Cladogenesis and Loss of the Marine Life-History Phase in Freshwater Galaxiid Fishes (Osmeriformes: Galaxiidae)

Abstract

Abstract. Switches from migratory (diadromous) to nonmigratory (freshwater) life histories are known to have occurred repeatedly in some aquatic taxa. However, the significance of the loss of diadromy as an initiator for speciation remains poorly understood. The rivers of New Zealand's South Island house a species flock of recently derived nonmigratory galaxiid fishes known as the Galaxias vulgaris complex. Members of this complex are morphologically and genetically similar to the diadromous G. brevipinnis found in New Zealand and southeastern Australia. We hypothesised that South Island's G. vulgaris complex (at least 10 nonmigratory lineages) represents a number of independent radiations from a migratory G. brevipinnis stock, with repeated loss of diadromy. Sequence data were obtained for 31 ingroup samples (G. vulgaris complex and G. brevipinnis) plus four outgroup taxa. A well-resolved phylogeny based on 5039 base pairs of the mitochondrial genome suggests that diadromy has been lost on three separate occasions. Thus, speciation in these galaxiid fishes is partly an incidental phenomenon caused by switches from diadromous to nonmigratory strategies. However, much of the subsequent nonmigratory diversity is monophyletic, suggesting that drainage evolution (vicariance) has also played a major role in cladogenesis. Levels of sequence divergence among major ingroup lineages (1.6-12.7%) suggest that the radiation is considerably older relative to Northern Hemisphere (postglacial) complexes of salmonid, osmerid, and gasterosteid fishes. Sympatric taxa are not monophyletic, suggesting that their coexistence reflects secondary contact rather than sympatric speciation. The monophyly of New Zealand G. brevipinnis is well supported, but both mitochondrial DNA and nuclear sequences indicate that G. brevipinnis is paraphyletic on an intercontinental scale. The divergence (maximum 11.5%) between Tasmanian and New Zealand G. brevipinnis, although large, supports marine dispersal rather than vicariance as the principle biogeographic mechanism on an intercontinental scale.

Life-history characteristics of eleotrid fishes of the western hemisphere, and perils of life in a vanishing environment

“…Some of these have undergone a secondary loss of diadromy. The stem diadromous species in this radiation was found to be G. brevipinnis (Waters and Wallis 2001). Other studies of amphidromous species showing non-migratory (freshwater) as well as diadromous populations include the eleotrid Gobiomorphus cotidianus (Closs et al 2003;Michel et al 2008).…”

“…Some diadromous fishes appear to follow more than a single life-history pattern among populations (facultative rather than obligate diadromy), (e.g., McDowall 1972;Waters and Wallis 2001;McDowall 2001McDowall , 2002Closs et al 2003;Iguchi 2007;Michel et al 2008). There are several studies illustrating that Gobiomorus dormitor shows such flexibility.…”

Microsatellite markers and mtDNA data indicate two distinct groups in dwarf galaxias, Galaxiella pusilla (Mack) (Pisces: Galaxiidae), a threatened freshwater fish from south-eastern Australia

“…that has since lost a marine life history and subsequently isolated populations into various freshwater systems. The loss of diadromy in New Zealand Galaxiidae fish has been reported by Waters and Wallis (2001).…”

The role of dams in altering freshwater fish communities in New Zealand

“…We expect that this is mainly due to the depauperate and unusual nature of the New Zealand fish fauna. For example, distinctive headwater communities can occur above dams in large catchments because historically their biogeographic isolation has resulted in speciation amongst non-migratory fish populations (Waters & Wallis 2001). Moreover, fish assemblages below dams are probably less variable because they are often composed of a similar pool of widely distributed diadromous species creating more homogeneous communities.…”