Within-taxon phylogeographic structure
Both our SNP and mtDNA datasets contain sufficient genetic insights to
explore phylogeographic trends within the four primary taxa. In addition
to the well-supported dichotomy between KW and KWm,
the SNPs identified a shallow split in KW between Bulloo and Cooper
populations (sites 111–114 versus 115–120; Fig. 3), They also revealed
additional albeit more complicated phylogeographic structure for the
other three taxa (Figs. 3, 4), herein further explored using
taxon-specific PCoAs (Fig. 7).
For KN, there was a primary dichotomy between the three northern and
four southern sites which reflects latitude rather than river basin
membership (Fig. 7a). Most notably, the Burdekin KN were closely allied
with those in the Fitzroy River (Figs. 3, 7) despite being somewhat of a
northern outlier (Fig. 1).
A more complex pattern is evident within KE+. All relevant PCoAs (Figs.
2b, 2d, 4c, S1) consistently found that Condamine fish
(KEm) were genetically most similar to those in the
Burnett, while two geographic outliers (sites 1 and 16) and a number of
regional population clusters were present for pure KE in the RAxML tree
(Fig. 3b). A KE-specific PCoA revealed a similar pattern of diversity,
including the site 1 and 16 outliers (discussed separately), but was
also able to detect a primary phylogeographic split between sites from
the Maroochy River northwards and west to the Burnett (sites 10–29,
excluding site 16) versus sites south of and including the Pine and
Brisbane Rivers (sites 28–48). The northern outlier (site 1, Barron
River) clearly clusters with sites 19–24 (Burrum and Mary Rivers),
supporting its likely status as an introduced population from that part
of KE’s range. Intriguingly, both individuals from site 16 (Burnett
River) are anomalously placed, one intermediate between the two primary
clusters (and showing elevated heterozygosity levels) and the other
clustering with the southern phylogroup. This same pattern is displayed
in the allozyme data (PCoA not shown) and in the mtDNA tree (Fig. S3),
with one individual from site 16 clustering with Brisbane River
haplotypes (southern phylogroup) and the other with Burnett River
haplotypes (northern phylogroup).
With respect to KS, most sites are relatively homogeneous, with only
modest structure relating to geographic outlying populations in two of
the Border Rivers (Severn and McIntyre Rivers; sites 60, 61), the
Macleay River (site 49), and the Shoalhaven River (site 52), the latter
clustering with one of the sites in the adjacent drainage divide (site
83, Murrumbidgee River) and therefore inferring a source population.
Although the mtDNA data are also relatively homogeneous for KS, the
Border Rivers harbored two distinctive cytb lineages at high
frequency that were absent elsewhere in pure KS (Fig. 6).
Discussion Building on the work of Thacker et al. (2007), we present three
comprehensive molecular datasets that together identify four primary
taxa (KN, KE+, KS, and KW+) plus several examples of historic
(KEm, KWm) and relatively recent
admixture (KSxKE) within the parent species H. klunzingeri . All
primary taxa, lineages and admixed zones are fully diagnosable by
numerous independent genetic markers and our intensive sampling provides
an ideal starting point for future field surveys to plug apparent
distributional gaps, ecological assessments of the H. klunzingericomplex, or formal taxonomic revision. Regarding the latter, allocating
the nominal form of H. klunzingeri s.s. (Ogilby, 1898) to a
specific taxon may prove problematic, given the type locality (the
Murray River in South Australia) is apparently, at least the time of
collecting for genetic evaluation, a hybrid zone (KSxKE).