Social environment affects testosterone level in captive male blue–black grassquits

Abstract

The challenge hypothesis proposes that testosterone (T) elevation above what is needed for breeding is associated with social factors, and males possibly modulate their hormonal response to variations in population density and sex ratio. We investigated the role of social environment in altering testosterone levels and aggression in a tropical, seasonally breeding grassquit (Volatinia jacarina). We exposed males to three social conditions during 1 year: all-males treatment (six males), mixed treatment (three males-three females), and paired treatment (one male-one female). We quantified aggressiveness among males and T plasma concentration for each individual in each treatment monthly. We found that more aggressive interactions occurred in the all-males treatment than in the mixed treatment. The data also revealed that, coincident with these behavioral changes, the patterns of T variation through time in each treatment were markedly different. The all-males treatment exhibited an early increase in T concentration, which was sustained for a lengthy period with two distinctive peaks, and subsequently declined sharply. The mixed treatment presented an intermediate pattern, with more gradual increase and decrease in T levels. At the other extreme, the paired treatment presented a later rise in T concentration. We conclude that the more competitive environment, with higher density of males, caused the early and higher elevation in T level, thus the presence of competitors may influence the decision of how much a male should invest in reproduction. We suggest that the male's perception of his social environment ultimately mediates hormonal production and alters his reproductive strategy.

A multidisciplinary study on social status and the relationship between inter-individual variation in hormone levels and agonistic behavior in a Neotropical cichlid fish

“…The compositions of the social environment (Lacava et al, 2011;, as well as fish previous social status (Oliveira et al, 2009) and age (Alcazar et al, 2014) have all been shown to affect an animal's physiology and the likelihood of becoming T or NT. Thus, in future studies we must reduce social heterogeneity as much as possible, by placing not only size-matched, but individuals with similar backgrounds and experience.…”

“…An animal's social environment can have profound effects on its behavior and physiology (Bernhardt et al, 1998;Chu and Wilczynsku, 2001;Galhardo and Oliveira, 2014;Lacava et al, 2011;Mazuc et al, 2003;Pinto et al, 2011;Sessa et al, 2013). Yet, it is not all up to external factors, as individual's internal environment (i.e.…”

Social Environment Affects Acquisition and Color of Structural Nuptial Plumage in a Sexually Dimorphic Tropical Passerine

“…We collected data monthly from all males from August 2007 until July 2008 that included morphometric, plumage coverage as well as spectral and color measures of the plumage (see below). In a parallel study, we also quantified testosterone plasma concentration and aggression levels of males in the mixed and all males treatments to assess the intensity of social competition [50]. Given the associated variation found for testosterone levels with time and the experimental treatments, direct tests of the association of hormonal levels with the phenotypic variables herein measured would be confounded and therefore we restricted ourselves to the discussion of their associated trends.…”

Androgen responses to reproductive competition of males pursuing either fixed or plastic alternative reproductive tactics

“…One reason might be that androgen levels are not only affected by activational and organizational effects (relative plasticity hypothesis) but, moreover, they have also been shown to be modulated by an individual's social environment (Mazur, 1985;Wingfield et al, 1990;Hirschenhauser and Oliveira, 2006;Lacava et al, 2011). Bourgeois males usually defend and monopolize resources (contest competition) to get access to mates and thus face enhanced levels of social challenges.…”

“…Oliveira and Oliveira, 2014) such as the biosocial model and the challenge hypothesis, which postulate that androgen profiles are influenced by the current social and reproductive environment (e.g. Goymann, 2009;Lacava et al, 2011;Creel et al, 2013;Almeida et al, 2014). The response in androgen levels of focal males to their social/reproductive environment was tested by exposing bourgeois as well as fixed dwarf males and plastic sneaker males to a different social context, while quantifying their hormonal responses.…”