Delayed Breeding in the Cooperatively Breeding Florida Scrub-Jay (Aphelocoma coerulescens): Inhibition or the Absence of Stimulation?

Publication Type:Journal Article
Year of Publication:1996
Authors:SCHOECH, STEPHANJ, Mumme, RL, Wingfield, JC
Journal:Behavioral Ecology and Sociobiology
Date Published:1996
ISBN Number:03405443
Keywords:Aphelocoma, Aphelocoma coerulescens, Corvidae, Garrulus, Garrulus glandarius
Abstract:To determine whether fundamental differences exist in the reproductive physiology of breeder and nonbreeder Florida scrub-jays (Aphelocoma coerulescens), we compared plasma levels of testosterone (T) and luteinizing hormone (LH) in males, and estradiol ( E2) and LH in females. Although male breeders had higher overall T and larger testes, nonbreeders' T paralleled that of breeders, and their testes were more than an order of magnitude larger than regressed testes. Breeder and nonbreeder males had equivalent baseline LH, and equivalent changes in LH following a gonadotropin-releasing hormone (cGnRH-I) challenge. The T, LH and GnRH challenge data indicate that nonbreeder males have functional hypothalamo-pituitary-gonadal (HPG) axes. We found no hormonal evidence of inbreeding suppression in males: nonbreeders that did not live with their mothers and those that did had similar T. Male nonbreeders that were exposed to ${\rm E}_{2}\text{-implanted}$ females had higher T than did controls, suggesting that the lack of within-pair stimulation is a key factor in whether an individual delays breeding. Female nonbreeders had E2 titres equal to or higher than breeders and neither basal LH nor LH following GnRH challenge differed by breeding status. Nonbreeders' ovarian follicles were smaller than breeders', but were larger than they would be during the nonbreeding season. These data suggest that nonbreeders were primed for breeding and were simply waiting for an opportunity or a required stimulus. Female nonbreeders that lived in a territory with an unrelated male breeder had significantly higher E2 than those that remained with their fathers. Similarly, nonbreeders that were captured away from their home territories had elevated E2. However, nonbreeders that lived with their fathers had E2 that was equivalent to breeding females, suggesting that inbreeding avoidance may not be the primary factor leading to delayed breeding in females.
Short Title:Behavioral Ecology and Sociobiology
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith