Seasonal covariation in progesterone and odorant emissions among breeding crested auklets (Aethia cristatella) Hector D. Douglas III a,b, ⁎, Alexander S. Kitaysky c , Evgenia V. Kitaiskaia c a Biology Department, Kuskokwim Campus, University of Alaska Fairbanks, Bethel, Alaska 99559, USA b Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA c Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA article info abstract Article history: Received 28 October 2007 Revised 4 February 2008 Accepted 3 March 2008 Available online 25 March 2008 Crested auklets emit a citrus-like odorant that is seasonally modulated, suggesting that it is a secondary sexual trait. We hypothesized that expression of the chemical odorant is facilitated by steroid hormones, similar other secondary sexual traits in birds. Therefore we examined variation in concentrations of hormones in blood plasma and odor production during incubation and early chick rearing. A novel method was used to obtain and measure chemical emissions of crested auklets. Blood plasma samples were analyzed by radioimmunoassay. Progesterone was detected in all birds, and it varied during the breeding season. Octanal emissions covaried with progesterone levels in males but not in females. No seasonal patterns were detected in testosterone, estrogen or DHT, and these hormones were not detected in all breeding adults. Covariance of progesterone and octanal emissions in males suggests there could be at least an indirect relationship between odor emissions and steroid hormones in this species. Thus expression of the citrus-like odorant of crested auklets, like other secondary sexual traits in birds, could be regulated by steroid hormones. © 2008 Elsevier Inc. All rights reserved. Keywords: Chemical signaling Progesterone Steroid hormones Aldehydes Octanal Courtship Introduction Odorants and pheromones mediate reproductive and social behaviors in vertebrates (e.g., mammals: Kruuk et al., 1984; Ferkin and Johnston, 1995; Rasmussen, 2001; Rasmussen and Greenwood, 2003; Smith et al., 2001; Sun and Müller-Schwarze,1998; amphibians: Houck and Reagan, 1990; Houck et al., 1998; Rollmann and Houck, 1999; reptiles: Cooper 1996; Cooper et al., 1996; Lemaster and Mason, 2003). Birds have also been reported to emit odors (Weldon and Rappole, 1997), and studies have documented olfactory capabilities in a number of avian species (Douglas, 2006a,b, 2008; Hagelin et al., 2003; Hagelin and Jones, 2007; Hagelin 2007; Nevitt, 1999; Nevitt et al., 2004; Roper,1999, 2003; Wenzel 1987). Odorants may facilitate reproductive behaviors in birds. For example, female mallards (Anas platyrhynchos) increase production of diester waxes in their uropygial gland during the breeding season, and this biochemical change influences male sexual behavior (Balthazart and Schoffeniels, 1979; Jacob et al., 1979). Seasonal changes in odor production coincident with breeding have long been noted in some Procellariform seabirds (Thibault and Holyoak, 1978). Odors may facilitate nest and mate recognition during the breeding season in the Antarctic prion, Pachiptila desolata (Bonadonna et al., 2007; Bonadonna and Nevitt, 2004) and storm petrels (Grubb 1974; Minguez 1997). Although chemical communication has been recognized in some species of birds during reproduction, the regulation of odor production in birds has received little attention. Steroid sex hormones play an important role in promoting synthesis of some chemical scents in vertebrates (Bohnet et al., 1991; Iwata et al., 2000, 2001; reviewed in Mason 1992; Yamamoto et al., 1996). We suspected that the same could be true in crested auklets, a colonial seabird of Alaska and Siberia that secretes a citrus-like aldehyde odorant during the breeding season (Douglas, 2006a,b,c, 2008). Constituents of the odorant are hexanal, octanal, decanal, (Z)-4-decenal, (Z)-4-dodece- nal, (Z)-6-dodecenal (Douglas et al., 2001, 2004; Douglas, 2006b, 2008). These aldehydes are secreted from translucent hair-like feathers in the bird's interscapular region, and alloanointing helps to distribute the odorant in plumage (Douglas, 2006b, 2008). We hypothesized that an association between the crested auklet's odorant and sex steroids would be expressed during the reproductive season. Crested auklets, like other colonial seabirds of Alaska and Siberia are seasonal breeders (Jones 1993a, Fraser et al., 1999). In seasonal avian breeders sex steroid production is regulated on a seasonal basis. Steroid sex hormones, including testosterone, dihydroxytestosterone, estradiol and progester- one (T, DHT, E 2 ,P 4 , respectively) facilitate expression of secondary sexual traits and reproductive behaviors in birds (Balthazart 1983; Buntin 1996; González et al., 2001; Logan and Carlin, 1991; Logan and Winfield, 1995; Nowicki and Ball, 1989; Ketterson and Nolan, 1992; Silver and Feder, 1973). We predicted that emissions of the chemical odorant would covary with concentrations of circulating steroid hormones among breeding adult crested auklets. In order to test this prediction we measured variation in chemical emissions and circulating concentra- tions of steroid hormones in blood plasma during the breeding season. Hormones and Behavior 54 (2008) 325–329 ⁎ Corresponding author. Biology Department, Kuskokwim Campus, University of Alaska Fairbanks, Bethel, Alaska 99559, USA. Fax: +1 907 543 4527. E-mail address: hddouglas@gmail.com (H.D. Douglas). 0018-506X/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2008.03.003 Contents lists available at ScienceDirect Hormones and Behavior journal homepage: www.elsevier.com/locate/yhbeh