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Ecology and caudal skeletal morphology in birds: the convergent evolution of pygostyle shape in underwater foraging taxa.

Felice RN, O'Connor PM - PLoS ONE (2014)

Bottom Line: The evolution of this function for the tail contributed to the diversification of birds by allowing them to utilize a wider range of flight behaviors and thus exploit a greater range of ecological niches.This study explores whether differences in flight behavior are also associated with variation in caudal vertebra and pygostyle morphology.Thus, distinct locomotor behaviors influence not only feather attributes but also the underlying caudal skeleton, reinforcing the importance of the entire caudal locomotor module in avian ecological diversification.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Ohio University, Athens, Ohio, United States of America ; Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, United States of America.

ABSTRACT
Birds exhibit a specialized tail that serves as an integral part of the flight apparatus, supplementing the role of the wings in facilitating high performance aerial locomotion. The evolution of this function for the tail contributed to the diversification of birds by allowing them to utilize a wider range of flight behaviors and thus exploit a greater range of ecological niches. The shape of the wings and the tail feathers influence the aerodynamic properties of a bird. Accordingly, taxa that habitually utilize different flight behaviors are characterized by different flight apparatus morphologies. This study explores whether differences in flight behavior are also associated with variation in caudal vertebra and pygostyle morphology. Details of the tail skeleton were characterized in 51 Aequornithes and Charadriiformes species. Free caudal vertebral morphology was measured using linear metrics. Variation in pygostyle morphology was characterized using Elliptical Fourier Analysis, a geometric morphometric method for the analysis of outline shapes. Each taxon was categorized based on flight style (flap, flap-glide, dynamic soar, etc.) and foraging style (aerial, terrestrial, plunge dive, etc.). Phylogenetic MANOVAs and Flexible Discriminant Analyses were used to test whether caudal skeletal morphology can be used to predict flight behavior. Foraging style groups differ significantly in pygostyle shape, and pygostyle shape predicts foraging style with less than 4% misclassification error. Four distinct lineages of underwater foraging birds exhibit an elongate, straight pygostyle, whereas aerial and terrestrial birds are characterized by a short, dorsally deflected pygostyle. Convergent evolution of a common pygostyle phenotype in diving birds suggests that this morphology is related to the mechanical demands of using the tail as a rudder during underwater foraging. Thus, distinct locomotor behaviors influence not only feather attributes but also the underlying caudal skeleton, reinforcing the importance of the entire caudal locomotor module in avian ecological diversification.

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5a: Flight Style pFDA Plot: First Caudal Vertebra. Misclassification Rate = 41.18%. 5b: Flight Style pFDA Plot: Middle Free Caudal Vertebra. Misclassification Rate = 37.25%. 5c: Flight Style pFDA Plot: Last Free Caudal Vertebrae. Misclassification Rate = 37.25%.
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pone-0089737-g005: 5a: Flight Style pFDA Plot: First Caudal Vertebra. Misclassification Rate = 41.18%. 5b: Flight Style pFDA Plot: Middle Free Caudal Vertebra. Misclassification Rate = 37.25%. 5c: Flight Style pFDA Plot: Last Free Caudal Vertebrae. Misclassification Rate = 37.25%.

Mentions: To assist with interpreting which specific variables best explain differences among groups, we used pFDA ordinations. Using flight style as the grouping factor, pFDA of each of the three free caudal vertebrae generated a misclassification rate of 37–41% (Fig. 5). The majority of misclassifications occurred between flapping and flap-gliding taxa, in addition to commonly misclassifying both static and dynamic soaring taxa as flappers. In general, only wing-propelled flightless birds (Pygoscelis papua and Pygoscelis adeliae) and one foot-propelled flightless bird (Phalacrocorax harrisi) consistently occupy distinct regions of pFDA morphospace. Pygoscelis is characterized by a dorsoventrally restricted, laterally wide centrum and spinous process and a laterally restricted transverse process. Phalacrocorax harrisi exhibits a large spinous process and a small vertebral centrum. The remaining 48 taxa, representing the flap, flap-glide, static soar, and dynamic soar groups are clustered together in pFDA morphospace and lack any strong discriminating characteristics among the groups.


Ecology and caudal skeletal morphology in birds: the convergent evolution of pygostyle shape in underwater foraging taxa.

Felice RN, O'Connor PM - PLoS ONE (2014)

5a: Flight Style pFDA Plot: First Caudal Vertebra. Misclassification Rate = 41.18%. 5b: Flight Style pFDA Plot: Middle Free Caudal Vertebra. Misclassification Rate = 37.25%. 5c: Flight Style pFDA Plot: Last Free Caudal Vertebrae. Misclassification Rate = 37.25%.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3935938&req=5

pone-0089737-g005: 5a: Flight Style pFDA Plot: First Caudal Vertebra. Misclassification Rate = 41.18%. 5b: Flight Style pFDA Plot: Middle Free Caudal Vertebra. Misclassification Rate = 37.25%. 5c: Flight Style pFDA Plot: Last Free Caudal Vertebrae. Misclassification Rate = 37.25%.
Mentions: To assist with interpreting which specific variables best explain differences among groups, we used pFDA ordinations. Using flight style as the grouping factor, pFDA of each of the three free caudal vertebrae generated a misclassification rate of 37–41% (Fig. 5). The majority of misclassifications occurred between flapping and flap-gliding taxa, in addition to commonly misclassifying both static and dynamic soaring taxa as flappers. In general, only wing-propelled flightless birds (Pygoscelis papua and Pygoscelis adeliae) and one foot-propelled flightless bird (Phalacrocorax harrisi) consistently occupy distinct regions of pFDA morphospace. Pygoscelis is characterized by a dorsoventrally restricted, laterally wide centrum and spinous process and a laterally restricted transverse process. Phalacrocorax harrisi exhibits a large spinous process and a small vertebral centrum. The remaining 48 taxa, representing the flap, flap-glide, static soar, and dynamic soar groups are clustered together in pFDA morphospace and lack any strong discriminating characteristics among the groups.

Bottom Line: The evolution of this function for the tail contributed to the diversification of birds by allowing them to utilize a wider range of flight behaviors and thus exploit a greater range of ecological niches.This study explores whether differences in flight behavior are also associated with variation in caudal vertebra and pygostyle morphology.Thus, distinct locomotor behaviors influence not only feather attributes but also the underlying caudal skeleton, reinforcing the importance of the entire caudal locomotor module in avian ecological diversification.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Ohio University, Athens, Ohio, United States of America ; Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, United States of America.

ABSTRACT
Birds exhibit a specialized tail that serves as an integral part of the flight apparatus, supplementing the role of the wings in facilitating high performance aerial locomotion. The evolution of this function for the tail contributed to the diversification of birds by allowing them to utilize a wider range of flight behaviors and thus exploit a greater range of ecological niches. The shape of the wings and the tail feathers influence the aerodynamic properties of a bird. Accordingly, taxa that habitually utilize different flight behaviors are characterized by different flight apparatus morphologies. This study explores whether differences in flight behavior are also associated with variation in caudal vertebra and pygostyle morphology. Details of the tail skeleton were characterized in 51 Aequornithes and Charadriiformes species. Free caudal vertebral morphology was measured using linear metrics. Variation in pygostyle morphology was characterized using Elliptical Fourier Analysis, a geometric morphometric method for the analysis of outline shapes. Each taxon was categorized based on flight style (flap, flap-glide, dynamic soar, etc.) and foraging style (aerial, terrestrial, plunge dive, etc.). Phylogenetic MANOVAs and Flexible Discriminant Analyses were used to test whether caudal skeletal morphology can be used to predict flight behavior. Foraging style groups differ significantly in pygostyle shape, and pygostyle shape predicts foraging style with less than 4% misclassification error. Four distinct lineages of underwater foraging birds exhibit an elongate, straight pygostyle, whereas aerial and terrestrial birds are characterized by a short, dorsally deflected pygostyle. Convergent evolution of a common pygostyle phenotype in diving birds suggests that this morphology is related to the mechanical demands of using the tail as a rudder during underwater foraging. Thus, distinct locomotor behaviors influence not only feather attributes but also the underlying caudal skeleton, reinforcing the importance of the entire caudal locomotor module in avian ecological diversification.

Show MeSH