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8 - Endocrinology
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- By Stephan J. Schoech, University of Memphis, S. James Reynolds, University of Memphis, Present address: University of Birmingham, Raoul K. Boughton, University of Memphis
- Edited by Walter D. Koenig, University of California, Berkeley, Janis L. Dickinson, University of California, Berkeley
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- Book:
- Ecology and Evolution of Cooperative Breeding in Birds
- Published online:
- 02 December 2009
- Print publication:
- 22 April 2004, pp 128-141
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- Chapter
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Summary
In the nearly 80 years since Skutch (1935) coined the term “helper-at-the-nest,” cooperative breeding has attracted considerable interest, to no small extent because helping to raise non-descendant young violates a primary tenet of Darwinian theory. This “paradox” of how cooperative breeding could have evolved and subsequently have been maintained was partially resolved first by Hamilton (1963), who introduced the concept of kin-selected benefits by individuals that assist in rearing related individuals other than their own offspring, and later by Brown (1978), Koenig and Pitelka (1981), and Emlen (1982a), who developed the hypothesis that cooperatively breeding species were constrained by specific habitat requirements that induced philopatry, thus setting the stage for helping behavior.
Here we focus on the contributions of field endocrinology to our proximate-level understanding of cooperative breeding. Given that hormones are involved in mediating virtually all aspects of an organism's life and affect functions as diverse as gut absorption, blood production, and reproductive and agonistic behaviors, we can expect that they will also play an important role in the various kinds of cooperative and competitive interactions characteristic of cooperative breeders.
BACKGROUND
Reproductive hormones
Two endocrine axes are of primary interest here: the hypothalamo-pituitary-gonadal (HPG) axis and the hypothalamo–pituitary–adrenal (HPA) axis. The HPG axis consists of a region of the forebrain known as the hypothalamus, the pituitary that lies immediately below, and the gonads (Fig. 8.1). In response to stimulatory environmental or endogenous cues, the hypothalamus secretes gonadotropin-releasing hormone (GnRH).
Diet quality during pre-laying and nestling periods influences growth and survival of Florida scrub-jay (Aphelocoma coerulescens) chicks
- S. James Reynolds, Stephan J. Schoech, Reed Bowman
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- Journal:
- Journal of Zoology / Volume 261 / Issue 3 / November 2003
- Published online by Cambridge University Press:
- 22 October 2003, pp. 217-226
- Print publication:
- November 2003
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- Article
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Food availability is one of the most important determinants of successful reproduction in birds. In a previous study, it was shown that Florida scrub-jays Aphelocoma coerulescens maintained a third egg mass when supplemented with a high fat and high protein diet during pre-breeding, as opposed to birds that were not supplemented that laid third eggs markedly lighter in mass than first- and second-laid eggs. Increases in egg quality promote chick growth and survival in many avian species. In this study, scrub-jays were provided with supplements throughout the pre-laying and nestling periods of 2001 and 2002 to investigate whether diet quality influenced growth and survival of chicks. Fledging success and survival to independence of unsupplemented chicks were higher for 2002 compared with 2001 indicating that breeding conditions (e.g. natural food availability) for jays were probably improved in the former year. Consistent growth patterns were found during the first 11 days post-hatch between chicks on supplemented and those on unsupplemented territories. Of the three growth measures, only seventh primary feather growth tended to be greater for third-hatched chicks on supplemented territories compared with third-hatched chicks on control territories. Food supplementation influenced survival of chicks. Compared with chicks hatching on unsupplemented territories, fledging success of chicks hatching from second-laid eggs was significantly greater in 2001, but not in 2002. Chicks from third-laid eggs on supplemented territories also tended to survive better in 2001 compared with chicks from unsupplemented territories, but, again, no such effect was found in 2002. We conclude that food supplementation in the pre-laying and nestling periods results in little measurable improvement in chick growth. However, improvements were found in survival of chicks that may be mediated through improvements in egg quality, but also may be the result of changes in foraging strategies of provisioning birds on supplemented territories. Chicks on supplemented territories might be in better body condition than those on unsupplemented ones. Methods other than morphometrics may be required to detect elevations in body condition of chicks raised on supplemented territories.