Trouble at the top? Restricted distribution and extreme population isolation in an alpine crustacean assemblage with unexpected lineage diversity

Abstract

Summary The fragile alpine freshwater ecosystems of Australia are threatened by historic land use and projected climate change, yet little is known about the fauna of these environments. The aim of this study was to analyse the phylogeography of two important components of this ecosystem, an amphipod (Neoniphargus) and an isopod (Coluboltelson), to determine the potential impacts of environmental change on these crustaceans. DNA sequences were generated for the mitochondrial cytochrome c oxidase subunit I (COI) and nuclear 28S ribosomal RNA (28S) of 229 amphipods and 153 isopods from 19 sites across seven creeks in the Bogong High Plains, Victoria, Australia. Phylogenetic analyses were undertaken to define evolutionary significant units (ESUs), and population genetic structure was examined. Analyses of both markers found deep divergences in both taxa, leading to the definition of six amphipod and two isopod ESUs, within both Neoniphargus and Colubotelson. The majority of amphipod ESUs exhibited highly restricted distributions, with essentially no gene flow between sites, even within the same creeks, consistent with the Death Valley Model of population connectivity. By contrast, both isopod ESUs had overlapping distributions across the entire sample area and exhibited some highly limited population connectivity among sites in adjacent headwaters, consistent with the Headwater Model. This study suggests that there is a high level of undiscovered biodiversity within Australian alpine aquatic invertebrates. The highly limited population structure, and restricted distributions have important consequences for the conservation of the headwaters of Australia's largest river system. These findings indicate that habitat loss and/or fragmentation associated with environmental change will result in biodiversity reductions, with species unlikely to shift their ranges in response to future climate change, or recover rapidly from localised extinction events.

Spatial patterns of genetic diversity among Australian alpine flora communities revealed by comparative phylogenomics

“…This suggests that rates of gene flow might be lower in these species compared with other plants. Similarly, genetic structuring among summits within regions has been reported for ground dwelling and flightless terrestrial invertebrate taxa (Endo et al., ), and obligate freshwater invertebrates (Hatley & Murphy, ). Rates of gene flow are also expected to be lower in such taxa compared with most plant species included in this study.…”

“…() used mitochondrial markers to estimate that the isolation of invertebrate communities from summits likely dates back to the early Pleistocene. Patterns of genetic structure described here, and at an even finer scale in animals (Endo et al., ; Hatley & Murphy, ; Mitrovski et al., ), differ from Northern Hemisphere alpine systems where shallow genetic differentiation is typically observed among populations, owing to a history of post‐glacial expansion (Rovito, ; Schoville, Roderick, & Kavanaugh, ; Schoville, Stuckey, & Roderick, ; Shafer, Côté, & Coltman, ; Tribsch & Schönswetter, ).…”

“…Genetic analyses of Australian alpine fauna indicate high levels of genetic structuring at fine spatial scales, with evidence of deep lineage splits among summit communities, including those connected by high‐elevation plateaus (Chapple, Keogh, & Hutchinson, ; Endo et al., ; Hatley & Murphy, ; Koumoundouros, Sumner, Clemann, & Stuart‐Fox, ; Mitrovski, Heinze, Broome, Hoffmann, & Weeks, ; Osborne, Norman, Christidis, & Murray, ). These patterns differ markedly from Northern Hemisphere alpine systems, where shallow genetic differentiation is typically observed among populations owing to a history of post‐glacial expansion (e.g., Buckley, Simon, Shimodaira, & Chambers, ; Ikeda, Senni, Fujii, & Setoguchi, ; Kubow, Robinson, Shama, & Jokela, ; Todisco et al., ).…”

Substantial differences in genetic diversity and spatial structuring among (cryptic) amphipod species in a mountainous river basin

“…Also, we further discriminated the G. pulex morphospecies complex into clade B and clade D. The latter taxon was widespread in the RMO, while the former taxon only occurred at two sites and never in sympatry with clade D. It may not be surprising that our integrative bioassessment revealed additional amphipod species, as this is a common finding especially for mountainous areas (see e.g. Copilaş‐Ciocianu et al, 2019; Hatley & Murphy, 2016; Katouzian et al., 2016; Murphy, Adams, & Austin, 2009; Weiss et al., 2014; Witt, Threloff, & Hebert, 2006). However, from a conservation perspective, the discovery of a new amphipod clade for central Germany attracts particular attention.…”

“…Based on 228 high quality‐filtered genomic ddRAD‐loci, Oeser (2016) identified populations of G. pulex clade E in the near‐natural upstream sections of the Boye to be frequently connected genetically with surrounding populations in the adjacent Lippe catchment. Another example comes from Hatley and Murphey (2016), who revealed that populations of alpine amphipod species situated in headwaters of different catchments in the Bogong High Plains (Australia) are sometimes genetically more closely related than populations within catchments. However, it remains unknown how amphipods actually overcome these ecological and physical boundaries; this represents an interesting topic for future research.…”