Structural and functional aspects of tail squirting: a unique defense mechanism of Diplodactylus (Reptilia: Gekkonidae)

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Abstract
The structure of a unique caudal gland is described for the first time. Glandular material is secreted and stored in a series of caudal chambers that makes up the bulk of the tail. The glandular secretion is forcibly ejected from each chamber through a middorsal rupture zone in the epidermis. Localized contraction of caudal musculature causes ejection of the defensive secretion.All species of Diplodactylus that were known or suspected to be tail squirters plus representatives from each of four other species groups were examined. The following species of Diplodactylus have caudal glands: D. ciliaris, D. elderi, D. michaelseni, D. spinigerus, D. strophurus, D. taenicauda, and D. williamsi.Regenerated tails of gland-bearing species contain a regenerated caudal gland which is structurally different from the original. Here all evidence of segmentation is lost and there is no series of epidermal rupture zones. A pair of elongated secretion masses is found within paired, elongated caudal chambers.The results of a preliminary bioassay indicated that caudal gland secretion may be unpalatable to potential predators and thereby protects the species of Diplodactylus that are tail squirters. The very sticky nature of the secretion may complement the repellant effects of the odorous constituents.