Biology of Aganippine trapdoor spiders (Mygalomorphae: Ctenizidae)

Abstract

A taxonomic revision of the tribe Aganippini (Ctenizidae) is made. The genus Blakistonia Hogg is excluded from the tribe, Gaius Rainbow is synonymized with Anidiops Pocock, and Eucyrtops Pocock is re-instated. The group now consists of the four genera Aganippe Cambridge, Idiosoma Ausserer, Anidiops, and Eucyrtops. The former 23 species of the tribe are reduced to nine, and three new species are described, making a total of 12 valid species. Allotypes of five species, previously known only from one sex, are designated and described. Many characters customarily used in mygalomorph taxonomy are criticized and shown to be inadequate. Observations on the life histories and natural history of the species are recorded. The adaptive function of different burrow and door structures is discussed. Distribution of species in relation to particular habitat types in the general environment is mentioned. Parallel adaptation of a specialized foraging behaviour ("twig-lining", whereby spiders attach twigs to the rim of the burrow in such a way that they are utilized as "feeling lines" when foraging) is recorded for seven species in three genera. Twig-lining appears to be an adaptation to relatively dry habitats where the food supply is less abundant. By this method of foraging, animals increase their area of search for food. A relationship between morphology and behaviour is noted. Certain morphological features, in particular the eyes, are shown to be correlated with burrow structure, including door type, and foraging behaviour. The evolutionary radiation of the tribe is shown to be the result of ecological expansion. Postulated phylogeny of the tribe is outlined. Derivation of the genus Idiosoma from Aganippe is postulated. It is suggested that this has been due to "block" inheritance of several characters (which together have adaptive superiority), and which are assorting independently in other species. These characters, when inherited together, mark the irreversible culmination of the adaptive trend of twig-lining, the initial stages of which are exhibited by the adaptively plastic species of Aganippe and Anidiops.