Abstract
Hummingbirds present a unique combination between extremely high life costs and a number of efficient adaptations to fuel these demands. In addition to cognitive abilities, territorial hummingbirds display aggressive behaviors that allow for access to better food resources. In year-round territorial species, male–male territorial aggression is similar between breeding and non-breeding seasons; however, the endocrine mechanisms underlying control of territoriality during these distinct seasonal periods may differ. In many species, testosterone (T) triggers increased aggression during the breeding season whereas territoriality in the non-breeding season can be regulated by circulating the biologically inert sex steroid precursor dehydroepiandrosterone (DHEA) and converting it to T in target tissues. The seasonal hormonal regulation of hummingbird territorial behavior has heretofore been unknown. Our goal was to assess seasonal changes in sex steroids, territorial aggression levels, and body condition during reproductive and non-reproductive seasons in hummingbirds. To validate the use of cloacal fluid (CF) for the study of sex steroids, steroid levels in plasma and CF were correlated in Sephanoides sephaniodes. During the reproductive season, Calypte. anna, Archilochus alexandri, and Selasphorus rufus males showed high levels of T that were positively correlated with aggression, but the relationship between T and body condition was not consistent across species. As expected, T levels in females were significantly lower than in males in all seasons, however still detectable. During the non-reproductive season, CF DHEA of Calypte anna was high and positively correlated with aggressive behaviors and body condition. Our results suggest that hummingbirds display aggressive behaviors that could be linked to different hormones during the breeding and non-breeding seasons.
Zusammenfassung
Aggressionsverhalten, Körperkondition und jahreszeitliche Schwankungen der Sexualsteroidspiegel bei vier Kolibriarten
Kolibris verbinden in einzigartiger Weise eine extrem kostspielige Lebensweise mit einer Reihe von Anpassungsleistungen, um ihren Energiebedarf effizient zu decken. Zusätzlich zu ihren kognitiven Fähigkeiten verfügen territoriale Kolibris über aggressive Verhaltensweisen, die ihnen den Zugang zu besseren Nahrungsquellen sichern. Bei Arten, die ganzjährig Reviere verteidigen, ist die territoriale Aggression zwischen Männchen zur Brutzeit ähnlich wie außerhalb; allerdings können sich die der Steuerung der Territorialität zugrunde liegenden endokrinen Mechanismen während dieser jahreszeitlich klar getrennten Zeiträume unterscheiden. Bei vielen Arten löst Testosteron (T) eine Zunahme des Aggressionsverhaltens während der Brutsaison aus, wohingegen die Territorialität außerhalb der Brutzeit durch den Einsatz des biologisch inerten Sexualsteroid-Vorläufers Dehydroepiandrosteron (DHEA) reguliert werden kann, welcher dann im Zielgewebe in T umgewandelt wird. Die jahreszeitliche hormonelle Steuerung des Territorialverhaltens bei Kolibris war bislang unbekannt. Unser Ziel war es, jahreszeitliche Schwankungen des Spiegels von Sexualsteroiden, das Ausmaß territorialer Aggression sowie die Körperkondition der Kolibris jeweils während und außerhalb der Fortpflanzungszeit zu ermitteln. Um die Eignung der Kloakenflüssigkeit (cloacal fluid, CF) für die Untersuchung von Sexualsteroiden zu testen, wurden bei Sephanoides sephaniodes die jeweiligen Steroidspiegel in Plasma und CF miteinander in Bezug gesetzt. Während der Fortpflanzungsperiode zeigten Männchen von C. anna, Archilochus alexandri und Selasphorus rufus jeweils hohe T-Spiegel, welche positiv mit dem Aggressionsverhalten korrelierten; das Verhältnis zwischen T und der Körperkondition stimmte jedoch nicht bei allen Arten überein. Erwartungsgemäß lagen die T-Spiegel bei den Weibchen zu allen Jahreszeiten signifikant niedriger als bei den Männchen, waren aber trotzdem nachweislich vorhanden. Außerhalb der Fortpflanzungszeit lag der CF-Wert für DHEA bei Calypte anna hoch und korrelierte positiv mit dem Aggressionsverhalten und der Körperkondition. Unsere Ergebnisse legen nahe, dass die von Kolibris gezeigten aggressiven Verhaltensweisen zur Brutzeit beziehungsweise außerhalb dieser an verschiedene Hormone gekoppelt sein könnten.
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Acknowledgments
This paper is dedicated to the memory of Loreto Godoy. We thank Baggins End Community, and Lee James of Tierra Verde Vegetables for allowing us to work in their properties. We thank Kara Sweeney and Holly Ernest for contacts and sampling help. This research was supported by CONICYT, Postdoc Becas Chile to PGG and the Endowed Professorship in Physiology to JCW, College of Biological Sciences, University of California, Davis and Grant Number IOS-0750540 from the National Science. Foundation to JCW.
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Communicated by L. Fusani.
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González-Gómez, P.L., Blakeslee, W.S., Razeto-Barry, P. et al. Aggression, body condition, and seasonal changes in sex-steroids in four hummingbird species. J Ornithol 155, 1017–1025 (2014). https://doi.org/10.1007/s10336-014-1088-y
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DOI: https://doi.org/10.1007/s10336-014-1088-y