Evidence for multiple refugia and hotspots of genetic diversity for Westralunio carteri, a threatened freshwater mussel in south‐western Australia

Abstract

Intraspecific genetic diversity provides the evolutionary potential to adapt to changing environments and ‘hotspots’ of high intraspecific diversity are recognized as key targets for conservation. In south‐western Australia, intraspecific genetic diversity for mesic taxa is not uniformly distributed. Many species comprise highly divergent lineages with unique haplotypes resulting from contraction to refugia during historical arid cycles. Sampling strategies in studies of the region’s unique and ancient freshwater fauna have often focused on broad distributional range, making it difficult to determine boundaries between lineages and the location of genetic hotspots. This study explored the spatial distribution of intraspecific genetic diversity in the threatened freshwater mussel, Westralunio carteri. Mitochondrial DNA sequences for 164 specimens, sampled from all basins within the distribution of the species, were used to describe lineage boundaries and the location of hotspots, and to reconstruct historical demographics. There was strong evidence for three subregions of genetic diversity based on the largely non‐overlapping distributions of three evolutionarily significant units. Spatial and demographic analyses suggest that these evolutionarily significant units persisted through past arid cycles in separate refugia. The majority of haplotypes were unique to a single location, indicating limited connectivity among populations in recent times. Hotspots were identified throughout the region. Most notably, a significant hotspot in the south‐western corner probably arose through the overlap of lineages in historical refugia. Conservation assessments often focus on the species as a whole, even though sublineages, hotspots and the threats faced are not evenly distributed across the species range. This paper highlights that effective conservation of spatially structured taxa requires targeted management of multiple genetic units. Given the importance of formal taxonomic description for conservation listings, further investigation of the potential for species delimitation within W. carteri is required.

A riverine biodiversity hotspot in northern Myanmar supports three new and narrowly endemic freshwater mussel species

“…the Chindwin and the upper Ayeyarwady). Moreover, the two basins may represent hidden ‘hotspots’ of high intraspecific diversity for widespread species, as shown recently for Westralunio carteri Iredale, 1934 in Australia (Benson et al, 2022).…”

Integrated taxonomy reveals new threatened freshwater mussels (Bivalvia: Hyriidae: Westralunio) from southwestern Australia

“…Two recent studies have investigated phylogeographic structuring and the existence of Evolutionary Significant Units (ESUs) and Molecular Operational Taxonomic Units’ (MOTUs) in W. carteri 27 , 28 . Klunzinger et al 27 applied four species delimitation models based on 46 COI mtDNA sequences spanning 13 populations of W. carteri, which revealed unanimous support for at least two MOTUs: “ W. carteri ” I from west coast drainages and “ W. carteri ” II + III from drainages of the south coast lower southwest of southwestern Australia.…”

“…The authors recommended further research was required to better characterise the observed differentiation among lineages and their distribution. Subsequent work by Benson et al 28 incorporated COI and 16S sequences from an additional 119 individuals from 19 populations previously unsampled and showed that the distribution of the two primary lineages rarely overlapped, and that the third lineage appeared to be restricted to just two river systems.…”

Population structure and microhabitat preference of a threatened freshwater mussel, Westralunio carteri, in south-western Australia

“…Recent work has identified the occurrence of two distinct, geographically separated lineages (and putative new species) within the range of the currently described W. carteri (Klunzinger et al, 2021;Benson et al, 2022). This study was conducted in the range of the lineage "W. carteri" I of Klunzinger et al (2021), which is found on the west coast of south-western Australia.…”

“…Westralunio carteri Iredale, 1934 (Hyriidae) is endemic to south-western Australia. It is the only freshwater mussel species currently described from the region, although recent molecular studies have identified distinct, spatially structured genetic lineages and highlighted the need for a taxonomic revision (Klunzinger et al, 2021;Benson et al, 2022). Westralunio carteri (sensu lato) is found only in the South-west Coast Drainage Division of Western Australia, being largely restricted to lotic and lentic systems in forested areas within 100 km of the coast (Klunzinger et al, 2015).…”