Extensive Genetic Connectivity and Historical Persistence Are Features of Two Widespread Tree Species in the Ancient Pilbara Region of Western Australia.

Heidi M Nistelberger,Stephen Van Leeuwen,Margaret Hankinson,Rachel M Binks,Margaret Byrne,David J Coates,Bronwyn M Macdonald,Shelley L Mcarthur

doi:10.3390/genes11080863

Heidi M Nistelberger, Stephen Van Leeuwen + Show 6 more

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https://doi.org/10.3390/genes11080863

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Abstract

Phylogeographic studies can be used as a tool to understand the evolutionary history of a landscape, including the major drivers of species distributions and diversity. Extensive research has been conducted on phylogeographic patterns of species found in northern hemisphere landscapes that were affected by glaciations, yet the body of literature for older, unaffected landscapes is still underrepresented. The Pilbara region of north-western Australia is an ancient and vast landscape that is topographically complex, consisting of plateaus, gorges, valleys, and ranges, and experiences extreme meteorological phenomena including seasonal cyclonic activity. These features are expected to influence patterns of genetic structuring throughout the landscape either by promoting or restricting the movement of pollen and seed. Whilst a growing body of literature exists for the fauna endemic to this region, less is known about the forces shaping the evolution of plant taxa. In this study we investigate the phylogeography of two iconic Pilbara tree species, the Hamersley Bloodwood (Corymbia hamersleyana) and Western Gidgee (Acacia pruinocarpa), by assessing patterns of variation and structure in several chloroplast DNA regions and nuclear microsatellite loci developed for each species. Gene flow was found to be extensive in both taxa and there was evidence of long-distance seed dispersal across the region (pollen to seed ratios of 6.67 and 2.96 for C. hamersleyana and A. pruinocarpa, respectively), which may result from flooding and strong wind gusts associated with extreme cyclonic activity. Both species possessed high levels of cpDNA genetic diversity in comparison to those from formerly glaciated landscapes (C. hamersleyana = 14 haplotypes, A. pruinocarpa = 37 haplotypes) and showed evidence of deep lineage diversification occurring from the late Miocene, a time of intensifying aridity in this landscape that appears to be a critical driver of evolution in Pilbara taxa. In contrast to another study, we did not find evidence for topographic features acting as refugia for the widely sampled C. hamersleyana.

Highlights

Studies of intraspecific phylogeography provide insight into the evolutionary history of a species, revealing forces that have shaped its distribution and diversity
Areas of topographic complexity and/or climatically buffered regions within older landscapes have been identified as putative refugia for many species during periods of climate fluctuation, yet these patterns are often idiosyncratic in nature, with locations of refugia varying amongst taxa [7,11,12,13,14]
There was no indication of null alleles in either data set with no significant difference between estimates of FST based on ENA corrected and uncorrected allele frequencies (Table S4)

Summary

Introduction

Studies of intraspecific phylogeography provide insight into the evolutionary history of a species, revealing forces that have shaped its distribution and diversity. Comparative phylogeography, for example, revealed the varied responses of species to glaciation during the last glacial maximum (LGM), including the consequences of expansion from major refugia [1] as well as persistence in localised idiosyncratic refugia within major refugial regions [2,3]. Parts of eastern North America, have identified high genetic diversity and structure in comparison to younger landscapes affected by glaciations [2,4,5,6,7,8] This has been attributed both to a lack of extinction due to relative climate stability and extensive localised persistence of populations allowing for the accrual of genetic variation [9,10]. Drawing broad conclusions from these older landscapes is hampered by the long history of species’ persistence as well as the individualised responses of species and populations to landscape features and climate phenomena [8]

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