Genomic data and morphological re‐assessment reveals synonymy and hybridisation among Seringia taxa (Lasiopetaleae, Malvaceae) in remote north‐western Australia

Abstract

Conservation of rare or threatened species requires a range of information, including a sound taxonomic foundation, to ensure appropriate management. However, rare species are often known from a limited number of specimens, and that can hinder taxonomic understanding. Seringia exastia and S. katatona are two conservation-listed taxa that were poorly known in the remote Kimberley region of northern Western Australia. Recent surveys discovered additional populations of both species but also revealed extensive morphological variation that obscured the boundary between the two species and a third, more widespread species, S. nephrosperma. We applied genomic data (>5000 SNP loci) to investigate species boundaries and hybridisation within this group. We found unequivocal evidence that S. katatona is a hybrid between S. exastia and S. nephrosperma, which is consistent with its intermediate morphology in diagnostic characters between the two highly divergent parents. Unexpectedly, we also uncovered a lack of genome-wide differentiation and polyphyly between S. exastia and an intended outgroup taxon, S. elliptica. These results have significant taxonomic implications, for which reason we present a revised taxonomic treatment that shows S. katatona to be a nothospecies, S. ×katatona, and synonymises S. elliptica under S. exastia, the oldest effectively published name. These taxonomic revisions present new information that will enable reconsideration of the current conservation status of these taxa and inform their management in northern Western Australia.

Revised taxonomy for two species complexes of Western Australian Isopogon (Proteaceae) using RADseq

“…RAD sequencing methods provide thousands of single nucleotide polymorphisms (SNPs) useful for both population genetic and phylogenetic analyses. RAD sequencing approaches have been effectively used to evaluate species boundaries in plant genera, e.g., Diospyros (Linan & al., 2021), Leptospermum (Binks & Byrne, 2022), Rhodanthemum (Wagner & al., 2020), Seringia (Binks & al., 2020), Triodia (Anderson & al., 2017), and Viburnum (Spriggs & al., 2019). There has been concern that the higher resolution provided by genomic data will lead to “taxonomic inflation”, an increase in numbers of species from the recognition of infraspecific structure at the species level (Isaac & al., 2004), and a conservative interpretation of genomic data has been advocated (Coates & al., 2018).…”

“…Some of the techniques used to analyse genomic data, particularly coalescent methods modelling lineage splitting, are known to delimit population structure as well as species‐level differences (Sukumaran & Knowles, 2017). Despite the concern for genomic oversplitting, recent studies using genomic data have sometimes conversely determined that previous morphological taxonomic work had arguably oversplit species (e.g., Georges & al., 2018; Binks & al., 2020; Binks & Byrne, 2022; Wilson & al., 2022). It remains important to interpret genomic results carefully and in an evolutionary context in conjunction with other lines of evidence (see, e.g., Yeates & al., 2011), especially when delimiting species in groups where patterns of evolutionary relationship are complex.…”

Using RADseq to resolve species boundaries in a morphologically complex group of yellow-flowered shrubs (Geleznowia, Rutaceae)

“…& G.Forst. (Binks and Byrne 2022), Rhodanthemum B.H.Wilcox, K.Bremer & Humphries (Wagner et al 2020), Seringia J.Gay (Binks et al 2020), Triodia R.Br. (Anderson et al 2017) and Viburnum L. (Spriggs et al 2019).…”

Morphological and molecular evidence refute a broad circumscription for

“…We then use DArTSeq to capture thousands of genome-wide single-nucleotide polymorphisms (SNPs) to inform fine-scale genetic relationships among individuals. Diversity Arrays Technology generates genome-wide SNP data, which has the capacity to probe population genetic structure, and so identify restrictions in gene flow and reproductive isolation, with a sensitivity beyond any inference possible by using traditional molecular data sources (Melville et al 2017;Binks et al 2020). In this study, we test the broad circumscription proposed for Pultenaea glabra, and the status of each tag-named entity using a combination of morphological and molecular datasets, the latter comprising thousands of SNPs.…”