POPULATION-GENETICS OF A CYCLOSTOME SPECIES PAIR, RIVER LAMPREY (LAMPETRA-FLUVIATILIS L) AND BROOK LAMPREY (LAMPETRA-PLANERI BLOCH)

Horizontal agarose gel electrophoresis of 24 allozyme loci in four spe cies of Central European lampreys (321 Lampetra planeri, 83 L. fluviat ilis, 11 Eudontomyzon mariae and nine Petromyzon marinus) was used to study the 'paired species' L. fluviatilis and L. planeri. The genetic differentiation of the anadromous river lamprey (L. fluviatilis) from the stationary brook lamprey (L. planeri) was within the range of ingr oup differentiation of the latter, but L. fluviatilis exhibited much g reater population cohesion over a more extended geographic range: G(ST ) = 0.0537 versus G(ST) = 0.3398, N(c)m = 4.402 versus N(c)m = 0.4856, mean genetic among-stock distances D = 0.0047 versus D = 0.0257. L. p laneri populations coexisting geographically with L. fluviatilis in th e Rhine and Elbe river systems were genetically more cohesive than L. planeri stocks from the Danubian basin where L. fluviatilis is absent. Danubian L. planeri populations exhibit a lower degree of heterozygos ity than brook lampreys from the Rhine river system, but comprise deep er genetic lineages (G(ST) = 0.4629 versus G(ST) = 0.2434), despite be ing sampled from a much more restricted area. Isolation-by-distance is observed for L. planeri from the Danubian but not from the Atlantic d rainage basins. Transspecific gene flow between L. planeri from Atlant ic drainage basins and the long-distant migrating L. fluviatilis is in ferred, raising doubt on the validity of two separate biospecies. E. m ariae and P. marinus are clearly differentiated from Lampetra spp. at several allozyme loci.