Distinguishing past from present gene flow along and across a river: the case of the carnivorous marsupial (Antechinus flavipes) on southern Australian floodplains

Abstract

Humans have altered many floodplain ecosystems around the world by clearing vegetation, building towns and regulating river flows. Studies discerning gene flow and population structure of floodplain-dwelling animals are rare yet are necessary for understanding the effects of human actions on native populations. In southeastern Australia, the yellow-footed antechinus (Antechinus flavipes) is the only carnivorous marsupial on many lowland floodplains, yet our knowledge of impacts of human activities is limited. The control region of mitochondrial DNA and 11 microsatellite DNA markers were used to explore historic and current gene flow in A. flavipes across and along the Murray River. Simulations were carried out to test different migration models. We found evidence for historic gene flow along and across the river but inferred that small towns and farmland or cleared floodplain sections restricted current gene flow along the river. Populations along the river appear to be isolated, and should be maintained at large enough sizes to avoid genetic problems such as inbreeding depression and loss of evolutionary potential. We also investigated whether 50-yearlong maintenance of high water levels for irrigation in summer, at the time of juvenile dispersal, has led to restrictions in gene flow across the river. We found no evidence for restrictions to gene flow across the river and suggest that large floods and dropping tree branches may aid dispersal across the river.

Restricted gene flow in the endangered pygmy bluetongue lizard (Tiliqua adelaidensis) in a fragmented agricultural landscape

“…Movement of individuals among isolated populations of T. adelaidensis should thus be restricted to sites that were connected before agricultural development and have similar local environmental conditions. Continued work to distinguish between historic and contemporary gene flow could help identify previously connected populations (Hansen and Taylor 2008;Lada et al 2008). Furthermore, combining the present genetic study with further studies of ecological similarity or divergence would help determine which local populations are exchangeable (Rader et al 2005).…”

“…However, results from our spatial autocorrelation analysis revealed a significant genetic structure within habitat patches at a fine scale (<400 m); thus, genetic structure over several kilometres would be expected with or without fragmentation. Lada et al (2008) combined genetic analysis with simulation modelling to distinguish between the current and historic gene flow among populations of a small, carnivorous marsupial. Such an approach could be useful in future studies of T. adelaidensis, provided that reliable estimates of population sizes can be obtained (Lada et al 2008).…”

“…Lada et al (2008) combined genetic analysis with simulation modelling to distinguish between the current and historic gene flow among populations of a small, carnivorous marsupial. Such an approach could be useful in future studies of T. adelaidensis, provided that reliable estimates of population sizes can be obtained (Lada et al 2008). …”

Towards modelling persistence of woodland birds: the role of genetics

“…A more sophisticated population genetic modelling approach can be used to compare different migration scenarios quantitatively (e.g. Lada et al 2008). Diverse software is available, including EASYPOP, MS, METas.IM, Geneland, IBDSIM, DIYABC and SPLATCHE (Balloux 2001;Currat et al 2004;Balkenhol et al 2009b;Guillot et al 2009).…”

Inference of Population History by Coupling Exploratory and Model-Driven Phylogeographic Analyses

“…For example, when N e is large, it can take a considerable amount of time for allele frequencies to diverge by genetic drift—even in the absence of gene flow [68]. Because population allele frequencies can be obtained directly from individual genotypes, the comparatively deeper temporal perspective from allele frequencies rather than individual-based genotypes can be extracted simply by employing the appropriate analyses.…”