title: Sexual Dimorphism and Population Differences in Structural Properties of Barn Swallow (Hirundo rustica) Wing and Tail Feathers.
abstract: Sexual selection and aerodynamic forces affecting structural properties of the flight feathers of birds are poorly understood. Here, we compared the structural features of the innermost primary wing feather (P1) and the sexually dimorphic outermost (Ta6) and monomorphic second outermost (Ta5) tail feathers of barn swallows (Hirundo rustica) from a Romanian population to investigate how sexual selection and resistance to aerodynamic forces affect structural differences among these feathers. Furthermore, we compared structural properties of Ta6 of barn swallows from six European populations. Finally, we determined the relationship between feather growth bars width (GBW) and the structural properties of tail feathers. The structure of P1 indicates strong resistance against aerodynamic forces, while the narrow rachis, low vane density and low bending stiffness of tail feathers suggest reduced resistance against airflow. The highly elongated Ta6 is characterized by structural modifications such as large rachis width and increased barbule density in relation to the less elongated Ta5, which can be explained by increased length and/or high aerodynamic forces acting at the leading tail edge. However, these changes in Ta6 structure do not allow for full compensation of elongation, as reflected by the reduced bending stiffness of Ta6. Ta6 elongation in males resulted in feathers with reduced resistance, as shown by the low barb density and reduced bending stiffness compared to females. The inconsistency in sexual dimorphism and in change in quality traits of Ta6 among six European populations shows that multiple factors may contribute to shaping population differences. In general, the difference in quality traits between tail feathers cannot be explained by the GBW of feathers. Our results show that the material and structural properties of wing and tail feathers of barn swallows change as a result of aerodynamic forces and sexual selection, although the result of these changes can be contrasting.
authors.affiliation: Evolutionary Ecology Group, Hungarian Department of Biology and Ecology, Babeş-Bolyai University, Cluj Napoca, Romania; MTA-DE "Lendület" Behavioural Ecology Research Group, Department of Evolutionary Zoology and Human Biology, University of Debrecen, Debrecen, Hungary.
authors.forename: Péter L
authors.initials: PL
authors.lastname: Pap
authors.affiliation: Museum of Zoology, Babeş-Bolyai University, Cluj Napoca, Romania.
authors.forename: Gergely
authors.initials: G
authors.lastname: Osváth
authors.affiliation: Grupo de Investigación de la Biodiversidad Genética y Cultural, IREC-(CSIC-UCLM-JCCM), Ciudad Real, Spain.
authors.forename: José Miguel
authors.initials: JM
authors.lastname: Aparicio
authors.affiliation: Evolutionary Ecology Group, Hungarian Department of Biology and Ecology, Babeş-Bolyai University, Cluj Napoca, Romania; 'Milvus Group' Bird and Nature Protection Association, Tîrgu Mureș, Romania.
authors.forename: Lőrinc
authors.initials: L
authors.lastname: Bărbos
authors.affiliation: Faculty of Biology and Environmental Sciences, Cardinal Stefan Wyszyński University in Warsaw, Warsaw, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Matyjasiak
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Milano, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Rubolini
authors.affiliation: Dipartimento di Bioscienze, Università degli Studi di Milano, Milano, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Saino
authors.affiliation: Evolutionary Ecology Group, Hungarian Department of Biology and Ecology, Babeş-Bolyai University, Cluj Napoca, Romania; MTA-DE "Lendület" Behavioural Ecology Research Group, Department of Evolutionary Zoology and Human Biology, University of Debrecen, Debrecen, Hungary.
authors.forename: Csongor I
authors.initials: CI
authors.lastname: Vágási
authors.affiliation: MTA-DE "Lendület" Behavioural Ecology Research Group, Department of Evolutionary Zoology and Human Biology, University of Debrecen, Debrecen, Hungary.
authors.forename: Orsolya
authors.initials: O
authors.lastname: Vincze
authors.affiliation: Laboratoire d'Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, Orsay Cedex, France.
authors.forename: Anders Pape
authors.initials: AP
authors.lastname: Møller
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005241:Feathers / Q000033:anatomy & histology*; D005260:Female; D008297:Male; D010641:Phenotype; D012727:Sex Characteristics; D046388:Swallows / Q000033:anatomy & histology*; D013623:Tail / Q000033:anatomy & histology*; D014921:Wings, Animal / Q000033:anatomy & histology*