Contrasting demographic histories in a pair of allopatric,sibling species of fish (Arripidae) from environments with contrasting glacial histories

Although Pleistocene glacial cycles are regularly used to explain many aspects of the demographic history of coastal marine species, the present study is one of few to test a priori predictions about these effects. Nucleotide sequence variation in the cytochrome b gene of the mtDNA and allele frequency variation at intron loci in the nDNA were compared between two species of Arripis (Australian Salmon) that are closely related and biologically similar other than for their allopatric distributions. The results suggest that A. truttaceus, which resides to the west of the Bass Strait, exhibits lower levels of genetic diversity and experienced a severe population bottleneck during the LGM followed by an expansion commencing some 17,000 years ago. In contrast, the population of A. trutta, which resides to the east of the Bass Strait, appears to have been largely unaffected by the LGM and has been expanding over the past 100,000 years or more. These results are consistent with a priori predictions, based on paleo-oceanographic data, that the demographic history of A. truttaceus has been more strongly affected by glacial periods by virtue of its distribution to the west of Bass Strait. Data on two other congeners are also presented to provide context for the results for A. trutta and A. truttaceus.