The Effect of Temperature Fluctuations on the Sex Ratio of the Atlantic silverside (Menidia menidia), a Species with Temperature-Dependent Sex Determination

Abstract

Sex determination in vertebrates can occur via genetics, as found in humans, or based on the environment. In the most prevalent form of environmental determination of sex (ESD), the temperature of the environment during development decides the sex of the individual. This is known as temperature-dependent sex determination (TSD). This phenomenon has been studied in reptiles and fishes using constant temperature treatments, but the effects of fluctuating temperatures remain underexplored. Fluctuating temperature treatments are more ecologically relevant and are known to create significant differences in organisms’ physiology. Therefore, it is important to understand how a fluctuating temperature regime interacts with the sex determination process in TSD species. As climate change continues to increase mean global temperature and temperature variance, TSD species are more at risk than ever. This study aims to unpack the ways in which diel fluctuating temperatures impact the sex ratio (and other physiological traits) of a TSD fish, Menidia menida. I exposed M. menidia to three different temperature treatments (constant: 28°C, small fluctuations: 28±2°C, and large fluctuations: 28±4°C) and compared the resulting sex ratios, length-at-age, and CTmax (upper thermal tolerance) values. When reared under fluctuating temperatures, the fish produced a higher proportion of females than the constant temperature treatment. They also had higher CTmax and lower length-at-age values. The results demonstrate that the effect of temperature fluctuations on M. menidia is significant, and that future research should account for fluctuating temperature regimes.