COLLABORATIVE RESEARCH: Timing of Reproduction: Nutrition-Endocrine Interactions

Indiana University, Bloomington IN

Investigators

Abstract

It is essential that animals initiate their reproductive effort at time of year that maximizes the likelihood of successful production of young. If dependent young are present either too early or late in a season, there may be insufficient food for the parents to feed their offspring. Unlike mammals, in which a lactating female converts available food resources into milk to be fed young, most nestling birds are fed insects whose abundance varies seasonally. The PIs noted that in the Florida Scrub-Jay (Aphelocoma coerulescens), jays that live in a suburban habitat begin breeding earlier than jays living in their natural environment (at Archbold Biological Station, ABS) and that one apparent result of early breeding is that suburban-young are in poorer condition and survivorship is lower that it is at ABS. (Effects from causes such as automobiles and pets have been factored out of the analyses). Previous experiments and observations point toward human-provided food as the underlying cause of early breeding in the suburbs. Although food has been shown to be an important factor in the decision of when to begin breeding in females of many species, whether it is specific nutrients within the food, such as proteins (or specific essential amino acids that are the building-blocks of proteins), fats, or a combination of these two is less clear. The PIs will provide females at ABS with food supplements that are high in protein (including essential amino acids), high in fats, or high in both to determine the import of these nutritional cues upon the timing of reproduction. To better understand the physiological mechanisms by which the nutritional cues lead to the initiation of reproduction in female jays the PIs will answer the following questions: 1) Does the presence of a reliable food source, independent of content, lead to early breeding? 2) Are specific nutrients essential in the decision of when to begin breeding and, if so, which nutrient serves as the cue to inform a female when to begin breeding? 3) Are blood or whole body levels of these nutrients key in the female's decision to breed? 4) Is the information about the female's nutritional state communicated by hormonal means and, if so, what are the hormones involved? In addition to determining the effects of the different supplementary diets upon timing of clutch initiation, the PIs will answer the answer the preceding questions by measuring plasma levels of reproductive hormones (luteinizing hormone, testosterone, and estradiol) and total protein. The PIs will also measure levels of leptin, a hormone that is involved in the onset of reproduction in some mammals: this makes it a possible hormonal cue that informs a female that her condition is suitable to begin reproduction. By considering numerous physiological factors, the PIs will learn how an organism integrates nutritional information into its decision of when to begin reproduction. This research will contribute significantly to the understanding of how resource availability affects the behavior, physiology, and fitness of seasonally breeding animals in the sub-tropics, especially the threatened Florida Scrub-Jay.