Interplay of temperature and light influences wild guppy (Poecilia reticulata) daily reproductive activity

In this study we investigated the environmental regulation of daily reproductive activity of guppies (Poecilia reticulata). We observed male guppy reproductive behaviour for 17 days over three time periods (dawn, noon, and dusk) while recording natural variation in water temperature and light level. Water temperatures recorded during the experiments were highly variable (up to 7 °C per day), and there was a recurring pattern in daily variation for both light and temperature. Levels of activity were highest at dawn and similarly low during noon and dusk, but reproductive behaviour was recorded throughout the day. Mixed‐effects models indicate that light and temperature affect reproductive behaviour differently at different times of the day, and can also have opposing effects. We suggest that the environmental heterogeneity of streams in Trinidad has led to a broad thermal tolerance, and has contributed to the high level of phenotypic plasticity in the guppy and its success as an invasive species. Furthermore, our results show that daily variation in temperature and its interaction with light should be considered in future studies of guppy reproductive behaviour. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 511–520.