Electrophoretic data were analysed from 49 species of freshwater fish, 57 species of marine fish, and seven anadromous species. For each species, at least 15 individuals had been assayed for at least 15 loci in two or more subpopulations. The results showed that while average total heterozygosity (H̄T) was approximately equal in freshwater and marine species (0·062 and 0·064 respectively), subpopulation heterozygosity (H̄s) was significantly less in the former group (0·046 and 0·059 respectively). Consequently the average degree of genetic subpopulation differentiation (H̄ST) was significantly greater for freshwater species (0·222 v. 0·062). On average, it is likely that marine subpopulations exchange between 10 and 100 times more migrants per generation than freshwater subpopulations, presumably because of the relative absence of barriers to dispersal in the marine environment. The reduced values of Hs in freshwater species are likely to reflect reduced effective subpopulation sizes relative to marine species. The few andromous species that have been analysed show intermediate levels of GST.

Random Amplified Polymorphic DNA (RAPD) analysis was applied to three species of the tilapia genus Oreochromis and four subspecies of 0. niloticus. Thirteen random lO-mer primers were used to assay polymorphisms within and between populations. Different RAPD fragment patterns were observed for different species, although not always for different subspecies. Evidence is presented that RAPD markers might be useful for systematic investigation at the level of species and subspecies.

StLircIi gel electrophoi-esis was used to study \-ariation at I I loci in mussels sampled mainly from British co'istal sites. Two types of mussel were identified, 2\f>sti"u ediilis, tlie common mussel rind its soutliern relatit e .\fvti/iir ga//n/~~,/,,or~iricin/i~. Se\ era1 partially dingnortic loci were used to miip tlie distrihtition of tlie t\vo forms. .\fvti/riJ ediilis \\as present ;it all sites sampled in Britain and Ireland hut \\as at low frequency in S\V England; .\I. ga//ul,ioi'incia/ir \vas detected in S\V England, tlie south and west of Ireland. Scotland and S E England. hut was absent from soutli \Vales. the Irish sea co;ists of tValt-s and Ireland. and SE England. Ap;irt fi-om tlie occurrence of . i f . gn//upinz,inrin/is in NE England. this distribution conforms bvith tlie results of studies using morphological characters and parallels the distrihution of many other soutlicrn species in Britain. At thc microgeographical l e d , .If. c d i i / i~ was foriitd to prcfrr more slieltered a n d rstiiarine conditions than :\I. ,~a//opmr,iiiria/i~. .Analysis rising the hest diagnostic loci sliowed that tiybridizati(in is occurring between .if, rdiilis and .\I. gn/lopiur~in~-ia/ir at all localities where the) occiir sympatrically hut that tlie extent of hybridization \aries considerahl) hetween localities. 'The distribution of localities ha\ ing Iiigli proportions of hybrid individuals is hest interpreted hy assuming that 11) hrids ha\ e higher fitness than parental tyries at these localities. :\ stlid! \v.is made o f \ ariation within and between those localities where only .\f. ~diilir indi\ idualsTvei-e ohser\.ed. Little significant geographic \.ariation in dlele frequency was detected, hut significcrnt deficits of 1ieteroz)gotes compared with H;irdy-lVeinberg expectations n e r e seen for most loci. .\n:ilysis suggests that the \Valilund effect is not involxd and that the most likely cause of tlie deficit is low frequencies (if niill 'illeles. In .\I. tdii/iJ no differences in phenotypic \.ariance in shell height and width v w e ohserved hetween samples of multiply lietcrozygoiis and multiply liomozygoiis individuals ;ind no qriietic differences were found bet\vern juveniles and adults. Overall little evidence was found t h a t Iialnncing selectinn is responsible for m'rintrn;ince of the polymoi-phisms studied in .if. edulir. 1 lie ~iatterii ofgcogr;ipliic \.ariation in gene frequencies in d i f v t i /~i s in the British Isles is discussed in relation to variation in tlie south and north of F.rirope and S o r t h . h e r i c a . It is concluded that steep clines in gene li-eqiiencies in .\I. idrrlis ohser\-ed h! otlier \viirkers in tlie Bnltir and in Long 1sl;ind Sound cannot tie .ittribiited to the presencr of .\I. gn//ol"ui,incin/i.

No abstract

Pooling of samples in proteomics experiments might help overcome resource constraints when many individuals are analysed. The measured biological variation should be reduced giving increased power to detect treatment differences. Pooling has been advocated in microarray work but there are few tests of its potential in proteomics. In this study, we examine three issues on which the success of the pooling approach might hinge and provide evidence that: (i) the protein expression in a pool matches the mean expression of the individuals making up the pool for the majority of proteins, although for some proteins the pool expression is different; (ii) the biological variance between pools is reduced compared with that between individuals, as predicted in theory, but this reduction is not as large as expected. A practical consequence of this is that power could be reduced; (iii) proteins detectable in individual samples are usually but not always visible when samples are pooled. We conclude that pooling of samples in proteomics work is a valid and potentially valuable procedure but consideration should be given to these issues in experimental design.

No abstract

Samples from the high and low shore were taken from mussel populations at two localities. Croyde Bay and Whitsand Bay in southwest England, within the zone of hybridisation of Mytilus edulis and Mytilus galloprovincialis, and analysed at five polymorphic allozyme loci.Strong correlations were observed between shell length and allele frequencies at both localities, with a higher frequency of alleles characterising M. galloprovincialis being found in larger mussels. Three hypotheses were considered as explanation of these results (1) differential mortality, (2) differential growth and (3) historical change within the hybrid zone. The last hypothesis was rejected because the pattern of length dependent allozyme variation was similar in samples taken in 1980-Si and 1986-87. The observation of small growth differences between M. edulis and M. galloprovincialis provided evidence against the second hypothesis. Thus, higher mortality of younger M. edulis was favoured as the cause of the length-dependent variation. Wave exposure and sand abrasion experienced by the mussels were thought to be the most likely selective factors.Strong correlations were also observed in these populations between shell length and allozyme heterozygosity. Analysis of genotype frequencies in small and large size classes of mussels provide evidence of a small added effect of heterozygosity, but no evidence of overdominance.

Many bivalve species, including mussels of the genus Mytilus, are unusual in having two mtDNA genomes, one inherited maternally (the F genome) and the other inherited paternally (the M genome). The sequence differences between the genomes are usually great, indicating ancient divergence predating speciation events. However, in Mytilus trossulus from the Baltic, both genomes are similar to the F genome from the closely related M. edulis. This study analyzed the mtDNA control region structure in male and female Baltic M. trossulus mussels. We show that a great diversity of structural rearrangements is present in both sexes. Sperm samples are dominated by recombinant haplotypes with M. edulis M-like control region segments, some having large duplications. By contrast, the rearranged haplotypes that dominate in eggs lack segments from this M genome. The rearrangements can be explained by a combination of tandem duplication, deletion, and intermolecular recombination. An evolutionary pathway leading to the recombinant haplotypes is suggested. The data are also considered in relation to the hypothesis that the M. edulis M-like control region sequence is necessary to confer the paternal role on genomes that are otherwise F-like. S TRICTLY uniparental inheritance of organelle genomes is a rule in nearly all anisogamic organisms. One of the most prominent exceptions is the mitochondrial inheritance system of mussels of the family Mytilidae in which separate maternal (the F genome) and paternal (the M genome) routes of mtDNA inheritance occur (for review, see Skibinski et al.1994a,b; Zouros et al. 1994a,b;Zouros 2000). This system, called doubly uniparental inheritance (DUI) (Zouros et al. 1994a), has also been observed in freshwater mussels of the family Unionidae (Hoeh et al. 1996;Liu et al. 1996) and clams of the family Veneridae (Passamonti and Scali 2001). Phylogenetic analysis indicates that divergence of the F and M genomes can be great, predating speciation events, and that role reversal or masculinization events, whereby the F genome takes on the role of the previous M genome, has occurred repeatedly in the evolution of marine mussels (Hoeh et al. 1996(Hoeh et al. , 1997, but is absent or less frequent in freshwater mussels (Hoeh et al. 2002).A hybrid zone separates Baltic Mytilus trossulus from North Sea M. edulis populations (see Riginos and Cunningham 2005 for review). Although there is little introgression of mtDNA between American M. trossulus and M. edulis (Saavedra et al. 1996;Comesana et al. 1999) in Baltic M. trossulus, the mtDNA in heteroplasmic male individuals is similar to that in the F genome from M. edulis (Quesada et al. 1995(Quesada et al. , 2003Wenne and Skibinski 1995; Zbawicka et al. 2003a,b). It appears that there has been complete asymmetric introgression of M. edulis F mtDNA into Baltic M. trossulus, accompanied by role reversal and masculinization (Rawson and Hilbish 1998;Quesada et al. 1999). These processes might be coupled and associated with cytonuclear incompatibilities that ...