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. 2016 Jun 29;283(1833):20160636.
doi: 10.1098/rspb.2016.0636.

The Cutaneous Lipid Composition of Bat Wing and Tail Membranes: A Case of Convergent Evolution With Birds

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Free PMC article

The Cutaneous Lipid Composition of Bat Wing and Tail Membranes: A Case of Convergent Evolution With Birds

Miriam Ben-Hamo et al. Proc Biol Sci. .
Free PMC article

Abstract

The water vapour permeability barrier of mammals and birds resides in the stratum corneum (SC), the outermost layer of the epidermis. The molar ratio and molecular arrangement of lipid classes in the SC determine the integrity of this barrier. Increased chain length and polarity of ceramides, the most abundant lipid class in mammalian SC, contribute to tighter packing and thus to reduced cutaneous evaporative water loss (CEWL). However, tighter lipid packing also causes low SC hydration, making it brittle, whereas high hydration softens the skin at the cost of increasing CEWL. Cerebrosides are not present in the mammalian SC; their pathological accumulation occurs in Gaucher's disease, which leads to a dramatic increase in CEWL. However, cerebrosides occur normally in the SC of birds. We tested the hypothesis that cerebrosides are also present in the SC of bats, because they are probably necessary to confer pliability to the skin, a quality needed for flight. We examined the SC lipid composition of four sympatric bat species and found that, as in birds, their SC has substantial cerebroside contents, not associated with a pathological state, indicating convergent evolution between bats and birds.

Keywords: Aves; Chiroptera; skin.

Figures

Figure 1.
Figure 1.
Principal component analysis based on the weighted fractions of sphingolipids in the wing and tail stratum corneum of bats. (a) Scores for Plecotus christii (filled triangles) and Eptesicus bottae (filled circles), the species found in arid and semi-arid habitats; scores for Pipistrellus kuhlii (open circles), the species found in both mesic and arid habitats in association with human settlements; and scores for Otonycteris hemprichii (open triangles), the species that inhabits hot, dry desert areas. (b) Loading, i.e. the weight relative to the principal components, for each sphingolipid. Non-hydroxy ester-linked fatty acid (N), α-hydroxy ester-linked fatty acid (A), ω-hydroxy ester-linked fatty acid (EO), sphingosine (S), phytosphingosine (P), 6-hydroxysphigosine (H), dehydrosphingosine (DS) and unknown (UK). The scores on the first principal component (PC1) denote decreasing polarity and the scores on the second principal component (PC2) denote increasing chain length.
Figure 2.
Figure 2.
The relationship between residuals calculated from regressing surface area-specific cutaneous water loss against the torpor index of the bats and (a) the scores on the first principal component (PC1) denoting decreasing stratum corneum (SC) sphingolipid polarity, (b) the scores on the second principal component (PC2) denoting increasing (SC) sphingolipid chain length and (c) the scores on the third principal component (PC3). Plecotus christii (filled triangles) and Eptesicus bottae (filled circles) are the species found in arid and semi-arid habitats; Pipistrellus kuhlii (open circles) is the species found in both mesic and arid habitats in association with human settlements and Otonycteris hemprichii (open traingles) is the species that inhabits only hot, dry desert areas.

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