ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.

Examining Hypotheses Of Historical Isolation And Contemporary Gene Flow Among Populations Of An Estuarine-Dwelling Sparid Spanning The Presently Inundated Bassian Land Bridge

C.P. Burridge¹, A.C. Hurt^{1, 3}, L.W. Farrington^{1, 4}, P.C. Coutin³, C.M. Austin¹

¹School of Ecology & Environment, Deakin University, PO Box 423 Warrnambool, VIC 3280, Australia
²Marine & Freshwater Resources Institute, PO Box 114, Queenscliff, VIC 3225, Australia.
³Present address: World Health Organisation Collaborating Centre for Reference and Research on Influenza, 45 Popular Road, VIC 3052, Australia.
⁴Present address: Applied Ecology Research Group, University of Canberra, Bruce, ACT 2601, Australia.
Email: chrisb@deakin.edu.au

Allozyme and mitochondrial DNA variation was surveyed in the black bream Acanthopagrus butcheri (Munroe), to examine the pattern of gene flow among estuaries in the vicinity of the presently inundated Bassian land bridge of southeastern Australia. Allozymes distinguished two peripheral samples from the remaining six, although the pattern of genetic variation could owe more to selection than reproductive isolation. Mitochondrial DNA distinguished the majority of samples from one another, and the pattern of variation was consistent with isolation by distance. Consequently, contemporary gene flow, mostly between adjacent estuaries, is evident across sample sites. However, there is some genetic signal consistent with the historical isolation of populations either side of the land bridge, followed by secondary intergradation. Reduced population subdivision observed from allozymes in southeastern Australia compared with Western Australia could be explained by differences in the recency of colonisation or a correlation between gene flow and river discharge. The levels of genetic divergence among A. butcheri relative to other estuarine fishes are consistent with differences in life histories. Implications of our data for fisheries management and aquaculture shall be discussed.

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