Highly localised morphological diversity in the mayfly <i>Cloeon tasmaniae</i> Tillyard (Ephemeroptera; Baetidae), and a new synonomy with <i>C. paradieniense</i> Suter

Abstract Ambiguity over the features that differentiate two nominal species of baetid mayflies, Cloeon paradieniense Suter and C. tasmaniae Tillyard, in southeast Australia led to a detailed analysis of the morphology and meristics of specimens from Victoria, South Australia and, in particular, Tasmania, where both species have been reported. The data indicate a broad overlap in almost all features between the two taxa, suggesting they are synonymous (also supported by an analysis of CO1 sequences), but also diverse, with highly localised differences among sites, even on the scale of 10s of kilometres and within drainages, despite the broad distribution of the species, slight genetic differences between mainland and Tasmanian specimens, and evidence of significant aerial dispersal capability. We speculate that the localisation reflects gene pools at each site that are much smaller than expected due to some combination of temporally patchy recruitment within long reproductive seasons, strong founder effects in ephemeral habitats, dispersal and mortality schedules that differ with female reproductive strategies, and inbreeding due to facultative parthenogenesis. On the basis of their overlapping morphology and genetics, C. paradieniense is recognised as a junior synonym of C. tasmaniae .