title: Side-specific effect of yolk testosterone elevation on second-to-fourth digit ratio in a wild passerine.
abstract: Second-to-fourth digit ratio is a widely investigated sexually dimorphic morphological trait in human studies and could reliably indicate the prenatal steroid environment. Conducting manipulative experiments to test this hypothesis comes up against ethical limits in humans. However, oviparous tetrapods may be excellent models to experimentally investigate the effects of prenatal steroids on offspring second-to-fourth digit ratio. In this field study, we injected collared flycatcher (Ficedula albicollis) eggs with physiological doses of testosterone. Fledglings from eggs with elevated yolk testosterone, regardless of their sex, had longer second digits on their left feet than controls, while the fourth digit did not differ between groups. Therefore, second-to-fourth digit ratio was higher in the testosterone-injected group, but only on the left foot. This is the first study which shows experimentally that early testosterone exposure can affect second-to-fourth digit ratio in a wild population of a passerine bird.
authors.affiliation: Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány P. sétány 1/C, H-1117, Budapest, Hungary.
authors.forename: Gergely
authors.initials: G
authors.lastname: Nagy
authors.affiliation: Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány P. sétány 1/C, H-1117, Budapest, Hungary.
authors.forename: György
authors.initials: G
authors.lastname: Blázi
authors.affiliation: Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány P. sétány 1/C, H-1117, Budapest, Hungary.
authors.forename: Gergely
authors.initials: G
authors.lastname: Hegyi
authors.affiliation: Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány P. sétány 1/C, H-1117, Budapest, Hungary. janos.torok@ttk.elte.hu.
authors.forename: János
authors.identifier: http://orcid.org/0000-0002-4799-5522
authors.initials: J
authors.lastname: Török
mesh_terms: D000728:Androgens / Q000494:pharmacology; D000818:Animals; D004530:Egg Yolk / Q000737:chemistry*; D004625:Embryo, Nonmammalian / Q000187:drug effects*; D023421:Models, Animal; D020308:Songbirds / Q000033:anatomy & histology* / Q000196:embryology*; D013739:Testosterone / Q000494:pharmacology*; D014034:Toes / Q000033:anatomy & histology* / Q000196:embryology*
chemical_list: D000728:Androgens; D013739:Testosterone
keywords: 2D:4D; Collared flycatcher; Digit ratio; Manipulation; Prenatal testosterone; Testosterone