First molecular data on the Western Australian Diacyclops (Copepoda, Cyclopoida) confirm morpho-species but question size differentiation and monophyly of the Alticola-group

Size differentiation has been considered an important phenomenon in evolution, and in situ speciation was hypothesized in the past for the parapatric subterranean Western Australian <i>Diacyclops</i> Kiefer, 1927 species from the alticola-group, based on morphological evidence. Aims of this study are to: derive their preliminary molecular phylogenies based on mitochondrial (12S) and nuclear (18S) genes; test if morpho-species are supported by molecular data; examine monophyly of the alticola-group; and test whether the size differences evolved in situ after colonization by a single ancestral species or resulted from different phylogeny. Analyses of the 12S sequences reveal at least six well defined clades, each corresponding to one morpho-species. The divergences are very high between all species, suggesting only a remote relationship, with those between sympatric species with significant size difference being in excess of 27%. Surprisingly, all analyses show very high bootstrap values for the clade formed by two cosmopolitan surface-water species, <i>Diacyclops bisetosus</i> (Rehberg, 1880) and <i>D. bicuspidatus</i> (Claus, 1857), despite numerous morphological differences. The 18S dataset also supports only a remote relationship between <i>Diacyclops scanloni</i> Karanovic, 2006 and two other Western Australian members of the alticola-group: <i>D. humphreysi</i> s. str. Pesce & De Laurentiis, 1996 and <i>D. sobeprolatus</i> Karanovic, 2006. Preliminary analyses suggest absence of in situ speciation and parallel evolution in the Western Australian <i>Diacyclops</i>, interspecific size differentiation being a result of different phylogeny. The alticola-group may be polyphyletic, and we recognize morphological characters that define two main lineages. A possibility of cryptic speciation in the cosmopolitan <i>D. bisetosus</i> is also suggested, and several sequences of <i>Diacyclops</i> available from GenBank are recognized either as contamination or misidentification.