Pleistocene refugia in an arid landscape: analysis of a widely distributed Australian passerine

Abstract

While many studies have documented the effect that glacial cycles have had on northern hemisphere species, few have attempted to study the associated effect of aridification at low latitudes in the southern hemisphere. We investigated the past effects that cyclic aridification may have had on the population structure and history of a widespread endemic Australian bird species, the Australian magpie (Gymnorhina tibicen). One thousand one hundred and sixty-six samples from across its native range were analysed for mitochondrial control region sequence variation and variation at six microsatellite loci. Analysis of mitochondrial control region sequence data indicated monophyletic clades that were geographically congruent with an eastern and western region. The contemporary distribution of east and west clades is nonoverlapping but in close proximity. Populations were estimated to have diverged in the Pleistocene around 36,000 years ago. The putative Carpentarian and Nullarbor arid barriers appear to be associated with the divergence between east and west mainland populations. Nested clade analysis indicated a signature of range expansion in the eastern region suggesting movement possibly inland and northward subsequent to the last period of aridity. The island population of Tasmania was of very recent origin, possibly since sea levels rose 16,000 years ago. Given the east-west structure, there was no congruence between morphology and recent history of this species indicating a lack of support for morphological taxa. Overall mitochondrial DNA and microsatellite variation suggest that increasing aridity and Pleistocene refugia played a role in structuring populations of the Australian magpie; however, the dispersal ability and generalist habitat requirements may have facilitated the movement of magpies into an almost contiguous modern distribution across the continent. This study supports the idea that Pleistocene aridification played an important role in structuring intraspecific variation in low latitudinal southern hemisphere avian species.

Are lice good proxies for host history? A comparative analysis of the Australian magpie, Gymnorhina tibicen, and two species of feather louse

“…One common haplotype (bs1) within the northern clade (clade 2) was found in all northern populations distributed from the Kimberley (Km) region across to Rockhampton (Rk) in eastern Australia over a distance greater than 3000 km. Although maternal gene flow is absent in the host between northeast and northwest Australia, microsatellite data suggested that male magpie dispersal is occurring between northeast and northwest Australia (Toon et al, 2007). It is possible that B. semiannulata disperse primarily on male magpies Are lice good proxies for host history?…”

“…Philopterus sp. collected from Cape Crawford (Cc) belonged to a mtDNA clade restricted to northwestern populations, whereas magpies from the same site belonged to the eastern mtDNA magpie clade (Toon et al, 2007). Although no secondary contact was suggested between host mtDNA clades, gene flow was inferred from microsatellite data between northeastern and northwestern populations thereby potentially facilitating dispersal of western lice to eastern magpie hosts.…”

“…It is postulated that during glacial/arid periods in the Pleistocene, Australia was divided by arid barriers into at least six coastal refuges and an inland refuge in central Australia (Keast, 1961). From mtDNA analysis and estimates of population divergence, it is suggested that magpies were divided into at least two populations by the time of the most recent glacial/arid period (100 000-16 000 BP) that were most likely distributed along the east coast and the south west of the continent (Toon et al, 2007). It is possible that magpies also inhabited a third refuge in central Australia during the last glacial/arid period for a short period of time that was sufficient to allow divergence in the parasite and not in the host.…”

“…For the host, control region sequence variation was previously described in Baker et al (2000) and Toon et al (2007). Although use of an identical gene fragment for lice would have been preferred, the non-coding region of the mtDNA in lice is AT rich and greatly reduced in length (Covacin et al, 2006).…”

“…Three main plumage forms based on dorsal colour are currently recognized in Australia: black backed (BB) in northern Australia, white backed (WB) in southeastern Australia and Tasmania and white back males/black back females (varied) in southwestern Australia (Schodde and Mason, 1999). Phylogeographic analysis of magpie populations based on mitochondrial control region variation indicated shallow east-west structuring (Toon et al, 2007). It was estimated that populations had been isolated on either side of the continent in the late Pleistocene (less than 50 000 years).…”