Conclusions
This study has revealed that carp gudgeons are even more speciose than
previously thought, adding several additional candidates to the existing
six sexual species plus their various hemiclonal relatives (Unmack et
al., 2019; Thacker et al., 2022a; Thacker et al., 2022b). Even ignoring
the complication of sympatric hemiclones, many river basins contain at
least three or more sexual species, with the geographically-extensive
MDB notably harboring six sexual taxa (plus multiple hemiclones).
Moreover, the observed partial mismatch between geographic and
phylogenetic patterns, plus the presence of a natural hybrid zone in the
lower Murray and in at least two Darling tributaries add yet more layers
of complication. Given such complexity, future taxonomic and field
identification efforts will be particularly challenging, and ideally
require the involvement of a molecular identification technology (with
SNPs providing the gold standard of unequivocal identification all
sexual and unisexual forms) as part of a coordinated accumulation of
companion morphological exemplars of each morphotype at each site
surveyed. Our own research group has already adopted this strategy where
resources permit.
The dynamic boom and bust nature of many Australian freshwater
ecosystems highlights the need for monitoring spatial genetic patterns
for all resident species over time, particularly after major climate
events such as have impacted eastern Australia over the past decade
(Hughes, Schmidt & Finn, 2009; Lintermans, 2013; Legge et al., 2022).
Our study provides future researchers with a framework to pursue such an
endeavor for the Hypseleotris of eastern Australia. As a major
component of the biodiversity and ecology of these ecosystems, carp
gudgeons also offer great potential for environmental monitoring,
provided researchers can identify individuals to their correct taxon. In
the past carp gudgeons have often been lumped into one composite ‘taxon’
(Hypseleotris spp.) when included in ecological surveys
(Lintermans, 2007), a custom that precludes any genuine assessment of
whether Hypseleotris alpha diversity has declined or shifted
(e.g. hemiclone ratio/presence) at such sites. Finally, this study
further underlines the point that active conservation and management
practices for freshwater fishes, including both the intended (i.e.,
wrong genetic lineage used) and unintended (i.e., where carp gudgeons or
other non-target species unknowingly contaminate the hatchery release
event) consequences of fish stocking programs (Lintermans, 2004), need
to be mindful of the existence of both undescribed candidate species,
and deep phylogeographic structure within all species, to avoid
undertaking or facilitating translocations or mixing of distinct genetic
lineages.