Salivary gland adaptations: modification of the glands for novel uses

Salivary glands across the animal kingdom show a huge array of shapes, sizes and variations in number within the oral cavity. Some are branched, others elongated and unbranched, some are small and numerous, while others are greatly enlarged. In most species the salivary glands are used to produce saliva, which lubricates the oral cavity, aids digestion and protects the oral mucosa and dentition. In some species, however, the glands have been modified so that they function in new and diverse ways. Examples include the ability to create thread from the salivary glands to create hides and cocoons, as shown by some arthropods, the ability to create nests out of saliva, as shown by the Aerodramus swiftlets, or the ability to produce venom from modified salivary glands. In this chapter these different adaptations will be discussed, looking at how the salivary glands have become adapted to their new role, with insights from developmental biology and evolution.