Mechanisms of photoperiodic polyphenism in vertebrates

Variation is a fundamental principle of natural and artificial selection. Annual cycles in daylength or photoperiod are an environmental cue that most species in the plant and animal kingdoms use to determine the time of year and the direction of annual changes. Despite phylogenetic variation in mechanisms of light detection, the neural and molecular substrates that transduce photoperiod information are common across vertebrates. However, there is considerable conditional plasticity in the neuroendocrine mechanism that govern seasonal physiology leading to a spectrum of phenotypes within a single species. Here, we cover the phylogenetic history and conditional plasticity that contribute to photoperiodic polyphenisms. This Review presents the current understanding of how light is detected and represented in the vertebrate central nervous system and highlights phenotypic variation in photoperiod responses in amniotes. The Review provides future directions for addressing gaps in understanding how photoperiodic polyphenisms are involved in adaptations to changing environments.