Antarctic krill (Euphausia superba Dana) is a key species in the Antarctic food web and occurs on a circumcontinental scale. Population genetic structure of this species was investigated by sequence analysis of the ND1 mitochondrial gene in four population samples collected at di¡erent geographical localities around the Antarctic continent. Results indicate the existence of signi¢cant genetic di¡erences between samples, and we suggest that oceanographic barriers could be su¤ciently strong and temporally stable to restrict gene £ow between distinct areas. Moreover, our data indicate that Antarctic krill is not at mutation^drift equilibrium and that the species possibly has a low e¡ective population size as compared to the census size.

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We report the isolation and sequencing of 400-550 base pairs (bp) of the mitochondrial DNA (mtDNA) control region of eight species of Sparidae (Perciformes, Teleostei). This sequence information allowed us to design specific primers to one of these species (Pagellus bogaraveo). The new set of primers was used to test a rationalized approach to study the mtDNA nucleotide variability at the intraspecific level. The single-strand conformation polymorphism (SSCP) technique was applied to detect sequence variation in two non-overlapping fragments of the control region of 32 individuals of P. bogaraveo. To assess the sensitivity of the method, the nucleotide sequence of the analysed region was determined for all the specimens. The results showed that, for one of the two fragments, SSCP analysis was able to detect 100% of the underlying genetic variability. In sharp contrast, nucleotide variation of the second DNA fragment was completely unresolved by SSCP under different experimental conditions. This suggests that the resolution power of SSCP is crucially dependent on the nature of the fragment subjected to the analysis; therefore, a preliminary test of the sensitivity of the method should be performed on each specific DNA fragment before starting a large-scale survey. A rationalized approach, combining the SSCP technique and a simplified sequencing procedure, is proposed for studying intraspecific polymorphism at the mtDNA control region in fish.

Five loci amplified successfully and were polymorphic (Table 1). Two other loci also amplified products, but persistent stuttering prevented reliable scoring despite optimization and, in one case, primer redesign. Locus Co12E10 showed significant deviation from Hardy-Weinberg equilibrium ( χ 2 -test; P < 0.05). Null allele frequency estimates using cervus (Marshall et al . 1998) indicated possible null alleles at loci Co12E10 (frequency = 0.086) and Co9C11 (frequency = 0.031). At locus Co12E10 a consistently nonamplifying offspring further suggested the presence of a null allele (Pemberton et al . 1995). Caution is therefore required for parentage assignment based on exclusion at this locus. ReferencesCarpenter GC, Badham JA, Kimble B (1970) Behaviour patterns of three species of Amphibolorus (Agamidae). Copeia , 1970 , 497-505. Cogger HG (1978 Reproductive cycles, fat body cycles and sociosexual behaviour in the mallee dragon, Amphibolurus fordi (Lacertila: Agamidae).