Sex and testosterone effects on growth, immunity and melanin coloration of nestling Eurasian kestrels

Abstract

Summary1. Sex differences in testosterone levels and sex-biased sensitivity to testosterone are the basis of some ideas postulated to account for sex-linked environmental vulnerability during early life. However, sex variation in circulating testosterone levels has been scarcely explored and never manipulated at post-natal stages of birds in the wild. 2. We measured and experimentally increased circulating testosterone levels in nestling Eurasian kestrels Falco tinnunculus . We investigated, possible sexual differences in testosterone levels and the effect of this hormone on growth (body mass and tarsus length) and cell-mediated immunity in males and females. We also explored testosterone effects on rump coloration, a highly variable melanin-based trait in male nestlings. We analysed data on circulating testosterone levels of nestlings in 15 additional bird species. 3. Increased levels of testosterone tended to negatively affect body condition, reduced cell-mediated immune responses in male and female nestlings and also diminished the expression of grey rump coloration in male nestlings. No sex differences were observed in testosterone levels in either control or increased testosterone group nestlings, and no interactions were found between sex and treatment. However, male nestlings showed a lower cell-mediated immune response than females in both groups. 4. Our results indicate first, that a high level of testosterone in all nestlings in a brood entails costs, at least in terms of immunity, coloration and probably growth. Secondly, sex differences in post-natal cell-mediated immunity, and consequently in the capacity to prevent diseases, cannot be explained by sex differences in circulating testosterone levels. Finally, by comparing published data at an interspecific level, contradictory sex patterns in circulating testosterone levels have been found, supporting the idea that circulating testosterone might not be a proximate factor causing sex-dependent vulnerability in bird species.

Effects of early developmental conditions on innate immunity are only evident under favourable adult conditions in zebra finches

“…Fargallo et al 2002;Hõrak et al 1999;Saino et al 1997). Second, lower immune responses in large broods might be caused by increased sibling competition resulting in an increase in testosterone (Naguib et al 2004) and a suppressed immune function (Boonekamp et al 2008;Fargallo et al 2007;Folstad and Karter 1992; but see Roberts et al 2004). Evidence for immunosuppressive effects of testosterone, however, is still lacking for zebra finches.…”

The effects of testosterone on immune function in quail selected for divergent plasma corticosterone response

“…There is good evidence of the immunosuppressive nature of T in laboratory mammals (Grossman, 1985), and several manipulative avian studies have found a deleterious effect of elevated T on humoral immunity (Duffy et al, 2000;Peters, 2000;Casto et al, 2001;Buchanan et al, 2003;Owen-Ashley et al, 2004;Deviche and Cortez, 2005), as well as on cell-mediated immunity (Duffy et al, 2000;Casto et al, 2001;Owen-Ashley et al, 2004;Deviche and Cortez, 2005;Boughton et al, 2007;Fargallo et al, 2007). However, other studies have found no such effect on either humoral (Hasselquist et al, 1999;Roberts et al, 2007a) or cellmediated immunity (Buchanan et al, 2003;Greenman et al, 2005;Roberts et al, 2007a).…”

Wing whiteness as an indicator of age, immunocompetence, and testis size in the Eurasian Black-Billed Magpie (Pica pica)

“…Among them, the melanocortin system also regulates a diverse array of physiological functions, including adrenocortical steroidogenesis and anti-inflammatory responses (Cone 2006, Ducrest et al 2008. Relationships among melanin-based phenotypes and immunity (e.g., Gasparini et al 2009, Jacquin et al 2011, Parejo et al 2011; but see González et al 1999;Pärn et al 2005;Fargallo et al 2007a, b), parasite infection (e.g., Fitze and Richner 2002, Chakarov et al 2008, Jacquin et al 2011, testosterone levels (Fargallo et al 2007b, Bókony et al 2008, and corticosterone levels (Pryke et al 2012) have been observed in birds, demonstrating in some cases and suggesting in others that melanic phenotypes can signal immune capacity and endocrine profiles.…”