Evolution of male tail characters. Drawings of the male tail in ventral view are shown above the Caenorhabditis phylogeny. The male tail possesses a cuticular fan around the cloaca. Nine pairs of sensory rays are embedded in the fan. Differences between species are found in the shape of the anterior margin and the terminal end of the fan, in the arrangement of the rays and in the shape of the precloacal lip (cf. ). Seven characters of the male tail with two character states each are mapped onto the tree. The mating position is included as an eighth character. The spiral mating position is found only in the Angaria group (C. angaria, C. sp. 12 and C. sp. 8). It is correlated with a particularly narrow fan (compare the images). Male tails are largely identical in all species of the Elegans group, in C. drosophilae and C. sp. 2 and in C. angaria and C. sp. 12.
Kiontke et al. BMC Evolutionary Biology 2011 11:339 doi:10.1186/1471-2148-11-339