Photoperiod as a reproductive cue in the marsupial genus 'Antechinus': ecological and evolutionary consequences

Abstract

Species in the Australian marsupial genus 'Antechinus' exhibit a short annual mating period which is concluded by the abrupt death of all males. The timing of the annual rut within each of the ten described species varies little from year to year at any given locality, but for some species can differ by up to four months between locations. To determine the influence of photoperiod in regulating the precise interannual synchrony of mating and ovulation, we first investigated populations of each species at over 300 localities throughout their geographical ranges to identify the time of reproduction. We then compared the absolute photoperiod and the rate of change of photoperiod prevailing at the time of reproduction in all population localities. A different, and characteristic, rate of change of photoperiod was correlated strongly with the reproductive timing of four species; there was probably a correlation with reproduction in four more species, but sample sizes were small. For two species, there was no obvious photoperiodic correlation with time of reproduction. There was no evidence that absolute photoperiod or ambient temperature explained the synchrony or narrow timespan of reproduction among any species of Antechinus. Different species-specific ovulatory responses to photoperiod appear to separate the timing of reproduction in sympatric species, with the larger member of species pairs usually breeding first. We suggest that photoperiodic cues (1) allow females to produce young during seasons when food is most reliable and abundant and their energetic demands are maximal; (2) facilitate allochronic isolation between sympatric congeners, and (3) maximize body size differences and hence ecological separation between species.