Inter-Annual Variation of Exogenous Cues Influences Reproductive Phenology of the Longnose Shiner, Notropis longirostris

Abstract

The extent of annual variation in reproductive seasons of subtropical and temperate fishes and the relationship with varying environmental conditions is not well-understood. I investigated the initiation and termination of the spawning season in Notropis longirostris (Longnose Shiner) over a 9-year period in south-central Mississippi and analyzed the influence of photoperiod and thermal time (thermal history) on reproductive readiness (reproductive condition). Reproductive readiness of females across years was related to photoperiod and thermal time, but there was also a significant interaction between these factors reflecting their changing importance during the initiation and termination of reproduction. Thermal time and photoperiod showed an equally strong relationship with reproductive readiness during the initiation phase, whereas photoperiod was a better predictor of reproductive readiness during the termination phase. The beginning of the reproductive season varied more among years than did the end of the reproductive season. The difference appears to be the result of greater annual variation in prevailing environmental temperatures at the beginning than at the end of the reproductive season and the role of photoperiod during the termination of the spawning season. Overall, thermal time appears to synchronize the reproductive cycle with environmental conditions; however, photoperiod eventually outweighs the influence of thermal time. Further investigations of variation in reproductive cycles vis-à-vis environmental variability will facilitate efforts to understand the influence of climate change.