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Wing bone laminarity is not an adaptation for torsional resistance in bats.

Lee AH, Simons EL - PeerJ (2015)

Bottom Line: Our results show that humeri from bats across a wide phylogenetic and body size range do not contain any laminar bone.Phylogenetically-informed scaling analyses reveal that the difference in vascularity between birds and bats is best explained by higher somatic relative growth rates in birds.The presence of wing bone laminarity in birds and its absence in bats suggests that laminar bone is not a necessary biomechanical feature in flying vertebrates and may be apomorphic to birds.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anatomy, Midwestern University , Glendale, AZ , USA.

ABSTRACT
Torsional loading is a common feature of skeletal biomechanics during vertebrate flight. The importance of resisting torsional loads is best illustrated by the convergence of wing bone structure (e.g., long with thin walls) across extant bats and birds. Whether or not such a convergence occurs at the microstructural level is less clear. In volant birds, the humeri and ulnae often contain abundant laminar bony tissue in which primary circumferential vascular canals course concentrically about the long axis of the bone. These circumferential canals and the matrix surrounding them presumably function to resist the tissue-level shear stress caused by flight-induced torsion. Here, we assess whether or not laminar bone is a general adaptive feature in extant flying vertebrates using a histological analysis of bat bones. We sampled the humeri from six adult taxa representing a broad phylogenetic and body size range (6-1,000 g). Transverse thick sections were prepared from the midshaft of each humerus. Bone tissue was classified based on the predominant orientation of primary vascular canals. Our results show that humeri from bats across a wide phylogenetic and body size range do not contain any laminar bone. Instead, humeri are essentially avascular in bats below about 100 g and are poorly vascularized with occasional longitudinal to slightly radial canals in large bats. In contrast, humeri from birds across a comparable size range (40-1,000 g) are highly vascularized with a wide range in bone laminarity. Phylogenetically-informed scaling analyses reveal that the difference in vascularity between birds and bats is best explained by higher somatic relative growth rates in birds. The presence of wing bone laminarity in birds and its absence in bats suggests that laminar bone is not a necessary biomechanical feature in flying vertebrates and may be apomorphic to birds.

No MeSH data available.


Related in: MedlinePlus

Isometric scaling of polar section modulus (Zp) in humeri of bats and birds.Shaded regions are 95% confidence bands. Representative views of histology from chiropteran ((A) Phalaenoptilus nuttallii, (B) Nothura darwinii, (C) Tinamus major) and avian ((D) Phyllostomus discolor, (E) Rousettus leschenaultii, (F) Pteropus vampyrus) humeri suggest that the vascular dichotomy has little impact on the torsional rigidity of humeri.
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fig-6: Isometric scaling of polar section modulus (Zp) in humeri of bats and birds.Shaded regions are 95% confidence bands. Representative views of histology from chiropteran ((A) Phalaenoptilus nuttallii, (B) Nothura darwinii, (C) Tinamus major) and avian ((D) Phyllostomus discolor, (E) Rousettus leschenaultii, (F) Pteropus vampyrus) humeri suggest that the vascular dichotomy has little impact on the torsional rigidity of humeri.

Mentions: Notwithstanding the vascular dichotomy, humeri in adult bats and birds of comparable size may have similar cross-sectional geometry. Specifically, we are unable to reject the possibility that chiropteran and avian polar section modulus (Zp) scales isometrically with the product of mass and humeral length (Fig. 6). Scaling relationships based on OLS and PGLS regression are indistinguishable (Table 4) probably because the sample size of seven bats and 18 birds is too small for the effects of phylogeny to be significant. Of course, greatly increased sampling may improve detection of differences in how Zp scales with size between chiropteran and avian humeri. There is, however, independent evidence to support the interpretation that some mechanical properties of bat and bird humeri really are similar.


Wing bone laminarity is not an adaptation for torsional resistance in bats.

Lee AH, Simons EL - PeerJ (2015)

Isometric scaling of polar section modulus (Zp) in humeri of bats and birds.Shaded regions are 95% confidence bands. Representative views of histology from chiropteran ((A) Phalaenoptilus nuttallii, (B) Nothura darwinii, (C) Tinamus major) and avian ((D) Phyllostomus discolor, (E) Rousettus leschenaultii, (F) Pteropus vampyrus) humeri suggest that the vascular dichotomy has little impact on the torsional rigidity of humeri.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4359045&req=5

fig-6: Isometric scaling of polar section modulus (Zp) in humeri of bats and birds.Shaded regions are 95% confidence bands. Representative views of histology from chiropteran ((A) Phalaenoptilus nuttallii, (B) Nothura darwinii, (C) Tinamus major) and avian ((D) Phyllostomus discolor, (E) Rousettus leschenaultii, (F) Pteropus vampyrus) humeri suggest that the vascular dichotomy has little impact on the torsional rigidity of humeri.
Mentions: Notwithstanding the vascular dichotomy, humeri in adult bats and birds of comparable size may have similar cross-sectional geometry. Specifically, we are unable to reject the possibility that chiropteran and avian polar section modulus (Zp) scales isometrically with the product of mass and humeral length (Fig. 6). Scaling relationships based on OLS and PGLS regression are indistinguishable (Table 4) probably because the sample size of seven bats and 18 birds is too small for the effects of phylogeny to be significant. Of course, greatly increased sampling may improve detection of differences in how Zp scales with size between chiropteran and avian humeri. There is, however, independent evidence to support the interpretation that some mechanical properties of bat and bird humeri really are similar.

Bottom Line: Our results show that humeri from bats across a wide phylogenetic and body size range do not contain any laminar bone.Phylogenetically-informed scaling analyses reveal that the difference in vascularity between birds and bats is best explained by higher somatic relative growth rates in birds.The presence of wing bone laminarity in birds and its absence in bats suggests that laminar bone is not a necessary biomechanical feature in flying vertebrates and may be apomorphic to birds.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anatomy, Midwestern University , Glendale, AZ , USA.

ABSTRACT
Torsional loading is a common feature of skeletal biomechanics during vertebrate flight. The importance of resisting torsional loads is best illustrated by the convergence of wing bone structure (e.g., long with thin walls) across extant bats and birds. Whether or not such a convergence occurs at the microstructural level is less clear. In volant birds, the humeri and ulnae often contain abundant laminar bony tissue in which primary circumferential vascular canals course concentrically about the long axis of the bone. These circumferential canals and the matrix surrounding them presumably function to resist the tissue-level shear stress caused by flight-induced torsion. Here, we assess whether or not laminar bone is a general adaptive feature in extant flying vertebrates using a histological analysis of bat bones. We sampled the humeri from six adult taxa representing a broad phylogenetic and body size range (6-1,000 g). Transverse thick sections were prepared from the midshaft of each humerus. Bone tissue was classified based on the predominant orientation of primary vascular canals. Our results show that humeri from bats across a wide phylogenetic and body size range do not contain any laminar bone. Instead, humeri are essentially avascular in bats below about 100 g and are poorly vascularized with occasional longitudinal to slightly radial canals in large bats. In contrast, humeri from birds across a comparable size range (40-1,000 g) are highly vascularized with a wide range in bone laminarity. Phylogenetically-informed scaling analyses reveal that the difference in vascularity between birds and bats is best explained by higher somatic relative growth rates in birds. The presence of wing bone laminarity in birds and its absence in bats suggests that laminar bone is not a necessary biomechanical feature in flying vertebrates and may be apomorphic to birds.

No MeSH data available.


Related in: MedlinePlus