Early birds and extra-pair mates: Do nightly peaks of steroid hormones influence onset of daily behaviors and opportunities for extra-pair mating?

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Nearly all organisms, from bacteria to humans, display daily changes in physiology and behavior. Yet, substantial variation among individual daily rhythms exist; some individuals naturally begin their daily activity early (e.g. morning larks) while some begin their daily activity later (e.g. night owls). The biological reasons that lead to these variations among individuals and the relationships between behavioral rhythms and other important biological processes is still not fully understood. Reproductive steroid hormones (e.g. testosterone and estrogens) play an important role in regulating many reproductive related behaviors. The level of these hormones in blood also display daily rhythms. Using a Eurasian, cavity nesting songbird (i.e. readily nests in boxes provided in the forest), this research will test the hypothesis that variation between individuals in the levels and rhythms of these hormones may be influencing daily behavioral patterns and reproductive success. In many areas of the world an urbanized life-style is leading to altered daily activity rhythms of both human and non-human animals. This study will provide insight into the mechanisms that influence these rhythms and how these rhythms influence the persistence of species. Such information will be vital for providing baseline knowledge needed to address future questions of the causes and consequences of human-induced alterations of animal rhythms. This project will be conducted in collaboration with a German colleague and will provide opportunities for international training of postdoctoral associates, graduate and undergraduate students. The investigators are actively involved in scientific outreach to public audiences, including cultural and knowledge exchange between scientists and tribal college students and instructors. Hormones regulate a wide variety of traits that have been linked with fitness. Steroid hormones (e.g. estradiol and testosterone) display circadian variations in circulating levels. These hormones are also known to interact with the circadian system in lab animals. Little is known about how daily (daytime and nightly) peaks of hormones are linked to the timing of important daily behaviors or fitness. In songbirds, extra-pair copulations often occur during the pre-dawn period with the earliest risers having greatest success, suggesting that daily behavioral rhythms, and the mechanisms driving them may have important implications for individual fitness. Using a Eurasian cavity nesting songbird (Parus major) this research will (1) Identify relationships between natural variation in daily steroid concentrations and behavioral rhythms. (2) Experimentally test the hypothesis that circulating levels of steroids influence the expression of circadian behaviors (onset of activity and dawn song). (3) Quantify the relationship between daily rhythms, peak hormone levels, and reproductive success. To address these aims, daily behavioral rhythms will be quantified through the use of an automated telemetry recording system, combined with behavioral observations and Radio-Frequency ID (RFID) readers on nest boxes. Hormones will be measured in blood samples collected at night from roosting birds in the pre-laying period as well as during the day. Hormone manipulations will be employed for experimental studies, and effects on rhythms and reproductive success will be documented. Reproductive success will be quantified via monitoring of all nests in a breeding population and genetic parentage analysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.