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Sexual Dimorphism and Population Differences in Structural Properties of Barn Swallow (Hirundo rustica) Wing and Tail Feathers.

Pap PL, Osváth G, Aparicio JM, Bărbos L, Matyjasiak P, Rubolini D, Saino N, Vágási CI, Vincze O, Møller AP - PLoS ONE (2015)

Bottom Line: Furthermore, we compared structural properties of Ta6 of barn swallows from six European populations.Ta6 elongation in males resulted in feathers with reduced resistance, as shown by the low barb density and reduced bending stiffness compared to females.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.

View Article: PubMed Central - PubMed

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.

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.

No MeSH data available.


Related in: MedlinePlus

Variation in feather quality traits of Ta6 in male (black) and female (white) barn swallows from six European populations (DK—Denmark, UA—Ukraine, RO—Romania, PL—Poland, IT—Italy, ES—Spain) (mean + SE).
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pone.0130844.g004: Variation in feather quality traits of Ta6 in male (black) and female (white) barn swallows from six European populations (DK—Denmark, UA—Ukraine, RO—Romania, PL—Poland, IT—Italy, ES—Spain) (mean + SE).

Mentions: The length of Ta6 varied significantly among populations. Males had significantly longer outermost tail feathers than females (Table 3, Fig 4A). The significant interaction between population and sex indicated that sexual dimorphism in Ta6 length varied among populations. Rachis diameter was significantly larger in males than in females, and the non-significant sex × population interaction indicated that the difference between males and females in this trait was similar among populations (Table 3, Fig 4B). The significant variation in rachis width between populations was unrelated to sexual dimorphism in tail length, as change in this trait among populations was found not to be associated with sexual dimorphism in Ta6 (Fig 4B). None of the results changed after controlling for the significant and positive effect of feather length on rachis width (β (SE) = 0.16 x 10−2 (0.04 × 10−2), t = 3.67, P = 0.0003; Table 3). Barb density was significantly higher in females than in males, and the non-significant interaction between population and sex indicated that the sexual dimorphism in this trait was similar among populations (Table 3, Fig 4C). A near-significant difference in barb density was found between populations, and the change between populations was unrelated to sexual dimorphism in tail length (Table 3, Fig 4C). None of the results changed after controlling for the significant and negative effect of feather length on barb density (β (SE) = -0.06 (0.01), t = 5.54, P < 0.0001; Table 3). Barbule density was similar between sexes and differed significantly among populations (Table 3, Fig 4D). The change in barbule density among populations was unrelated to sexual dimorphism in tail length (Fig 4D). None of the results changed after controlling for the possible confounding effect of barb density on barbule density (Table 3). Bending stiffness was consistently and significantly larger in females than in males, as indicated by the significant sex effect and the non-significant sex × population interaction (Table 3, Fig 4E). Population significantly explained variation in bending stiffness, although the change was unrelated to sexual dimorphism in tail length (Fig 4E). None of the results was affected by the significant and positive effect of feather length and rachis width on deflection (feather length: β (SE) = 0.05 (0.01), t = 6.22, P < 0.0001; rachis width: β (SE) = 3.11 (1.02), t = 3.04, P = 0.003; Table 3).


Sexual Dimorphism and Population Differences in Structural Properties of Barn Swallow (Hirundo rustica) Wing and Tail Feathers.

Pap PL, Osváth G, Aparicio JM, Bărbos L, Matyjasiak P, Rubolini D, Saino N, Vágási CI, Vincze O, Møller AP - PLoS ONE (2015)

Variation in feather quality traits of Ta6 in male (black) and female (white) barn swallows from six European populations (DK—Denmark, UA—Ukraine, RO—Romania, PL—Poland, IT—Italy, ES—Spain) (mean + SE).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482263&req=5

pone.0130844.g004: Variation in feather quality traits of Ta6 in male (black) and female (white) barn swallows from six European populations (DK—Denmark, UA—Ukraine, RO—Romania, PL—Poland, IT—Italy, ES—Spain) (mean + SE).
Mentions: The length of Ta6 varied significantly among populations. Males had significantly longer outermost tail feathers than females (Table 3, Fig 4A). The significant interaction between population and sex indicated that sexual dimorphism in Ta6 length varied among populations. Rachis diameter was significantly larger in males than in females, and the non-significant sex × population interaction indicated that the difference between males and females in this trait was similar among populations (Table 3, Fig 4B). The significant variation in rachis width between populations was unrelated to sexual dimorphism in tail length, as change in this trait among populations was found not to be associated with sexual dimorphism in Ta6 (Fig 4B). None of the results changed after controlling for the significant and positive effect of feather length on rachis width (β (SE) = 0.16 x 10−2 (0.04 × 10−2), t = 3.67, P = 0.0003; Table 3). Barb density was significantly higher in females than in males, and the non-significant interaction between population and sex indicated that the sexual dimorphism in this trait was similar among populations (Table 3, Fig 4C). A near-significant difference in barb density was found between populations, and the change between populations was unrelated to sexual dimorphism in tail length (Table 3, Fig 4C). None of the results changed after controlling for the significant and negative effect of feather length on barb density (β (SE) = -0.06 (0.01), t = 5.54, P < 0.0001; Table 3). Barbule density was similar between sexes and differed significantly among populations (Table 3, Fig 4D). The change in barbule density among populations was unrelated to sexual dimorphism in tail length (Fig 4D). None of the results changed after controlling for the possible confounding effect of barb density on barbule density (Table 3). Bending stiffness was consistently and significantly larger in females than in males, as indicated by the significant sex effect and the non-significant sex × population interaction (Table 3, Fig 4E). Population significantly explained variation in bending stiffness, although the change was unrelated to sexual dimorphism in tail length (Fig 4E). None of the results was affected by the significant and positive effect of feather length and rachis width on deflection (feather length: β (SE) = 0.05 (0.01), t = 6.22, P < 0.0001; rachis width: β (SE) = 3.11 (1.02), t = 3.04, P = 0.003; Table 3).

Bottom Line: Furthermore, we compared structural properties of Ta6 of barn swallows from six European populations.Ta6 elongation in males resulted in feathers with reduced resistance, as shown by the low barb density and reduced bending stiffness compared to females.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.

View Article: PubMed Central - PubMed

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.

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.

No MeSH data available.


Related in: MedlinePlus