Biological Journal of the Linnean Society (2001), 72: 333–343. With 6 figures doi: 10.1006/bijl.2000.0483, available online at http://www.idealibrary.com on
Evidence for long-distance dispersal in a sedentary passerine, Gymnorhina tibicen (Artamidae) ANDREW M. BAKER1∗, PETER B. MATHER1 and JANE M. HUGHES2 1
School of Natural Resource Sciences, Queensland University of Technology, Gardens Point Campus, GPO Box 2434, Brisbane, Queensland, 4001, Australia 2 Australian School of Environmental Studies, Griffith University, Nathan, Queensland, 4111, Australia Received 18 February 2000; accepted for publication 9 August 2000
Australian magpies (Gymnorhina tibicen) are group-living birds found across much of mainland Australia. Adults commonly remain in a breeding territory until death. Young of the year either remain on the natal (birth) site or are forced by their parents to disperse. Observational studies in south-eastern Australia suggest that most dispersing juveniles settle within 7 km of their natal territory. Therefore, despite potential for considerable gene flow (via flight), social organization predisposes magpies towards local population structuring. In this study, we measured genetic variation at both nuclear (allozyme) and mitochondrial loci and found evidence of substantial gene flow over very large distances (up to 1599 km). Thus, some juvenile magpies may disperse much greater distances than was previously thought. For mtDNA, geographic and genetic distance were strongly correlated, consistent with a pattern of isolation by distance. Therefore, although female gene flow is substantial it is apparently geographically restricted over large distances, in approximately a stepping-stone fashion. We conclude that a strong relationship between gene flow and geographic distance can develop even over large distances if populations have experienced 2001 The Linnean Society of London no major historical disturbances to gene flow. ADDITIONAL KEYWORDS: Australian magpie – bird – natal site – mitochondrial DNA – control-region – allozymes – gene flow – isolation by distance – geographic distance.
on a single genetic marker (Moritz, 1994); since markers can evolve at different rates they may indicate different rates of dispersal. When used together, observational and genetic data have the potential to provide more accurate information about a species’ dispersal behaviour than can either method in isolation (Moritz, 1994; Peacock, 1997). In spite of this, interpretation of such combined data sets is made difficult for many species because the observed patterns of dispersal are at odds with inferences about dispersal based on the genetic data. In birds, a commonly emerging scenario appears to be limited observed dispersal in parallel with genetic evidence of large-scale gene flow (e.g. Edwards, 1993; Kvist et al., 1998; da Silva & Granadeiro, 1999). Observational data suggests that gene flow is likely to be limited in the Australian magpie (Gymnorhina tibicen Latham 1802), however, the population genetic structure of this species is unknown. Previous studies of G. tibicen populations in south-eastern Australia suggest that juveniles will either remain on the natal site (Carrick, 1972; J. Hughes, unpublished data) or
INTRODUCTION Evolutionary biologists have been able to assess the geographic scale of dispersal from both a genetic and observational perspective for only a handful of avian species (see Stangel, Lennartz & Smith, 1992; Edwards, 1993; Bell, 1992 in Slatkin, 1993; Kidd & Friesen, 1998; da Silva & Granadeiro, 1999; McDonald et al., 1999). Such studies are rare, both because observational data on dispersal typically take years to compile and because it often proves difficult to retrieve sufficient genetic samples of the species under study to examine even superficially the relationship between gene flow and geographic proximity. Moreover, just as observational studies of dispersal have been criticised because they may not detect the settling location of all dispersers due to a limited study area (Koenig, Van Vuren & Hooge, 1996), genetic studies may be criticised for making inferences about dispersal behaviour based
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disperse very short distances (e.g.
