Phylogenetic relationships and biogeography of the groundwater-dwelling amphipod genus Pseudoniphargus (Crustacea), with emphasis on the Iberian species

Numerical phylogenetic methods are applied in order to arrive at synapomorphic similarities between species of the stygobiont amphipod genus Pseudoniphargus. Character polarity is assessed by comparison with the relevant outgroups Parapseudoniphargus and Allomelita, within a cluster of presumedly interrelated genera of Hadzioidea. The degree of morphological differentiation of Pseudoniphargus is low and the available potential apomorphies are insufficient to resolve phylogenetic relationships to the species level. The inconsistency in the data is high, which may be a result of an underlying peripatric speciation model, difficulties in discriminating mutual exclusive and homologous character states, and a high probability of independent character evolution. Problems of phylogeny reconstruction at low taxonomic levels are universal. Accidental problems in the case of a stygobiont group are caused by troglomorphism, structural reduction, and senescent morphology. The results of the study lead to the recognition of four well-corroborated monophyletic groups; three consist of sister species only. Remaining taxa are ungrouped or belong to groups which do not emerge after all numerical approaches. The monophyletic groups of Pseudoniphargus are for the greater part geographically coherent and confined either to the Cantabrian Mountains, or to the Lusitanian-Atlantic region, or to the Betic Cordillera. The possible origin of Pseudoniphargus from a thalassostygobiont progenitor which arose in the eastern Atlantic part of the shallow Tethys sea is discussed.