The systematics, biogeography and conservation status of species in the freshwater crayfish genus Engaewa Riek (Decapoda: Parastacidae) from south-western Australia

This paper presents a review of the systematics of freshwater crayfish species in the genus Engaewa Riek, endemic to south-western Australia. Allozyme electrophoresis of six allopatric populations of Engaewa and several outgroup taxa at 17 loci was initially used to identify four distinct genetic groups within the genus. Morphological characters were then used to establish within and between species boundaries more precisely. Five species were recognised, comprising the existing species E. subcoerulea Riek, E. reducta Riek, and E. similis Riek, plus two new species, E. pseudoreducta, sp. nov. and E. walpolea, sp. nov. The genus is endemic to south-western Australia where distributions of species conform to those expected for slowly dispersing, inland aquatic organisms wedded to year-round cool and wet conditions. The range of the genus occurs within the Warren Bioregion of Australia. The species occupy well-defined and largely non-overlapping geographical ranges. Within the bioregion, apparent incipient speciation exists in the Cape Naturaliste Cape Leeuwin subregion, confirming a pattern observed for other aquatic organisms. Morphological and electrophoretic evidence suggests that species in the genus are more closely related to each other than they are to other species of extant freshwater crayfish, suggesting that they represent a monophyletic group. Nevertheless, the morphological variation displayed by Engaewa clearly falls within that found for the genus Engaeus Erichson from south-eastern Australia, indicating that a broad-scale generic revision for the entire group would be appropriate. The narrow geographical ranges of E. walpolea, sp. nov., E. pseudoreducta, sp. nov. and E. reducta, coupled with known threats to populations, warrant concern for these species from a conservation viewpoint.