Hormonal partner compatibility: a new currency for pair quality

Androgens play major roles in the conserved vertebrate reproductive axis (i. e. hypothalamus-pituitary-gonads). In recent years evidence has been accumulated showing that also androgens may be affected by the interactions between conspecifics, which suggests a mutual interaction between androgens and behavior. It is adaptive for an individual to adjust its sexual and agonistic motivation to changes in its social environment. Thus, male-male interactions stimulate the production of androgens and the levels of androgens are a function of the stability of the male`s social environment (`Challenge hypothesis`, Wingfield et al. 1990). Studies based on this hypothesis have, so far, focused on the `androgen responsiveness` (AR sensu Wingfield et al. 1990: physiological maximum response androgen level divided by the average breeding baseline androgen level) as an independent currency to be compared within, as well as between avian species. Recently, the predictions of the `Challenge hypothesis` have been tested for their robustness to phylogenetic control and their applicability throughout the vertebrates. Notably, among birds and teleosts the effect of paternal care on AR disappeared after control for phylogeny, whereas the effect of mating system remained robust. Given these results, the question arises whether the males` AR is indeed the optimal currency for examining the modulator role of mating behavior on androgen patterns in males from monogamous species and males from polygamous species throughout all vertebrates. Moreover, focusing on only one sex (i. e. the male`s AR) may not be satisfactory when studying the effect of mating strategy, which clearly involves interaction parameters of the male with one or more females, as well as with its social environment. Therefore, the present project will test a new currency: the hormonal partner compatibility as a dyadic pairbond- specific measure, which derives from androgen measures of both, the male and the female of a pair. I presently propose to monitor the effects of mating strategy and the stability of the social environment on the `within-pair testosterone compatibility` (TC) in selected avian species. I will test the validity of this new currency in a comparative approach, by comparing the results from closely related species with different mating systems, i. e. the monogamous Greylag goose (Anser anser) with the polygynous domestic goose (A. domesticus), and the monogamous and biparental Chinese painted quail (Excalfactoria chinensis) with the promiscuous and maternal Japanese quail (Coturnix coturnix japonicus). To approach the causality of the proposed relationship between the TC and reproductive success I suggest to test whether social instability (by means of group composition, group density and extra-pair parentages) may disturb existing hormonal compatibilities in quail and in geese. The influences of biparentality and of partner-related investment on TC will be disentangled by experimentally removing the clutches from selected pairs of domestic geese. The aim of this study is to introduce dyadic hormonal currencies as an emerging general principle in vertebrate behavioral endocrinology, which may potentially allow a further view of Wingfield`s `Challenge hypothesis` across different vertebrate taxa.