Collaborative Research: Interactive Effects of Stress and Nutrition on Reproduction in Birds

University Of Memphis, Memphis TN

Investigators

Abstract

Collaborative Research: Interactive Effects of Stress and Nutrition on Reproduction in Birds Stephan J. Schoech & Reed Bowman University of Memphis & Archbold Biological Station Correctly timing breeding is essential for animals to maximize their fitness. To produce young when conditions favor their survival, most organisms rely on a variety of environmental cues. The PIs have used a combination of observational and experimental studies to demonstrate that food quantity and quality influence timing of breeding. Florida Scrub-Jays (Aphelocoma coerulescens) in suburban habitats with access to ad libitum human-provided food always breed earlier than jays in wildland habitat at nearby Archbold Biological Station (ABS). In wildlands, supplementation with diets that differ in fat and protein content confirm that these nutrients act in synergy to advance breeding. Birds given high fat/high protein (HFHP) diets lay earlier than controls and jays supplemented with high fat/low protein diet, increase maternal allocation to eggs, and increase survival of offspring. Additionally, the PIs found a strong trend for increased over-winter survival of HFHP-supplemented adults relative to controls (even though birds are only supplemented from Jan-Mar). Importantly, both suburban and HFHP wildland jays also had lower levels of corticosterone (CORT), the avian stress hormone, than wildland controls. Because CORT can negatively affect the reproductive axis, the link between CORT and nutrition suggests a unique mechanism underlying the initiation of reproduction. The PIs have developed a novel model demonstrating how resources influence stress (CORT), which in turn influences timing of breeding. Unlike other models, this predicts both advanced timing of breeding and reduced between-year variation - consistent with empirical observations. Very early in the breeding season, birds may be stressed by reduced food availability. Although they may be "reproductively primed" by other cues, such as photoperiod, high levels of CORT inhibit reproduction. But as food become more predictable or of better quality, stress levels are reduced, releasing the inhibition, allowing breeding to occur. Field and captive studies will be used to test the hypothesis that stress associated with resource quality and/or predictability is the physiological mechanism by which environmental cues are translated into reproductive decisions. Suburban and HFHP-supplemented jays will be implanted with CORT to determine if it delays reproduction in females with access to ad libitum food. To learn whether the removal of CORT results in earlier activation of the reproductive axis and advanced laying, CORT will be blocked in unsupplemented jays at ABS. The PIs also will evaluate the ultimate effects of resource availability by examining the interactive effects of diet, stress, and time of breeding on egg size, offspring development, and short- and long-term survival. Using captive studies on Blue Jays, the PIs will examine further the interactions between diet and stress and reproduction. These studies allow serial sampling of endocrine responses to food treatments. The PIs will compare reproductive and stress hormones in jays that differ in the predictability in which food is provided. In addition, nocturnal light exposure in the suburbs may be stimulatory to the reproductive axis. This will be tested by comparing a suite of physiological parameters in jays that are exposed to low levels of light during the dark phase of the daily cycle with birds that are not. The interactions between stress, environmental resources, and reproduction have not been thoroughly investigated in free-living species and may be critical in how birds time reproduction. The suburban component underscores how rapid environmental change associated with global patterns of urbanization can influence naturally-selected systems, and illustrates the potential consequences. Florida Scrub-Jays are a declining species and may serve as an important model for an increasing number of other species from many taxa that are or will face similar challenges due to continued loss of habitat in the face of increasing human usage. This project will have benefits at multiple levels. First, Florida Scrub-Jays are a threatened species and this research may provide ways in which the decline in numbers may be slowed. Second, techniques and information gleaned may be used to ameliorate declines in other species. Third, stress has profound negative impacts upon many aspects of an organism's (humans included!) health, and this research (and associated projects) will consider links between stress, nutrition, reproduction, immune function, and survivorship: all of which have important cross-species implications.