Non-breeding gonadal testosterone production of male and female Northern Cardinals (Cardinalis cardinalis) following GnRH challenge

Does a short-term increase in testosterone affect the intensity or persistence of territorial aggression? — An approach using an individual's hormonal reactive scope to study hormonal effects on behavior

“…The use of GnRH injections as an indicator of gonadal activity in wild birds has been pioneered by John Wingfield [26] and since then this approach has been extensively used by many researchers to study the gonadal potential to produce testosterone in free-living wild birds (e.g. [15,17,19,20,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]). However, such GnRH injections have been rarely used as a means to test the effect of brief elevations in testosterone on the behavior of free-living animals (but see [47]).…”

Testosterone might not be necessary to support female aggression in incubating northern cardinals

“…Furthermore, the annual T profile of female cardinals is nearly identical to that of males (Jawor, 2007). Prior work with the population assessed here also suggests that female cardinals can significantly increase T concentrations in response to standardized gonadotropin-releasing hormone (GnRH) injections during the nonbreeding through prebreeding periods (see DeVries, Holbrook, Winters, & Jawor, 2011;Jawor, Hooker, & Mohn, 2014, for further details) but not during offspring feeding (DeVries & Jawor, 2013). Given that female cardinals are highly aggressive at the nest and have considerable concentrations of circulating T year-round, we hypothesize that a relationship exists between T and maternal aggression in this species.…”

“…All simulated intrusions were performed and all birds were captured and processed (blood collected, banded) between 0600 and 1200 hours. Upon capture, time of removal from net was noted and birds were processed following procedures previously described for cardinals (DeVries et al, 2011(DeVries et al, , 2012. Processing included blood collection (brachial vein puncture) for T and corticosterone (CORT) analyses, banding individuals (U.S.…”

“…We analysed testosterone using an enzyme immunoassay (EIA; Enzo Life Sciences, Inc., Farmingdale, NY, U.S.A., number 901-065, antibody sensitivity ¼ 5.67 pg/ml plasma) following methods outlined in DeVries et al (2011DeVries et al ( , 2012 and Jawor (2007). This assay has fairly low cross-reactivity with other androgens (testosterone 100%; 19-hydroxytestosterone 14.6%; androstendione 7.2%; dehydroepiandrosterone 0.72%; and oestradiol 0.40%).…”

“…Relationships between aggression scores and year assessed, day of incubation, mass, time of closest approach to the decoy and time until capture were also nonsignificant (all F values < 1.75, all P values > 0.24). Because T levels can increase with time following aggressive interactions, we compared T and CORT in individuals captured before and after 15 min (post-simulated nest intrusion) as this is an accepted time point for when T concentrations might increase based on hypothalamicepituitaryegonadal axis functioning (DeVries et al, 2011(DeVries et al, , 2012Jawor et al, 2007). We found no effect of time on T concentrations (females captured pre-15 min, N ¼ 11; females captured post-15 min, N ¼ 18; t 27 ¼ 1.5, P ¼ 0.14) or on CORT concentrations (pre-15 min, N ¼ 11; post-15 min, N ¼ 15; t 24 ¼ 0.17, P ¼ 0.86).…”