Introduction
Phylogeographic assessments of freshwater fishes have commonly revealed
cryptic species (e.g., Baumsteiger, Kinziger & Aquilar, 2012; Adams et
al., 2014; Pinacho-Pinacho et al., 2018), thereby improving knowledge of
species richness and diversity in aquatic ecosystems globally (Seehausen
& Wagner, 2014). In Australia, for example, the number of recognised
(but not necessarily described) species increased by 39 between 2002 and
2013 (Allen, Midgley & Allen, 2002; Unmack, 2013), with many of the
newly-defined species revealed by molecular phylogenetic and
phylogeographic evidence (Adams et al. 2023). Furthermore,
phylogeographic studies have indicated that historical, geological,
and/or climatic processes can be determinants of contemporary patterns
of biodiversity and distribution across riverine landscapes (e.g.,
Buckley et al., 2021; Shelley et al., 2020; Waters, Burridge & Craw,
2020). Consequently, the phylogeographic assessment of freshwater fishes
provides foundational diversity and biogeographic knowledge upon which
valid ecological and environmental management studies are dependent
(Page et al., 2017).
In this study, we present a molecular phylogeographic assessment of the
western carp gudgeon (Eleotridae: Hypseleotris klunzingeri )
throughout its entire Australian range. This small-bodied freshwater
fish (approximate maximum size is 60 mm TL) is one of the most abundant
and widely-distributed species in eastern Australia (Unmack, 2000;
Pusey, Kennard & Arthington, 2004). Here it occurs as a disjunct
northern population in the Burdekin Basin in central-northern
Queensland, then in coastal drainages from just north of the Fitzroy
Basin to the Clarence Basin, as three disjunct southern populations in
the Macleay, Hunter and Shoalhaven basins in central New South Wales,
inland throughout the Murray-Darling Basin (MDB), and finally west to
the Bulloo River and Cooper Creek in the Lake Eyre Basin (Fig. 1;
Table1). Hypseleotris klunzingeri is often found in sympatry with
other carp gudgeons, all belonging to a species complex comprising a
suite of other sexual and hemi-clonal congeners, but is reproductively
isolated from them (Bertozzi, Adams & Walker, 2000; Schmidt et al.,
2011; Unmack et al., 2019).
As reviewed by Pusey et al. (2004), H. klunzingeri occurs in a
wide range of lotic and lentic habitats, with aquatic plants and
leaf-litter beds, and slow-flowing water (i.e. <0.2 m/s) the
preferred (but not exclusively used) habitat features. The species is
primarily benthic, with a diet dominated by microcrustaceans and
macroinvertebrates (e.g., chironomids, ephemeropterans and
trichotperans). Hypseleotris klunzingeri has a wide range of
water quality tolerances but is only known from upper estuarine areas
downstream of tidal barrages that prevent upstream movement, indicating
that estuarine habitats are not naturally used by the species. Spawning
can occur most of the year (excluding winter), but peaks in spring and
early summer in response to increasing water temperature and daylight
length, and possibly flow events, with flow events reported to catalyse
the onset of mass migration of H. klunzingeri (Pusey et al.,
2004).
As with many other Australian freshwater fishes, the taxonomy and
distribution of H. klunzingeri has historically been equivocal,
having first been mistaken by Klunzinger (1872, 1880) as H.
cyprinoides (which does not occur in Australia), then described asCarrassiops klunzingeri by Ogilby (1898), to be later reassigned
to the genus Hypseleotris . Its common name of western carp
gudgeon relates to the early thought that the taxon primarily occurred
west of the Great Dividing Range compared with the more easterlyH. galii (e.g., Anderson, Lake & Mackay, 1971), whereas today we
know that representatives of both lineages naturally occur both east and
west of the Great Dividing Range (Thacker, Geiger & Unmack, 2022a).
While the current nomenclature suggests a robust taxonomic status,
matrilineal phylogeographic data presented by Thacker et al. (2007)
indicated several divergent lineages within H. klunzingeri that
to date have not been closely re-assessed. Furthermore, their
phylogeographic analyses suggest the low elevation divide between the
coastal Burnett River and the Condamine River in the northern MDB is the
pathway by which H. klunzingeri was exchanged between these
basins (see also Unmack, 2013).
The purpose of this study is to present a thorough molecular
phylogeographic assessment of H. klunzingeri , using comprehensive
sampling and an expanded suite of molecular datasets. Regarding the
latter, our choice of two independent sets of co-dominant nuclear
markers (single nucleotide polymorphisms [SNPs] and allozyme loci),
plus matrilineal sequence data (the mtDNA gene Cytochrome b[cytb ]), ensures that this study is ideally placed to help
resolve the above-described taxonomic uncertainty and re-evaluate
biogeographic patterns in this prominent Australian freshwater fish.