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The Australian Wet Tropics (AWT) is home to extremely high levels of species diversity and endemism. Within the AWT 75% of diversity comes from insects and other invertebrates, making them an excellent study system to analyze patterns of evolutionary phylogeography. Current knowledge about Zalmoxis (Arthropoda: Arachnida: Opiliones: Laniatores) diversity and distribution in Australia is limited, but can be address larger questions like how much diversity is there within the group, when and how did they first get to Australia, and what types of habitats support the leaf-litter dwelling creatures. Using recently collected and museum specimens, an updated multilocus molecular phylogeny was generated, supporting the description of one putative new species, Z. sp. n. “hypillian”, but also leaving unresolved relationships between previously described Z. cardwellensis and Z. furcifer. Geographic Information Systems (GIS) was used to model species distributions across the continent, showing Z. cardwellensis and Z. furcifer to have the largest known ranges. Intriguingly, Z. furcifer is found on both sides of the Black Mountain Corridor, an area of the AWT with unusually low levels of diversity that is thought to have been uninhabitable to most slow dispersing animals since the Pleistocene, serving as a physical barrier and cut-off to species ranges. This suggests that the BMC, and patterns of historical habitat suitability, might have played a less significant role limiting Zalmoxis distribution compared to other Wet Tropics species. Although Zalmoxis have been found in multiple Australian states, there was little support for or against a monophyletic Australian group sharing one common ancestor. However, Zalmoxis species known only from Queensland were found to be monophyletic, or each other's closest relatives. Based on BEAST Bayesian molecular clock analysis, the first Zalmoxis is estimated to have appeared in Australia during the late Cretaceous (89.5 - 76.5 Mya) with the Queensland clade originating in the Paleogene (54 - 70 Mya). These dates are too recent to be a result of ancient vicariance via land dispersal, since they occurred far after the breakup of supercontinent Gondwana. But they are also too ancient to consider dispersal during more recent glacial cycling when instances of land connections between Australia and neighboring islands are known. This suggests that Zalmoxis arrival in Australia was likely a result of trans-oceanic dispersal, one or more ancient lineages crossing the ocean from neighboring island populations. While impossible to prove, this theory has become an increasingly popular explanations of the ancient arrival of other endemic Australian species. Finally, MaxEnt species distribution modeling was used to identify coastal Queensland and northwestern Australia as areas most likely for Zalmoxis to occur. These habitats have dense vegetation, and are classified as rain fed pasture, forested areas, open tussock grass areas, or near inland water bodies. Zalmoxis occurrence was also correlated with high precipitation levels and low temperature variation. These are climatic conditions that facilitate vegetation growth, which is key to the survival of leaf-litter dwelling Arachnids. Overall the study left many unanswered questions due to small sample size, and further research into the Australia Zalmoxis system is necessary to identify and describe new species, resolve phylogenetic species relationships, allow for more robust age estimates, and provide insight into Australian evolutionary history.
Johnson, Joanne E., "Zalmoxis Diversity, Distribution, and Dispersal in Australian" (2016). Biology Honors Projects. 15.
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