Effects of diet on the systematic utility of the tortoise carapace

Abstract

The main character used in identifying species of Chelonia is the carapace. The taxonomy of several terrestrial tortoise genera remains highly disputed, due in part to a limited knowledge of the limits of variation in many populations. For taxa where substantial captive populations are maintained and play an important role in conservation, there is a need to ensure correct identification. The use of the carapace in identification has sometimes been criticised due to potential problems of distortion caused by captive diets. I studied the effects of diet on two species; Testudo ibera and Dipsochelys dussumieri. I confirmed previous findings that low calcium ‐ phosphorus ratios cause scute pyramiding and that extreme calcium deprivation results in metabolic bone disease. However, even though poor diets result in bone resorption, deposition at points of stress and abnormal fusion patterns, they do not compromise the taxonomically useful characters of scute proportions, coloration and depressions and they have no impact on the plastron. Such carapace characters and those of the plastron in particular, remain of value in systematics. My study highlights the need for careful examination of the value of taxonomic characters.