ASELLUS AQUATICUSINFERNUS, NEW SUBSPECIES (ISOPODA: ASELLOTA: ASELLIDAE), FROM ROMANIAN HYPOGEAN WATERS

Abstract

A new, troglomorphic subspecies of Asellus aquaticus, A. a. infernus, from Romania, is described and illustrated. The general architecture of the copulatory appendages, studied with SEM in Romanian and Slovenian hypogean and epigean populations, is compared and discussed. A difference in brood size was determined between Romanian hypogean and epigean populations. Extensive analysis of the data using multivariate discriminant function analysis (DFA) allowed the elucidation of racial differentiation patterns in A. aquaticus from Romania and Slovenia. The number of the initially measured morphometric characters was greatly reduced as the contribution of each character to each discriminant function was assessed. DFA divided the sample complex into distinct epigean-A. a. aquaticus, and hypogean forms-A. a. infernus (Romania) and A. a. cavernicolus (Slovenia). The size of pleopod V and its area as well as the isometric (short distal rami) uropod represent the most important discriminant characters. Distinct separation of Romanian and Slovenian cave populations, i.e., the low degree of convergent evolution toward troglomorphism, might be at least to some extent explained by a different origin of populations and by the considerable ecological differences between both habitats. Asellus (Asellus) aquaticus (L., 1758) is an extreme eurytopic, eurythermal, and expansive species, represented not only in surface waters, but also in all types of hypogean fresh-water systems (Henry et al., 1996). In many localities all over Europe, populations with more or less depigmented specimens are present. However, only some races from Slovenia (Sket, 1965) and Romania (Negoescu, 1989) show further adaptive changes: reduced body pigmentation and depigmented or even degenerated eyes (Sket, 1994; Turk