Data from: The cutaneous lipid composition of bat wing and tail membranes: a case of convergent evolution with birds

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.

哺乳动物与鸟类的水蒸气通透屏障定位于表皮最外层的角质层（stratum corneum, SC）。SC内各类脂质的摩尔占比与分子排布，决定了该屏障的完整性。作为哺乳动物SC中丰度最高的脂质类别，神经酰胺的碳链延长与极性增强可促进脂质更紧密的堆砌，进而降低皮肤蒸发失水（cutaneous evaporative water loss, CEWL）。但脂质堆砌过于紧密也会降低SC的水合程度，使其质地变脆；而过高的水合程度则会软化皮肤，却以提升CEWL为代价。脑苷脂不存在于哺乳动物的SC中；其病理性积累会引发戈谢病，导致CEWL大幅升高。不过，脑苷脂却是鸟类SC中的正常组分。我们提出如下假说：蝙蝠的SC中同样存在脑苷脂，因为这类脂质或许对赋予皮肤柔韧性必不可少——而飞行正需要皮肤具备这一特性。我们对4种同域蝙蝠物种的SC脂质组成进行了检测，结果发现与鸟类一致，蝙蝠的SC中含有大量脑苷脂，且未伴随病理状态，这表明蝙蝠与鸟类之间存在趋同演化现象。