The combined effects of temperature and aromatase inhibitor on metamorphosis, growth, locomotion, and sex ratio of tiger frog (Hoplobatrachus rugulosus) tadpoles.

Yun Tang,Guo-Hua Ding,Jing-Yi Chen,Xiang Ji,You-Fu Lin,Zhi-Qiang Chen

doi:10.7717/peerj.8834

Abstract

BackgroundThe tiger frog (Hoplobatrachus rugulosus) is widely raised by many farms in southern region of China as an economically edible frog. The growth, development, and sexual differentiation of amphibians are influenced by temperature and steroid hormone level. However, the problem of hormone residues is caused by the addition of exogenous hormones in frog breeding, it is worth considering whether non-sterol aromatase inhibitors can be used instead of hormones.MethodsIn our study, H. rugulosus tadpoles were subjected to two water temperatures (29 °C and 34 °C) and three letrozole concentrations in the feed (0, 0.1 and 1 mg/g) to examine the effects of temperature, aromatase inhibitor and their interaction on metamorphosis, locomotion, and sex ratios. A G-test and contingency table were used to analyze the metamorphosis rate of tadpoles and the survival rate of froglets after feeding for 90 days. A G-test was also used to analyze sex ratios in different treatment groups.ResultsMetamorphosis time and body size (snout–vent length, body mass and condition factor) were significantly different between the two temperature treatments. Metamorphosis time was longer and body size was increased at 29 °C compared to those at 34 °C. Letrozole concentration and the temperature × letrozole interaction did not affect these variables. The jumping distance of froglets following metamorphosis was positively associated with the condition factor; when controlling for condition factor, jumping distance was not affected by temperature, letrozole concentration and their interaction. Temperature and letrozole concentration also did not affect metamorphosis and survival rate. Sex ratio of the control group (0 mg/g letrozole) was 1:1 at 29 °C, but there were more males at 34 °C. The sex ratios of H. rugulosus treated with letrozole at 29 °C and 34 °C were significantly biased toward males, and male ratio increased as letrozole concentration increased. Furthermore, more males were produced at 34 °C than at 29 °C at each letrozole concentration.

Highlights

The growth and sex differentiation of amphibians are often influenced by the environment, and the effect of temperature has received much attention from researchers
Our results showed that the metamorphosis time of H. rugulosus tadpoles at high temperature was shorter than that at low temperature, but the body size of froglets decreased
Our results showed that treatment with letrozole at different concentrations had no significant effect on metamorphosis time or body size of H. rugulosus froglets, which suggests that letrozole concentration does not significantly affect their growth or development

Summary

Introduction

The growth and sex differentiation of amphibians are often influenced by the environment, and the effect of temperature has received much attention from researchers. Previous studies reported that tadpoles experiencing extreme temperatures exhibited a significant shift in phenotypic sex ratio of the offspring (Nakamura, 2009). Tadpoles from families such as Bufonidae, Ranidae, and Dicroglossidae are biased toward developing as males at high temperatures and females at low temperatures (Li et al, 2001; Li, You & Lin, 2007; Dournon, Houillon & Pieau, 1990; Piquet, 1930; Yoshikura, 1959; Hsü, Yü & Liang, 1971; Fu, 2010). Methods: In our study, H. rugulosus tadpoles were subjected to two water temperatures (29 C and 34 C) and three letrozole concentrations in the feed (0, 0.1 and 1 mg/g) to examine the effects of temperature, aromatase inhibitor and their interaction on metamorphosis, locomotion, and sex ratios. More males were produced at 34 C than at 29 C at each letrozole concentration

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