Evolutionary systematics of the Australian Cyzicidae (Crustacea, Branchiopoda, Spinicaudata) with the description of a new genus

Abstract

In Australia's arid and semi-arid zone, most aquatic habitats are nonpermanent. Although approximately 70% of its land surface belongs to these zones, very little is known of the iconic ‘large branchiopods’ that inhabit these important and widespread habitats. In the present study, we investigated 737 Australian specimens of the spinicaudatan taxa Caenestheria and Caenestheriella with a combination of one mitochondrial (cytochrome oxidase subunit I; COI) and three nuclear (elongation factor 1α, internal transcribed spacer 2, and 28S) markers to assess the diversity of species, their phylogenetic relationships, and phylogeographical history. The initial species delimitation was based on COI employing a combination of phylogenetic analyses and two automated approaches to species delimitation (general mixed Yule coalescent model and Automated Barcode Gap Discovery). The outcome was tested by the nuclear markers and considered under differing species concepts. The number of delineated species ranged from 14–27, in no case being in full agreement with any of the two automated approaches. The lower numbers resulted if inferred reproductive isolation, as required for the biological or Hennigian species concept, was employed. Although nuclear markers did not indicate ongoing reproduction, the lack of sympatric co-occurrences inhibited inferences of definitive reproductive isolation in several instances. If monophyly or an ‘independent evolutionary fate’ was employed, as required for the phylogenetic or evolutionary species concepts, the species' distribution was of no importance and up to 27 species could be delimitated. Because the Australian representatives of both studied genera could not be clearly separated from each other but constitute a single monophyletic clade separated from all available non-Australian representatives of these genera, we describe a new spinicaudatan genus Ozestheria gen. nov. to accommodate these species. Populations revealed relatively small levels of genetic differentiation over large areas of central and eastern Australia. By far the most pronounced levels of genetic differentiation were observed towards the north-eastern regions, a pattern possibly explainable by ecological conditions and the movement of nomadic water birds that disperse resting eggs. © 2015 The Linnean Society of London