Morphological and genetic analysis of Galaxias ‘southern’ and G. gollumoides: interspecific differentiation and intraspecific structuring

Abstract

Morphometrics and amplified fragment length polymorphisms (AFLPs) were used to examine interspecific differentiation and intraspecific variation in two closely related freshwater fishes (Galaxias ’southern’ and G. gollumoides) using sympatric and allopatric populations. The two species were strongly differentiated across all populations, showing 19/24 distinctive morphological features and six fully diagnostic AFLPs. Morphological segregation was principally associated with G. ’southern’ having a larger upper jaw and smaller eye, suggesting that these characters may be useful for field discrimination. No hybridisation was observed between these two fishes, suggesting strong reproductive barriers and supporting species status. Both species showed intraspecific morphological variation among catchments, especially for traits associated with head and mouth morphology. Additionally, G. gollumoides showed intraspecific morphological variation among sites within two streams. Both species showed intraspecific genetic variation among catchments with the same four alleles differing among catchments for both species. Both species showed intraspecific genetic variation among sites within two streams, including consistent variation for the same two alleles. Intraspecific genetic structuring within streams suggests very limited movement among sections of streams. Consistent genetic and morphological variation in the same alleles and traits for both species suggests local adaptation and/or random genetic drift.