title: Did postglacial sea-level changes initiate the evolutionary divergence of a Tasmanian endemic raptor from its mainland relative?
abstract: Populations on continental islands are often distinguishable from mainland conspecifics with respect to body size, appearance, behaviour or life history, and this is often congruent with genetic patterns. It is commonly assumed that such differences developed following the complete isolation of populations by sea-level rise following the Last Glacial Maximum (LGM). However, population divergence may predate the LGM, or marine dispersal and colonization of islands may have occurred more recently; in both cases, populations may have also diverged despite ongoing gene flow. Here, we test these alternative hypotheses for the divergence between wedge-tailed eagles from mainland Australia (Aquila audax audax) and the threatened Tasmanian subspecies (Aquila audax fleayi), based on variation at 20 microsatellite loci and mtDNA. Coalescent analyses indicate that population divergence appreciably postdates the severance of terrestrial habitat continuity and occurred without any subsequent gene flow. We infer a recent colonization of Tasmania by marine dispersal and cannot discount founder effects as the cause of differences in body size and life history. We call into question the general assumption of post-LGM marine transgression as the initiator of divergence of terrestrial lineages on continental islands and adjacent mainland, and highlight the range of alternative scenarios that should be considered.
authors.affiliation: School of Zoology, University of Tasmania, , Hobart, Tasmania 7001, Australia, Department of Primary Industry, Parks, Water and Environment, , Hobart, Tasmania 7001, Australia, Australian Centre for Ancient DNA, School of Earth and Environmental Sciences and Environment Institute, University of Adelaide, , North Terrace, Adelaide, South Australia 5005, Australia, School of Biological Sciences, Flinders University, , GPO Box 2100, Adelaide, South Australia 5001, Australia, Evolutionary Biology Unit, South Australian Museum, , North Terrace, Adelaide, South Australia 5001, Australia, Hydro Tasmania, , GPO Box 355, Hobart 7001, Australia, Sciences Department, Museum Victoria, , Carlton Gardens, Melbourne, Victoria 3001, Australia.
authors.forename: C P
authors.initials: CP
authors.lastname: Burridge
authors.forename: W E
authors.initials: WE
authors.lastname: Brown
authors.forename: J
authors.initials: J
authors.lastname: Wadley
authors.forename: D L
authors.initials: DL
authors.lastname: Nankervis
authors.forename: L
authors.initials: L
authors.lastname: Olivier
authors.forename: M G
authors.initials: MG
authors.lastname: Gardner
authors.forename: C
authors.initials: C
authors.lastname: Hull
authors.forename: R
authors.initials: R
authors.lastname: Barbour
authors.forename: J J
authors.initials: JJ
authors.lastname: Austin
mesh_terms: D063147:Animal Distribution; D000818:Animals; D001315:Australia; D049628:Body Size; D004272:DNA, Mitochondrial / Q000737:chemistry; D020307:Eagles / Q000033:anatomy & histology / Q000235:genetics*; D051456:Gene Flow; D049810:Genetic Speciation; D014644:Genetic Variation; D018895:Microsatellite Repeats; D009792:Oceans and Seas; D011157:Population Dynamics; D060047:Reproductive Isolation; D013648:Tasmania
chemical_list: D004272:DNA, Mitochondrial
keywords: Last Glacial Maximum; inbreeding depression; marine dispersal; sea level; subspecies; vicariance