Sexual and somatic development of wood frog tadpoles along a thermal gradient. Issue 2 (23rd May 2018)

• Record Type: Journal Article
• Authors: Lambert, Max R.; Smylie, Meredith S.; Roman, Amber J.; Freidenburg, L. Kealoha; Skelly, David K.
• Is Part Of: Journal of experimental zoology. Volume 329:Issue 2(2018)
• Page Start: 72
• Page End: 79
• Publication Date: 2018-05-23
• Subjects: Charnov–Bull -- genotypic sex determination -- GSD -- sex reversal -- temperature dependent sex determination -- TSD; Zoology -- Periodicals; Zoology; Animal Population Groups -- physiology; Zoology; Electronic journals; Periodical; Periodicals; 590
• DOI: 10.1002/jez.2172
• Languages: English
• ISSNs: 2471-5646

Abstract

Abstract: All amphibian species are known to have genetic sex determination. However, a variety of environmental conditions can moderate sexual differentiation, in some cases leading to sex reversal and skewed sex ratios. While there has been a recent focus on chemically‐induced sex reversal in amphibians, temperature can also influence sexual differentiation. Building upon a classic 1929 study by Emil Witschi, we assessed temperature‐mediated sex reversal. Witschi found that the wood frog sex ratio is 100% male at a high temperature (32°C) compared to a 50:50 sex ratio at 20°C. This pattern is consistent with multiple models of environmentally mediated sexual differentiation in vertebrates. To better understand thermally mediated sex reversal, we raised wood frogs at temperature increments of ∼1°C between 19 and 34°C. Mirroring earlier findings, wood frog metamorph sex ratios are indistinguishable from 50:50 at the lowest temperature and entirely male at the highest temperatures. In between, sex ratios become increasingly male‐dominated as temperatures increase, implying a steadily increasing tendency toward female‐to‐male sex reversal in warmer environments. There was no evidence of a threshold temperature effect on reversal patterns. We also show that, compared to males, females metamorphose larger and later in cooler conditions but earlier and smaller under warmer conditions. While the ecological relevance in this species is unknown, these results conform to the Charnov–Bull model of sex determination (in which female‐to‐male sex reversal can increase fitness to genetic females at higher temperatures), suggesting the system would reward further study. GRAPHICAL ABSTRACT: Wood frog tadpole sex ratios are equal at room temperature but become increasingly male‐dominated with warmer rearing temperatures. Male and female tadpole bodies develop differently along a heat gradient, with female tadpoles developing more robustly at cooler temperatures and males developing more robustly at warmer temperatures. Our results suggest temperature‐induced sex reversal may be an important process in the ecology and evolution of wild amphibians.