment indicating a lower lipid reserve in the liver in larvae of T treatment. These altered TH levels as caused by several environmental stressors may have an influence on individual fitness across life, as body condition at the onset of metamorphosis determines metamorphic and juvenile survival. Further research is needed to determine synergetic effects of environmental stressors on TH levels and its effects on physiological traits such as metabolic rate.

Differences in responsiveness and sensitivity to exogenous disruptors of the thyroid gland in three anuran species

“…As the substance concentrations tend to decrease over time, we provided static‐renewal conditions analysis every 48 hr. Other studies found methimazole and T4 were found stable during the exposure period (Degizt et al, ; Ruthsatz et al, ). However, the chemical stability of the test substances from this study needs to be confirmed from known stability data (Degizt et al, ).…”

“…Other studies found methimazole and T4 were found stable during the exposure period (Degizt et al, 2005;Ruthsatz et al, 2018).…”

Post-metamorphic carry-over effects of altered thyroid hormone level and developmental temperature: physiological plasticity and body condition at two life stages in Rana temporaria

“…The SMI accounts for the allometric relationship between mass and a body structure, and is a standardized measure of the body condition that can be directly compared among individuals (Peig and Green 2009, 2010; MacCracken and Stebbings 2012). The SMI has been previously employed as a condition index in anuran larvae (Mac-Cracken and Stebbings 2012;Dittrich et al 2016;Ruthsatz et al 2018b;Ruthsatz et al 2019). A high SMI suggests larger energy storages and, thus, a good body condition.…”

“…Any increase in temperatures above this optimum increases SMR and may lead to a small but constant increase in energetic demands. Potential consequences of increased metabolic expenditures in a resource-limited, high density system are reduced growth, developmental rates, or larval survival, which could ultimately affect recruitment to the terrestrial habitat (Rowe and Crandall 2018;Ruthsatz et al 2018b). In contrast to TH level and temperature effects on SMR, effects on body condition were distinct.…”

“…As metamorphosis is an energy-consuming process (Sheridan and Kao 1998;Beck and Congdon 2003), it is advantageous to maintain a low SMR. Therefore, energetics (i.e., SMR and size of energy stores) at the onset and after completion of metamorphosis are important fitness proxies (Steyermark et al 2005;Muir et al 2014;Ruthsatz et al 2018b). We assume that especially SMR at the onset of metamorphosis leads to carry-over effects on energy stores at the end of metamorphosis due to energy allocation during metamorphic climax.…”