beheco.oxfordjournals.org
Amélie N. Dreissa, Carlos Navarrob, Florentino de Lopec and Anders P. Møllerd
a Laboratoire Fonctionnement et Evolution des Systèmes Ecologiques, Université Pierre et Marie Curie-Paris 6, Paris, France b Departamento Ecología Funcional y Evolutiva, Consejo Superior de Investigaciones Científicas, Almería, Spain c Departamento de Biología Animal, Universidad de Extremadura, Badajoz, Spain d Laboratoire de Parasitologie Evolutive, Université Pierre et Marie Curie-Paris 6, Paris, France
Address correspondence to A.N. Dreiss, who is now at the Department of Ecology and Evolution, University of Lausanne, Biology Building, CH-1015 Lausanne, Switzerland. E-mail: amelie.dreiss@unil.ch.
Abstract
The second and fourth digit length ratio (2D:4D) is sexually dimorphic in many vertebrates. This ratio has been suggested to provide an estimate of steroid levels encountered during prenatal development, which may have organizational consequences for physiology and behavior of adults. However, recent studies showed that the relation between digit ratio and steroids seems inconsistent and may vary among species and populations. We tested the hypothesis that digit ratios would be correlated with the expression of secondary sexual characters, using the barn swallow (Hirundo rustica) as a model system. This was done by testing whether variation in 2D:4D ratio was correlated with tail length and features of song, which are important secondary sexual characters positively correlated with circulating steroid concentration in adult birds. Furthermore, we examined the prediction that male and female digit ratios would correlate with body mass in an antagonistic way. There was no significant sexual dimorphism in digit ratio, which may be due to low levels of sexual selection in this population. Adult right 2D:4D ratio was negatively linked to tail length but not to male song output. Moreover, right 2D:4D ratio was negatively correlated with body mass in male and positively in females. These results are consistent with high digit ratios reflecting low levels of testosterone in this bird species.
Key words: bird song, digit ratio, Hirundo rustica, morphology, secondary sexual characters.
Received 16 November 2006; revised 11 September 2007; accepted 17 September 2007.
