Ebook Hormones and reproduction of vertebrates (Vol 4 - Birds): Part 2

Part 2 book "Hormones and reproduction of vertebrates (Vol 4 - Birds)" includes content: Stress and reproduction in birds, hormonal regulation of avian courtship and mating behaviors, hormones and regulat ion of parent al behavior in birds, hormones and regulat ion of parent al behavior in birds, en docrine d isruption o f repro duction in birds.
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Ebook Hormones and reproduction of vertebrates (Vol 4 - Birds): Part 2 Chapter 5 Stress and Reproduction in Birds Creagh W. Breuner University of Montana, Missoula, MT, USA Glucocorticoids (GCs) are primary candidates for SUMMARY There is intrinsic conflict between survival and reproduction. This mediating this decision-making process (Wingfield & conflict can be viewed from the perspective of the pace-of-life Sapolsky, 2003). Glucocorticoids are normally maintained framework (an ultimate view), trading off many offspring per year in the blood at relatively low levels that fluctuate on over a short life against few offspring per year over a longer life; it circadian and circannual cycles to regulate energy avail- can also be viewed from a resource-utilization perspective ability and use (Dallman et al., 1994). However, as the level (a proximate view), increasing current reproductive effort vs. self- of challenge increases, the hypothalamus upregulates the maintenance. The hypothalamicepituitaryeadrenal (HPA) axis hormone cascade, resulting in further release of GCs from controls the production of glucocorticoids (GCs) primarily the adrenal gland into the plasma. Elevated GCs then act responsible for mediating this proximate decision-making through receptors in target tissue to alter behavior and process. In field studies, GCs tend to decrease performance physiology in a variety of ways, including glucose mobi- measures associated with reproduction, and increase measures lization through gluconeogenesis (Dallman, Darlington, associated with immediate survival. This chapter investigates the role of GCs in regulating reproductive effort (the proportion of Suemaru, Cascio, & Levin, 1989; Plaschke, Muller, & available energy expended on reproductionda proximate query), Hoyer, 1996), increased lipogenesis (Cherrington, 1999; approaching this question from an ultimate pace-of-life frame- Landys, Piersma, Ramenofsky, & Wingfield, 2004), and fat work. deposition (Dittami, Meran, Bairlein, Totzke, 2006; Yuan, Lin, Jiang, Jiao, & Song, 2008); reduction or abandonment of the reproductive effort (e.g., Silverin, 1986; Wingfield & Silverin, 1986; Love, Breuner, Vezina, & Williams, 2004); promotion of escape behavior (Breuner, Greenberg, & 1. INTRODUCTION Wingfield, 1998; Wingfield et al., 1998; Breuner & Hahn, 2003); and increases in locomotor activity, foraging Animals face an intrinsic tradeoff between survival and behavior, and food intake (see Landys, Ramenofsky, & reproduction. This tradeoff manifests both on ultimate (e.g. Wingfield, 2006 for review). Altogether, elevated GCs are pace of life) and proximate (e.g. resource utilization) levels. thought to appropriately redirect energy and behavior from From an ultimate or pace-of-life perspective, animals face noncritical energy expenditure (e.g., reproduction) towards tradeoffs between longevity and the number of offspring self-maintenance, making them a good tool for the exam- they produce, so that some animals produce few offspring ination of tradeoffs between reproduction and survival. over a long life and others produce many offspring over a shorter life. A proximate or resource-utilization view highlights the tradeoff in resource allocation; animals have a limited amount of resources that they must divide 1.1. Allostasis between self-maintenance and reproduction. Although the Historically, the GC-driven stress response has been viewed consequences of trading off survival and reproduction can as a response to unpredictable events, and distinct from the be dampened when resources are not limited (as in high- circadian rhythm in baseline GC levels (Wingfield et al., quality individuals), the conflict between these two 1998). In the last five to ten years, McEwen and Wingfield components of fitness is virtually ubiquitous. How is this (2003) have been promoting the movement away from conflict mediated within individuals? More specifically, ‘stress’ terminology towards the idea of allostasis, which what proximate physiological mechanisms translate they define as ‘stability through change.’ Generally, the external and internal cues into the decision-making process argument behind allostasis rests on the concept that, ...