Recent evolution of population structure in Australian barramundi, Lates calcarifer (Bloch): An example of isolation by distance in one dimension

Abstract

New and previously published genetic data from 6000 barramundi comprising 50 collections across tropical Australia were analysed for evidence of population subdivision. Sixteen discrete populations were identified, including four populations that were identified from new collections. Duplicate collections from two localities were statistically homogeneous after seven years between collections. Environmental and genetic factors that yielded the observed genetic pattern were investigated. Geological evidence of sea-level changes, when compared with bathymetry data for the region, reveals that barramundi must have recently recolonized many of the coastal estuaries of tropical Australia. This recolonization resulted from the inundation of the Gulf of Carpentaria and Torres Strait by a rapid rise in sea level of at least 130 m between 18 000 and 6000 years ago. The genetic data clearly indicate that, as the population spread into new habitats, there was a corresponding decrease in genetic diversity. This observed decrease has been maintained despite continued migration between populations. The 'onedimensional stepping stone' migration model, which most closely fits the observed population structure, predicts that the observed level of population subdivision (FST = 0.064) is maintained against substantial gene flow between adjacent populations. This contrasts with the predictions of the often-used 'island model' which gives estimates of Nem at least two orders of magnitude lower than those from the onedimensional stepping-stone model.

Concordance between dispersal and mitochondrial gene flow: isolation by distance in a tropical teleost, Lates calcarifer (Australian barramundi)

“…Some of our localities fall within a population boundary proposed by Keenan (1994). For example, Keenan's study could not discriminate between Mitchell, Flinders and Leichardt localities in the Gulf of Carpentaria despite large sample sizes (average n = 200) and high statistical power.…”

“…Random samples of 30 individuals are sufficient to detect at least one copy of all haplotypes that occur at 10 per cent frequency with 95 per cent confidence (Schwager et al, 1990). Temporal variation in haplotype frequencies was assumed not to vary significantly over the sampling period, an assumption with some empirical support from allozyme data (Keenan, 1994).…”

“…The most striking pattern is the large genetic differentiation among regions characterized by completely unique haplotypes. Keenan (1994) conducted an extensive analysis of L. calcarifer allozyme variation in 6000 individuals over 5500 km of coastline. Several features of Keenan's data are of particular relevance.…”

Mitochondrial genealogy of Western Australian barramundi: applications of inbreeding coefficients and coalescent analysis for separating temporal population processes

“…Genetic differences among barramundi populations have been described for the Australian fishery eastwards from the Ord River (Fig. 1) in Western Australia (Shaklee et al, 1993;Keenan, 1994). Keenan (1994) thought the generally low levels of heterozygosity found in Australian barramundi were due to founder effects of populations that have recolonized rapidly many tropical Australian estuaries during the most recent changes in sea levels.…”

“…1) in Western Australia (Shaklee et al, 1993;Keenan, 1994). Keenan (1994) thought the generally low levels of heterozygosity found in Australian barramundi were due to founder effects of populations that have recolonized rapidly many tropical Australian estuaries during the most recent changes in sea levels. According to this scenario, primary eastern and western source populations of barramundi were split by the Australia/New Guinea land bridge.…”