Seasonal changes in prolactin and luteinizing hormone in the polyandrous spotted sandpiper, Actitis macularia

The polyandrous spotted sandpiper (Actitis macularia) is a species characterized by female dominance over males and predominant male parental care. Prolactin (Prl) and luteinizing hormone (LH) were analyzed in plasma samples obtained serially from individuals across different stages of the breeding season. The reproductive status of each sampled individual was known in detail. Similar Prl values were obtained independently by two different assays. Males tended to have higher plasma Prl levels than females throughout the breeding season. Prl was significantly elevated in both sexes by the first few days of incubation. This rapid rise in Prl may indicate its role in brood patch development and the onset of incubation behavior. In males Prl continued to rise during incubation, whereas it remained constant in females. Higher levels of Prl in males than females, especially late in incubation, reflects the greater contribution of males to incubation. LH declined markedly in males and females from prelaying to early incubation. There was a significant negative correlation between Prl and LH among males, especially from the prelaying to early incubation phases of the season. There was no such correlation among females.