Morphological separation of Trochosa robusta (Simon, 1876) and Trochosa ruricola (De Geer, 1778) females (Araneae: Lycosidae)

Within the wolf-spider genus Trochosa (C. L. Koch, 1848), five species occur in Central Europe: T. hispanica Simon, 1870; T. robusta (Simon, 1876); T. ruricola (de Geer, 1778); T. spinipalpis (F. O. P.-Cambridge, 1895); T. terricola Thorell, 1856 (see Hänggi et al., 1995). These five species are very similar in their morphology (size, genitalia) and are thus considered sibling species (Engelhardt, 1964). Separation of the females is particularly difficult and several attempts to distinguish preserved material have been undertaken (e.g. Chrysanthus, 1955; Buchar, 1959; Engelhardt, 1964). On the basis of his comprehensive study, Engelhardt (1964) concluded that the high variability of epigyne and vulva characters makes it impossible to use these organs for an exact differentiation of the species. Engelhardt (1964) regarded body coloration of living specimens, especially in the females, as the only reliable character to distinguish the species. However, in recent determination keys, genital characters are used to separate the Trochosa females to some extent (e.g. Tanaka, 1988; Roberts, 1995). Roberts (1985) pointed out that the “overall impression” of the epigyne structure is more informative than comparison of single parts. The same is true for differences in body morphology. In the present study, we attempt a morphological separation of T. robusta and T. ruricola females using multivariate statistical analyses. We used Principal Components Analysis as a tool to condense interrelated variables into a small number of components that can be used to quantify the “overall impression” mentioned above in terms of size and shape.