Effect of Sex, Stage of Reproduction, Season, and Mate Removal on Prolactin in Dark-Eyed Juncos

Abstract

Prolactin has been associated with incubation and brooding in passerine birds, but its possible association with other parental behaviors remains unclear. We measured plasma concentrations of prolactin (prl) in Dark-eyed Juncos (Bunco hyemalis), a species in which only females incubate and brood but both sexes feed nestlings. Breeding males and females were bled at the time their eggs hatched, and half the males were taken from their territories. Females and the remaining males were bled again when their young left the nest. Removed males were quickly replaced by new males, some of which we caught and bled. Replacement males courted the females but rarely fed their predecessors' young. Removed males were held in an aviary and bled again in late summer. Prl concentrations were higher in females than males, both at hatching and at nest leaving. Female prl was higher at hatching than at nest leaving and did not vary seasonally. Male prl was higher at hatching than at nest leaving and higher earlier in the season than later. Rearing young alone had no detectable effect on prl in females. Prl of replacement males was lower than that of fathers at hatching but not at nest leaving. Prl in removed males in the aviary was lower than in fathers at hatching but not at nest leaving. These patterns of prl secretion resemble those in other species that raise more than one brood per season and in which females provide the bulk of parental care. In addition, prl may be associated with male parental behavior in juncos.

Is Mate Provisioning Predicted by Ornamentation? A Test with Northern Cardinals (Cardinalis cardinalis)

“…Males obviously benefit from providing their altricial young with food and there is strong selection for this behavior. Levels of the hormone prolactin are known to vary among species – to increase during the reproductive cycle in males, and to co‐vary with levels of male incubation and male nestling provisioning (Ketterson et al. 1990; Buntin 1996; Brown & Vleck 1998; Lormee et al.…”

“…Males obviously benefit from providing their altricial young with food and there is strong selection for this behavior. Levels of the hormone prolactin are known to vary among species -to increase during the reproductive cycle in males, and to co-vary with levels of male incubation and male nestling provisioning (Ketterson et al 1990;Buntin 1996;Brown & Vleck 1998;Lormee et al 1999Lormee et al , 2000Vleck et al 2000;Duckworth et al 2003;Van Roo et al 2003). The influences of hormones on mate feeding (during courtship and incubation) have not been investigated and it is unknown whether levels of prolactin co-vary with this behavior.…”

Does prolactin mediate parental and life-history decisions in response to environmental conditions in birds? A review

“…For instance, incubation starts in doves and pigeons before prolactin levels begin to rise (Silver, 1984) and prolactin levels are not correlated with parental provisioning or brood defense behavior in several studies (Ketterson et al, 1990;Silverin and Goldsmith, 1984;Kosztolanyi et al, 2012;Wojczulanis-Jakubas et al, 2013). Another striking example highlighted by Williams (2012) is the prolactin cycle of the brood parasitic brown-headed cowbird: Despite the absence of incubation behavior and parental provisioning, prolactin levels increase in this species in the same way as many other species that provide intense parental care (Dufty et al, 1987).…”

Why do New World monkey fathers have enhanced prolactin levels?

“…28 For birds it is known that environmental stimuli that accompany parental care are important for the maintenance of elevated PRL levels. 29,30 In the biparental ring dove, both tactile stimulation during incubation and visual stimulation by watching the incubating mate lead to enhanced PRL secretion. 31 Although tactile stimulation of callitrichid fathers during infant-carrying cannot alone explain enhanced PRL levels, infant characteristics are likely to be stimuli for enhanced PRL levels in fathers.…”