Adaptive differences in the timing of egg laying between different populations of birds result from variation in photoresponsiveness

Abstract

Although intraspecific variation in reproductive photoresponsiveness has been demonstrated in many bird species, it has never been examined in conjunction with comparative long-term field studies which accurately identified key factors governing local adaptation of life history traits, and rarely in combination with studies of non-domesticated birds that breed in captivity. Furthermore, it is generally assumed that, within species, adaptive differences in photoresponsiveness mainly occur across populations breeding at different latitudes, and that at similar latitudes, interpopulation variations in timing of breeding is mainly caused by proximate responses to variations in micro-climate or food. Considering results of breeding experiments in laboratory conditions in the framework of long-term comparative studies of natural populations, we here provide the first evidence in a bird that adaptive differences in the onset of first clutches between populations breeding at similar latitudes proximately mainly results from variation in responses to daylength.