Seasonally sympatric songbirds that differ in migratory strategy also differ in neuroendocrine measures

• Published in: General and comparative endocrinology Vol. 285; p. 113250
• Main Authors: Kimmitt, Abigail A., Sinkiewicz, David M., Ketterson, Ellen D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.01.2020
• Subjects: Animal Migration - physiology; Animals; Female; Gonadotropin-Releasing Hormone - genetics; Gonadotropin-Releasing Hormone - metabolism; Heteropatry; Hormone receptors; Hypothalamus - metabolism; Linear Models; Migration; Neurosecretory Systems - metabolism; Quantitative PCR; Reproductive physiology; RNA, Messenger - genetics; RNA, Messenger - metabolism; Seasonal sympatry; Seasons; Songbirds - physiology; Sympatry - physiology; Hormone receptors; Seasonal sympatry; Heteropatry; Reproductive physiology; Migration; Quantitative PCR
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1016/j.ygcen.2019.113250

•Females differing in migratory strategy also differ in reproductive timing mechanisms.•Non-migrants (residents) are more reproductively developed than in migrants.•Top-down stimulation of the reproductive axis is stronger in residents.•Negative feedback of sex steroids on the reproductive axis is greater in migrants.•No support for stress hormones suppressing reproduction at this time point. Seasonally breeding animals initiate gonadal recrudescence when mechanisms that suppress reproduction give way to mechanisms that stimulate it. However, knowledge of mechanistic changes in hormonal regulation during this transition is limited. Further, most studies of reproductive timing have focused on males, despite the critical role of females in determining breeding phenology. Closely related populations that live in the same environment but differ in reproductive timing provide an opportunity to examine differences in mechanisms during the transition from the pre-reproductive to reproductive state. We studied closely related migrant and resident populations of dark-eyed juncos (Junco hyemalis) that reside in the same environment in spring but differ in breeding phenology. Residents initiate breeding earlier than migrants, which do not breed until after they have migrated. To directly study differences in the hypothalamic mechanisms of reproduction, we captured 16 migrant and 13 resident females from the field on March 25-April 11. We quantified expression of mRNA transcripts and show that resident females had higher abundance of gonadotropin-releasing hormone transcripts than migrant females, indicating greater reproductive development in resident than migrant females living in the same environment. We also found higher transcript abundance of estrogen receptor and androgen receptor in migrant than resident females, suggesting that negative feedback may delay reproductive development in migrant females until after they migrate. These differences in hypothalamic mechanisms may help to explain differences in reproductive timing in populations that differ in migratory strategy.