Photoperiodic control of the concentration of luteinizing hormone, prolactin and testosterone in the male emu (Dromaius novaehollandiae), a bird thatbreeds on short days

The objective of this study was to establish, for a short-day breeding bird , the male emu, whether the breeding season is principally controlled by ch anges in photoperiod, and to investigate the endocrine mechanisms involved. Two groups of adult males were subjected to three alternating periods of 1 50-185 days of 14 h light/day (LD) and 10 h light/day (SD) terminating in a 360-day period of LD or SD. Transfer from LID to SD led to increases in pl asma concentrations of luteinizing hormone (LH) and testosterone, after 82 +/- 8 and 73 +/- 3 (SEM) days, and an increase in prolactin concentrations after 115 +/- 12 days. Concentrations of LH and testosterone began to decre ase before transfer back to LD, at a time when prolactin concentrations wer e approaching peak values. Transfer from LD to 360 days of SD resulted in i ncreases in LH and testosterone concentrations, and these terminated after an increase in prolactin concentrations. After transfer from SD to 360 days of LD, plasma concentrations of LH and testosterone began to increase, aft er delays of 222 +/- 24 and 225 +/- 13 days, and were high at the end of th e study, while prolactin values remained depressed throughout. These observ ations clearly show that seasonal breeding in the emu is directly controlle d by changes in photoperiod. The dynamics of the hormonal responses to chan ge of photoperiod suggest that, despite being short-day breeders, the photo regulation of breeding in emus involves mechanisms that are currently accep ted for birds, rather than mechanisms that have been proposed for short-day breeding mammals. The initiation of breeding in emus is due to dissipation of photorefractoriness by short days which leads to an increase in the sec retion of gonadotrophins to levels that are sufficient to support full repr oductive condition. The termination of breeding, while days are still short , is due to the antigonadotrophic action of prolactin which, unusually for birds, increases while the days are still short. In conclusion, breeding ac tivity in male emus is strongly controlled by photoperiod. Emus are short-d ay breeders, but the central mechanisms that regulate the secretion of repr oductive hormones seem to be similar to those previously proposed for long- day breeding birds. The pattern of prolactin secretion in emus suggests an important role for this hormone in the termination of the breeding cycle.