Genetic population structure of the mackerel icefish, Champsocephalus gunnari, in Antarctic waters

Genetic population structure of the mackerel icefish, Champsocephalus gunnari, in waters from around South Georgia, South Orkneys, and Heard Island (Australian Antarctic) was examined using allozyme electrophoresis.
Icefish were collected from Heard Island (N = 47; November 1990), South Georgia (N = 267; January/February 1991) and the South Orkneys (N = 44; January/February 1991) and subjected to starch gel electrophoresis. sixteen putative enzyme-coding loci were examined, of which 7 were polymorphic at the 0.95 criterion: glutamate oxaloacetate transaminase, GOT-I 2.6.1.1; α - glycerophosphate dehydrogenase, α-GPDH 1.1.1.8; isocitrate dehydrogenase, ICD 1.1.1.42; malate dehydrogenase, MDH-III 1.1.1.37; mannose phosphate isomerase, MPI 5.3.1.8; phosphoglucose mutase, PGM-II 2.7.5.1; superoxide dismutase, SOD 1.15.1.1).
Routine scoring of 358 fish at the 16 loci revealed below average levels of genetic variability, with the proportion of polymorphic loci, P = 0.175, mean heterozygosities per locus, HL = 0.058, and the effective number of alleles = 1.04 - 1.88.
The majority of alleles conformed to Hardy-Weinberg expectations, with significant deviations due exclusively to heterozygote deficiencies. Genetic differentiation was detected among samples, both within (South Georgia) r and between (South Georgia vs. Shag Rocks; South Georgia vs. South Orkneys) sea areas. Nei’s (1973) gene diversity analysis indicated that over 85% of the total gene diversity was due to the within-population component, with progressively higher between population values with increasing geographic separation. Samples from Heard Island were most genetically distinct ( I = 0.900 - 0.930; D = 0.072 - 0.106).
The apparent erosion of genetic variability may be related to abrupt changes in population size. Enhanced mobility of fish between sea areas was suggested by an overall reduction in genetic differentiation within and between South Georgia and Shag Rocks (compared with 1990), and the greater conformity to Hardy-Weinberg equilibrium. Genetic data support the notion of at least partial migration of C. gunnari between South Georgia and the South Orkneys, and possible speciation on a geographic scale.