Significant genetic structure despite high vagility revealed through mitochondrial phylogeography of an Australian freshwater turtle (Chelodina longicollis)

Abstract

Restriction to the freshwater environment plays a dominant role in the population genetic structure of freshwater fauna. In taxa with adaptations for terrestriality, however, the restrictions on dispersal imposed by drainage divides may be overcome. We investigate the mitochondrial phylogeographic structure of the eastern long-necked turtle (Chelodina longicollis), a widespread Australian freshwater obligate with strong overland dispersa\l capacity and specific adaptations to terrestriality. We predict that such characteristics make this freshwater species a strong candidate to test how life-history traits can drive gene flow and interbasin connectivity, overriding the constraining effects imposed by hydrological boundaries. Contrary to expectations, and similar to low-vagility freshwater vertebrates, we found two ancient mitochondrial haplogroups with clear east-west geographic partitioning either side of the Great Dividing Range. Each haplogroup is characterised by complex genetic structure, demographically stable subpopulations, and signals of isolation by distance. This pattern is overlaid with signatures of recent gene flow, likely facilitated by late Pleistocene and ongoing anthropogenic landscape change. We demonstrate that the divergent effects of landscape history can overwhelm the homogenising effects of life-history traits that connect populations, even in a highly vagile species.

Turtles of the World: Annotated Checklist and Atlas of Taxonomy, Synonymy, Distribution, and Conservation Status (8th Ed.)

“…92. Chelodina (Chelodina) longicollis: Hodges et al (2015) studied mitochondrial phylogeography of Chelodina longicollis, a highly terrestrially mobile freshwater species, to determine if its population genetic structure would correspond to hydrological boundaries or not. They found two ancient haplogroups broadly with east-west partitioning across the Great Dividing Range, but made no taxonomic recommendations.…”

Lines in the land: a review of evidence for eastern Australia's major biogeographical barriers to closed forest taxa

“…A). The Cassilis Gap is geologically more ancient than the proposed Neogene–Quaternary contraction of closed forests and is thought to have facilitated movement of organisms from one side of the range to the other (Hobbs & Kaveney, ; Moore, ; Davies, ; Hodges, Donnellan & Georges, ). Nevertheless, the Cassilis Gap and the Hunter Valley lowlands may have acted in concert to impede longitudinal dispersal of closed forest taxa otherwise restricted to the mountaintops of the GDR and we consider them together here.…”

Where to draw the boundaries? Using landscape genomics to disentangle the scribbly gum species complex

“…Mountain ranges may not only act as barriers to species dispersal, but also serve as dispersal bridges (corridors) or reservoirs for biodiversity (Perrigo et al, 2020). For example, there are lower elevation areas in the Hunter River Valley across the GDR at the head of the Goulbourn River (i.e., the Cassilis Gap; Bryant and Krosch, 2016), which are thought to have facilitated historic movement of organisms from one side of the range to the other (Hobbs and Kaveney, 1962; Moore, 1970; Hodges et al, 2015). The importance of low‐elevation areas in mountain ranges as corridors for gene flow was supported by our analyses, which revealed that the Hunter River Valley was an area with high levels of introgression among scribbly gum taxa (Figure 6).…”