Galaxias maculatus: An explanation of its biogeography

Abstract

Galaxias maculatus is a small diadromous fish found in Australia, New Zealand, South America and on some oceanic islands. Two hypotheses have been advanced to explain this widespread, disjunct distribution. McDowall promoted dispersal through the sea of salt-tolerant juveniles but Rosen and others claimed that the distribution reflected the break-up of Gondwana and subsequent drift of the southern continents. Allozyrne electrophoresis of muscle extracts of specimens of Galaxias maculatus from eastern and western Australia, New Zealand and Chile was used to test the hypothesis that populations of G. maculatus from the western Pacific and the eastern Pacific do not differ genetically. FST based on allele frequencies and genotypes was 0.14, suggesting only minor differentiation between eastern and western Pacific populations. Minor differentiation in allele frequency existed at some loci, but no fixation of alternative alleles has occurred. The populations examined appear to be part of the same gene pool, indicating that gene flow via dispersal through the sea occurs today. It is unlikely that South American and Australasian populations would be conspecific if they have exchanged no migrants since the break-up of Gondwana at the end of the Mesozoic.

Spatial and temporal distribution of landlockedGalaxias maculatusandGalaxias platei(Pisces: Galaxiidae) in a lake in the South American Andes

“…Although they are congeneric, they seem to represent two stocks long separated from each other (McDowall 1971). Galaxiids seem to belong to a pan-Austral Gondwanan biota that was fragmented in the Mesozoic (Croizat et al 1974;Rosen 1974Rosen , 1978, but results obtained by Berra et al (1996) support McDowall's (1970 dispersal hypothesis (movement through the sea). During the recent post-glacial period the lakes in the Andes were probably colonised by fish coming from two areas at the same time.…”

Life History Patterns and Biogeography: An Interpretation of Diadromy in Fishes1

“…The arguments for dispersal (e.g., Gross, 1987;McDowall, 1970McDowall, , 1988McDowall, , 2001McDowall, , 2002Berra et al, 1996;Keith, 2003), vicariance (e.g., Rosen, 1974;Croizat et al, 1974), or some combination of the two (e.g., Choudhury & Dick, 1998) as explanations for the distribution of diadromous taxa, especially the antitropical salmoniform fishes, have been debated extensively. Likewise, broad geographic ranges have been interpreted as explicit evidence of dispersal (e.g., McDowall, 2001McDowall, , 2002, of vicariance (e.g., Rosen, 1974), or of either dispersal or vicariance (Leis, 1984).…”

“…A decade before he defined diadromy, Myers (1938) proposed divisions of freshwater fish taxa based on their ability to tolerate saltwater: freshwater fishes, including primary division freshwater fishes (no salt tolerance), secondary division freshwater fishes (some salt tolerance), and peripheral or migratory fishes (diadromous) versus marine fishes (salt tolerant). These categories have been incorporated into fish biogeography and are still used broadly today (e.g., McDowall, 1988;Helfman et al, 1997;Berra, 2001). (The category of primary division freshwater fishes was modified by paleontologist Colin Patterson [1975], who recognized archaeolimnic taxa, those inferred to have originated and always lived in freshwaters, and telolimnic, those living in freshwater now, but not necessarily throughout their history.…”

Blood cytology of the common jollytail (Galaxias maculatus) (Jenyns, 1842) (Osmeriformes: Galaxiidae) at postlarval and adult stages

“…The wide geographical distribution of this species and its interesting ecological attributes, as well as the existence of diadromic behavior, have attracted the attention of many ichthyologists. There are numerous studies related to different aspects (systematic, biology, natural history, population genetics, etc) of G. maculatus (Campos 1970, McDowall 1970, McDowall 1971, McDowall 1981, McDowall 1984, McDowall 1988, Berra et al 1996, Waters and Burridge 1999, Busse and Möser 2006. However, there are still many unknown biological aspects.…”