ALBERT

Notes: Abstract The genetic structure of the flounders Platichthys flesus L. and P. stellatus Pallas was investigated on different spatial scales through analysis of allozyme variation at 7 to 24 polymorphic loci in samples collected from different regions (Baltic Sea, North Sea, Brittany, Portugal, western Mediterranean, Adriatic Sea, Aegean Sea and Japan) in 1984 to 1987. No geographic variation was evident within a region. Some pattern of differentiation by distance was inferred within the Atlantic, while the Mediterranean comprised three geographically isolated populations and was itself geographically isolated from the Atlantic (fixed allele differences at up to three loci were found among P. flesus populations from the Atlantic, the western Mediterranean, the Adriatic Sea, the Aegean Sea and also P. stellatus from the coast of Japan). Sea temperature during the reproductive period probably acts as a barrier to gene flow between populations. Genetic distances among European flounder populations (P. flesus) were higher than, or of the same magnitude as, the genetic distance between Pacific (P. stellatus) and European flounder populations, suggesting that P. flesus is paraphyletic and/or there is no phylogenetic basis to recognising P. stellatus as a different species. The divergence between P. flesus and P. stellatus was thus inferred to be more recent than the divergence between the present P. flesus populations from the NE Atlantic and eastern Mediterranean. The eastern Mediterranean populations are thought to originate from the colonisation of the Mediterranean by a proto-P. flesus/P. stellatus ancestor, whereas the present western Mediterranean population has undergone a more recent colonisation event by P. flesus. Patterns of mitochondrial DNA variation, established on a smaller array of P. flesus samples, were in accordance with the geographic patterns inferred from the allozyme survey. In addition, they supported the hypothesis of a two-step colonisation of the western Mediterranean. These results contribute to our understanding of the biogeography of the Mediterranean marine fauna, especially the group of boreal remnants to which P. flesus belongs.

Notes: Variation of 14 enzyme systems encoded by 31 presumptive loci in different barbel species was studied using starch gel electrophoresis. Eighteen samples representing 11 Barbus tetraploid taxa were taken, including 10 populations from the Iberian Peninsula, six from other parts of western and southern Europe, one from northern Africa and one diploid species as outgroup from Asia Minor. The genetic analysis reassessed of the taxonomic status of the Iberian barbels into two distinct species groups. The first group included B. bocagei, B. comiza, B. graellsii, B. gulraonis, B. microcephalus, and B. sclateri, that aligned with B. callensis from northern Africa and with B. apoensis from Asia Minor; the other group included B. haasi and B. merldlonahs that was related to the European species, B. barbus, B. plebejus and B. peloponnesius. These groups are probably not monophyletic. It is suggested that the isolation of the Iberian Peninsula from Europe since the Oligocene-Miocene may explain the genetic affinities of the Iberian barbels with those of North African rather than with the European group.

Notes: Two species of coastal flatfish (brill and turbot, Scophthalmidae) were analysed electrophoretically at 17 common enzymatic loci in samples taken from 11 sites representing the species ranges in Europe. Brill showed a mean heterozygosity (H) of 0·11 while that of turbot was 0·02. The virtual absence of genetic diversity in turbot is probably due to a very low evolutionary rate, and provides little evidence for population substructure even if various signs indicate the possibility of a hidden differentiation (presence of the taxon maoetica in the Black Sea and differentiation of a species-specific cestode parasite on either side of the Strait of Gibraltar). On the other hand, the weak geographic structure in brill seems to result from rapid recolonization following the last ice age.

Notes: There were significant correlations between colour pattern, LDH-5*, genotype and certain meristic characters in 59 hybrid trout Salmo, sp. from the Volarja stream, Soca River basin, Slovenia. It is concluded that panmixia between native Salmo marmoratus, and introduced S. trutta, of Atlantic, Danubian and Mediterranean origin had not been reached in this zone, despite the long period of introgression. The result is in agreement with other studies dealing with introgression in Salmo, and for management purposes certain morphological characters, especially colour pattern, can be a valuable tool in restoring the marble trout population in the Soca River.

Notes: A capture-mark-recapture (CMR) study in a hybrid zone between two species of barbel, Barbus barbus and Barbus meridionalis, in the Lergue River (southern France) failed to reject the null hypothesis of no difference in survival among phenotypes. Power calculations indicated that very intensive fieldwork should be carried out if this hypothesis was to be investigated again. The study demonstrated, however, that there were marked differences in survival between upstream and downstream sites. It is suggested that there is an environmental gradient of selection along the hybrid zone (extrinsic component of natural selection).

Notes: The reproductive behaviour of two species of barbel (Barbus barbus and Barbus meridionalis) was investigated by means of aquarium experiments in several matings of six combinations. The reproductive behaviour of the two species appears to be similar and hybridizations were observed, showing that no complete behavioural barrier blocks the mating of the two species.

Notes: Analysis of trout from 13 stations on the Mediterranean slopes of the French Pyrenees by 31 presumptive enzyme loci demonstrated the major impact of restocking programmes. Although the annual introgression resulting from these introductions was small, the accumulation of genes of Atlantic origin has resulted in a change in allele frequencies. Genetic disequilibria within and between loci exist. Introgression by genes of domestic (hatchery) origin varied from 0 to 77% among stations. Natural Mediterranean populations show no detectable geographical structure. There was a direct relation between the degree of introgression and heterozygosity. However, restocking could not explain all of the observed genetic disequilibria.

Notes: Allozymes were used to analyse the genetic impact of hatchery brown trout Salmo trutt a, morpha fario stocked in wild Mediterranean populations to gain a better understanding of the mechanisms of introgression (regulation, elimination or homogenization). Analysis of the genetic structure of populations from the same river drainage basin but subjected to different incidences was performed in space and time (data on two generations and 2 years of sampling). Introgression is associated with high deficits of heterozygotes and linkage disequilibria. Genetic divergence according to age group was observed. These results may indicate selective forces acting against domesticated genes and limiting hybridization between the two forms.

Notes: Enzyme electrophoresis on horizontal starch gel was carried out on 356 barbel individuals. The sampling comprised 278 individuals of the species Barbus callensis from 10 rivers in Tunisia. The other individuals belonged to reference species (outgroups) from France and Morocco. An ecological study was also carried out on Tunisian rivers. The results show a clear differentiation of the two samples from northwestern Tunisia, which was only partly correlated with ecological characteristics of the rivers they inhabit. There is no genetic cline, but rather a discontinuity between populations in the northwestern-most watershed and all the other Tunisian populations. This differentiation probably has a paleohistoric origin not only related to adaptation to ecological conditions but also to difficulties in colonizing the watersheds. The results do not indicate clearly a colonization direction for the genus Barbus in North Africa. Analysis of the Algerian populations would appear to be indispensable. Lastly, in contrast with the usual taxonomy, Morocco and Tunisia are populated by two closely related species, but B. callensis should remain the name of the Tunisian species, which was the first to be described in the small El Kebir basin, a river that flows from Tunisia to Algeria.

Notes: The intergeneric hybridization of two Greek cyprinids reported by Crivelli & Dupont (1987) using morphological criteria is described here on the basis of 24 enzyme loci. This hybridization was rarely found to go beyond the first generation (backcrosses: 0–2 per 1000). Various statistical coefficients indicate that the hybrids correspond to an entity that is exactly halfway between the two parent species