A project undertaken at the Western Australian Museum, and supervised by Nikolai Tatarnic
Introduction
Formed over 600 million years, Australia’s alpine landscape exhibits high levels of endemism (e.g. ~25% of Australia’s alpine plants are endemic). Though it is the highest bioregion in Australia, due to its extreme age the Australian Alps have been weathered over millennia, with few peaks exceeding 2000 m. For alpine specialists, these peaks are isolated habitat islands, and in species with low dispersal capability, such as flightless insects, the potential for reproductive isolation and speciation is high. The grasshopper genus Kosciuscola currently includes 5 species, all endemic to the Australian Alps. Our recent research has uncovered a hidden diversity of cryptic species within the genus. Preliminary collecting across the Snowy Mountains have revealed a recurring assemblage of 3-4 Kosciuscola species on multiple peaks, but not necessarily the same species. Though they have historically been considered as such, we believe that multiple suites of species exist across the Alpine region, representing multiple speciation events. This natural replication affords us a unique opportunity to look at broad patterns of speciation mediated by vicariance and climatic specialization, and may help us predict how Alpine communities will respond to continuing climate change.
Figure 1. Males of “Kosciuscola tristis” from three different populations: A) Dead Horse Gap, NSW; B) Mt Baw Baw, Victoria; and C) Mt Buffalo, Victoria.
Figure 2. Collecting localities sampled for all Kosciuscola species
Figure 3. Sensitivity analysis of ddRAD contig trees. Branches shown are >95% bootstrap. s= minimum number of populations required to process a locus. As s is relaxed, more SNPs are allowed, and resolution increases. Note that although the proportion of missing data also increases, this does not affect the tree.
Background
The grasshopper genus Kosciuscola is unique in many ways. Firstly, K. tristis is the only species known to exhibit temperature-mediated, reversible colour change (Key & Day 1954). Similarly, K. tristis is also the only species of grasshopper to engage in fierce male-male combat (Umbers et al. 2012). And thirdly, the genus is of considerable ecological interest, as all members are restricted to Australia’s Alpine bioregion, with species segregated along an altitudinal gradient. Across their mainland range, from the peak downwards these species are: K. tristis, K. usitatus, K. cognatus, and K cuneatus, with some sympatry at intermediate elevations. We predicted that these recurring, altitudinally segregated assemblages may harbour several cryptic species, isolated from one another by large, low elevation distances. For example, on Mt Kosciusko we find K. tristis, K. usitatus, K. cognatus, and K cuneatus, while at Mt Buffalo we find a different K. tristis, a different K. cognatus, etc. (Fig. 1). We believe these different assemblages reflect relict populations, which were once contiguous but have since become isolated on alpine habitat islands as the continent warmed and their ranges contracted.
Summary
Using molecular samples collected from populations across the entire range of the genus (56 localities, 66 populations, Fig. 2), we reconstructed the phylogeny of Kosciuscola, assessed the connectivity of sampled populations, and used these data to identify cryptic species. To do this we employed whole mitochondrial genome sequencing for our phylogenetic/species delimitation analyses; and used “double digest Restriction site Associated DNA Sequencing” (ddRAD) techniques to generate thousands of single nucleotide polymorphisms (SNPs) suitable for population level analyses. Upon examining the data, we found that in addition to providing population information, the ddRAD data also proved informative in phylogenetic reconstruction (e.g. Fig. 3).
In summary, we found that each species shows distinct phylogeographic patterns. In all four mainland species, there is limited gene flow between the far northeast and far southwest of the Snowy Mountains. However, within each peak there is substantial gene flow, and generally some gene flow with nearby populations, though several populations are surprisingly genetically isolated despite close geographical proximity. Based on these results combined with morphological analyses, we believe that more species descriptions are warranted: K. tristis is undoubtedly two species, K. cognatus is likely two species, and there are possibly new species in K. usitatus (potentially separating into 3 species) and K. cuneatus (potentially 2 species) as well.