Latitudinal variation in photoperiodic response of the three-spined stickleback Gasterosteus aculeatus in western North America.

Reproductive maturation in both male and female three-spined stickleback Gasterosteus aculeatus was strongly photoperiodic in a northern population (Alaska, 61 degrees N) but not in a southern population (Oregon, 43 degrees N) from western North America. Increasing reliance on photoperiod with increasing latitude is a general phenomenon among vertebrates, and is probably due to the anticipation of a narrower window of opportunity for reproduction and development at higher latitudes.