Temporal stability of a hybrid swarm between the migratory marine and estuarine fishes Acanthopagrus australis and A. butcheri
Roberts, D.G., Gray, C.A., West, R.J. and Ayre, D.J., 2011. Temporal stability of a hybrid swarm between the migratory marine and estuarine fishes Acanthopagrus australis and A. butcheri. Marine Ecology Progress Series, 421: 199 – 204.
Estuaries are potential hotspots of hybridisation between migratory marine and estuary-restricted species. Hybridisation rates may vary in space and time, reflecting the dynamic nature of estuaries and potentially widespread but erratic dispersal of marine taxa. Within estuaries, genotype frequencies may reflect past hybridisation events, with genetically intermediate and backcrossed individuals contributing to persistent hybrid swarms. On the south coast of NSW, hybridisation has occurred between estuarine black bream Acanthopagrus butcheri and marine yellowfin bream A. australis, but it is unclear whether this reflects a contemporary process. We recently found that, within lakes and lagoons at the southern range limit of yellowfin bream, hybrids were abundant and black bream extremely rare. Surprisingly, we detected hybrids within a small sample of fish from the Gippsland Lakes, an estuary 250 km further south. In the present study, we compare the genotypic composition of the contemporary Gippsland Lakes population of ‘bream’ with the historical composition revealed by analysis of museum specimens. The genetic makeup of samples varied little over time, with ancestral black bream virtually absent. Most individuals matched expectation for later-generation hybrids or black bream backcrosses, suggesting that the lakes have supported persistent hybrid swarms for many years. Our data imply that hybrid populations of ‘bream’ are more widespread and persistent than previously predicted.