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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 P1, Ta5 and Ta6 in male (black) and female (white) barn swallows from the Romanian population (mean + SE).Figures in the left column are from the models without confounding variables included, while figures from the right column are from models with confounding variables included. For details, see Materials and methods. Significance level for the difference between sexes for each feather type is shown above bars.
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pone.0130844.g002: Variation in feather quality traits of P1, Ta5 and Ta6 in male (black) and female (white) barn swallows from the Romanian population (mean + SE).Figures in the left column are from the models without confounding variables included, while figures from the right column are from models with confounding variables included. For details, see Materials and methods. Significance level for the difference between sexes for each feather type is shown above bars.

Mentions: Feather length differed significantly between feather types and sexes, and the significant sex × feather type interaction indicates that the difference between sexes was non-significant for P1 and Ta5, while Ta6 was significantly longer in males than in females (Table 1, Fig 1). Rachis diameter differed significantly between feather types and was the largest for Ta6, intermediate for P1 and the smallest for Ta5 (Table 1, Fig 2A). Rachis diameter was larger in males than in females for all feathers, as indicated by the significant effect of sex and the non-significant sex × feather type interaction (Table 1, Fig 2A). After accounting for the covariation between rachis width and feather length (β (SE) = 0.01 (0.002), t = 3.99, P = 0.0047), the difference between feather types remained significant (Table 1), although the significant difference between the sexes disappeared. The sex × feather type interaction became significant showing that residual rachis diameter of males was larger than that of females for Ta6, while no significant differences were observed for P1 and Ta5 (Table 1, Fig 2B). Barb density differed significantly between feather types, and was highest for P1, followed by Ta5 and Ta6 (Table 1, Fig 2C). Barb density was higher in females than in males for all feather types, and the difference between sexes was the largest in Ta6 as compared to P1 and Ta5, as indicated by the significant sex × feather type interaction (Table 1, Fig 2C). After including feather length in the model to control its significant and negative relationship with barb density (β (SE) = -0.07 (0.01), t = 5.69, P < 0.0001), the difference between feather types remained significant, with the highest value for P1 (Table 1, Fig 2D). However, the significant difference between sexes disappeared for all feather types, as indicated by the non-significant sex and sex × feather type interaction (Table 1, Fig 2D). Barbule density differed significantly between feather types, and was the highest for P1, followed by Ta6 and Ta5 (Table 1, Fig 2E). Barbule density was similar in the two sexes as indicated by the non-significant effect of sex and sex × feather type interaction (Table 1, Fig 2E). Including in the model barb density as a possible confounding variable of barbule density (β (SE) = -0.26 (0.15), t = 1.76, P = 0.50), the difference between feather types and sexes remained unchanged (Table 1, Fig 2F). Bending stiffness significantly differed between feather types, and was the lowest for Ta6, followed by Ta5 and P1 (Table 1, Fig 2G). Deflection of feathers was significantly higher in males than in females, and the significant sex × feather type interaction indicated that the difference between sexes increased from P1 and Ta5 to Ta6 (Table 1, Fig 2G). After including feather length and rachis width to control their significant and positive effect on deflection (feather length: β (SE) = 0.05 (0.04), t = 1.35, P < 0.0001; rachis width: β (SE) = 4.84 (2.45), t = 1.98, P = 0.0090), the difference between feather types remained significant (Table 1, Fig 1H). However, the difference between sexes decreased and turned to be similar for each feather type, as indicated by the non-significant sex and sex × feather type interaction (Table 1, Fig 1H).


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 P1, Ta5 and Ta6 in male (black) and female (white) barn swallows from the Romanian population (mean + SE).Figures in the left column are from the models without confounding variables included, while figures from the right column are from models with confounding variables included. For details, see Materials and methods. Significance level for the difference between sexes for each feather type is shown above bars.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130844.g002: Variation in feather quality traits of P1, Ta5 and Ta6 in male (black) and female (white) barn swallows from the Romanian population (mean + SE).Figures in the left column are from the models without confounding variables included, while figures from the right column are from models with confounding variables included. For details, see Materials and methods. Significance level for the difference between sexes for each feather type is shown above bars.
Mentions: Feather length differed significantly between feather types and sexes, and the significant sex × feather type interaction indicates that the difference between sexes was non-significant for P1 and Ta5, while Ta6 was significantly longer in males than in females (Table 1, Fig 1). Rachis diameter differed significantly between feather types and was the largest for Ta6, intermediate for P1 and the smallest for Ta5 (Table 1, Fig 2A). Rachis diameter was larger in males than in females for all feathers, as indicated by the significant effect of sex and the non-significant sex × feather type interaction (Table 1, Fig 2A). After accounting for the covariation between rachis width and feather length (β (SE) = 0.01 (0.002), t = 3.99, P = 0.0047), the difference between feather types remained significant (Table 1), although the significant difference between the sexes disappeared. The sex × feather type interaction became significant showing that residual rachis diameter of males was larger than that of females for Ta6, while no significant differences were observed for P1 and Ta5 (Table 1, Fig 2B). Barb density differed significantly between feather types, and was highest for P1, followed by Ta5 and Ta6 (Table 1, Fig 2C). Barb density was higher in females than in males for all feather types, and the difference between sexes was the largest in Ta6 as compared to P1 and Ta5, as indicated by the significant sex × feather type interaction (Table 1, Fig 2C). After including feather length in the model to control its significant and negative relationship with barb density (β (SE) = -0.07 (0.01), t = 5.69, P < 0.0001), the difference between feather types remained significant, with the highest value for P1 (Table 1, Fig 2D). However, the significant difference between sexes disappeared for all feather types, as indicated by the non-significant sex and sex × feather type interaction (Table 1, Fig 2D). Barbule density differed significantly between feather types, and was the highest for P1, followed by Ta6 and Ta5 (Table 1, Fig 2E). Barbule density was similar in the two sexes as indicated by the non-significant effect of sex and sex × feather type interaction (Table 1, Fig 2E). Including in the model barb density as a possible confounding variable of barbule density (β (SE) = -0.26 (0.15), t = 1.76, P = 0.50), the difference between feather types and sexes remained unchanged (Table 1, Fig 2F). Bending stiffness significantly differed between feather types, and was the lowest for Ta6, followed by Ta5 and P1 (Table 1, Fig 2G). Deflection of feathers was significantly higher in males than in females, and the significant sex × feather type interaction indicated that the difference between sexes increased from P1 and Ta5 to Ta6 (Table 1, Fig 2G). After including feather length and rachis width to control their significant and positive effect on deflection (feather length: β (SE) = 0.05 (0.04), t = 1.35, P < 0.0001; rachis width: β (SE) = 4.84 (2.45), t = 1.98, P = 0.0090), the difference between feather types remained significant (Table 1, Fig 1H). However, the difference between sexes decreased and turned to be similar for each feather type, as indicated by the non-significant sex and sex × feather type interaction (Table 1, Fig 1H).

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