PEREYRA, M. E.*; MACDOUGALL-SHACKLETON, S. A.; SHARBAUGH, S. M.; MORTON, M. L.; KATTI, M.; HAHN, T. P.: Relationships between photorefractoriness and reproductive flexibility in cardueline finches.

Photorefractoriness constrains breeding seasons of many birds at mid and high latitudes, and therefore is an important determinant of temporal reproductive flexibility. We used photoperiod manipulations and measured gonadal condition and gonadotropic hormones to study photorefractoriness in Cardueline finches that vary from seasonal to opportunistic breeders: Red and White-winged Crossbills (Loxia curvirostra and L. leucoptera), Pine Siskins (Carduelis pinus), American goldfinches (C. tristis), Common Redpolls (C. flammea), Cassin’s finches (Carpodacus cassinii), and Gray-crowned Rosy-finches (Leucosticte tephrocotis). At one extreme of flexibility, crossbills neither regress gonads on constant long days, nor cease to respond to long days after gonadal regression has occurred on declining day length; they do not become absolutely photorefractory. At the other extreme, Carpodacus finches regress gonads on constant long days, and cease to respond to long days once gonadal regression occurs; they do become absolutely refractory. Among close relatives, flexible taxa (e.g., siskins) and seasonal taxa (e.g., goldfinches) may show characteristics of both refractoriness and a lack thereof. Further, the oldest lineage tested thus far, L. tephrocotis, appears not to become refractory, despite breeding seasonally at high elevations. This suggests that all Cardueline finches possess physiological characteristics that predispose them toward temporal reproductive flexibility. Rigid seasonality in some taxa, with development of absolute photorefractoriness, may have evolved recently in this group.