Variability in egg hatching time as evidence of a bet-hedging strategy in Japanese medaka (Oryzias latipes)

Abstract

Understanding life-history strategies is essential for developing a clear picture of how organisms have evolved and how they may perform under future conditions. Bet-hedging is a life-history strategy that allows populations to persist in unpredictable, variable conditions. It is a risk reduction strategy that lowers generational fitness while decreasing fitness variability across generations, enabling lineage survival when conditions are not optimal. As such, it may be a favourable life-history strategy as conditions become increasingly variable due to climate change. Japanese medaka (Oryzias latipes) is a small fish that lives in an extremely variable habitat in the wild. It is commonly used as a model organism for toxicology, oncology, and developmental studies. A robust understanding of their life-history parameters is therefore necessary to determine the effects of different treatments in these studies. These fish demonstrate significant variability in egg hatching times, which does not appear to be influenced by external conditions. The goal of this study was to quantify within-clutch and within-population variability and to determine whether both were consistent across different environments, which would support a bet-hedging theory in medaka egg hatching time. For this study I isolated clutches and determined the hatching dates of the eggs to quantify variability. 24 experimental tanks contained four operational sex ratios (OSR; sexually active males:sexually active females), which allowed for comparison of higher-stress vs lower-stress environments. Maternal size and clutch size were also considered. The observed similarity in variability across all treatments provides support for a bet-hedging theory.