Enzyme variability at 28 presumptive gene loci was studied, by standard starch gel electrophoresis, in 30 populations belonging to the five recognized species of the landsnail Solatopupa from its entire NW Mediterranean range. Six genetically differentiated groups can be identified among the 30 populations sampled. These are distinguished by two to 19 diagnostic loci, different levels of genetic variability and populations genetics. They are also significantly different as far as the D values are considered. There is no evidence of gene flow among them. Genetically inferred groups correspond in four cases to morphologically distinguished species. In contrast, S. similis, as identified by morphological features, is likely to be a complex of at least two cryptic species. Populations and species of Solatopupa are characterized by: high fixation of alternative alleles both within and between species; medium‐lo‐low levels of genie variation; heterozygote deficiency; sharp genetic differentiation among population within species; restricted gene flow; and high genetic distances. Genetic variability is partly associated with climatic factors related to moisture. Both deterministic and stochastic processes may play a part in the genetic differentiation of Solatopupa snails. Founder events seem to be the main factor affecting the genetic structure of populations and perhaps also speciation. Solatopupa populations display many attributes of populations that may be expected to undergo speciation events involving reorganization of the whole genome after a founder event.

Abstract. Hymenoptera are haplodiploid and usually display very low genetic variation. Most data concern social or parasitic Apocrita, while the little information available for the primitive phytophagous species of the suborder Symphyta is contradictory. The present study is related to seven species of the genus Cephalcia, living in coniferous forests of Northern Eurasia and sharing spruce (Picea sp. pl.) as host plant. Individuals from 22 populations belonging to Cephalcia abietis, C. alashanica, C. arvensis, C. erythrogaster, C. fallenii, C. fulva, C. klugii from Europe and China were surveyed for genetic variation at 28 loci using enzyme electrophoresis. Pairs of sibling species were recognized within C. arvensis and C. fallenii, corresponding to different phenological and morphological forms. In the latter case, reproductive isolation in sympatry occurs despite low genetic distance (D --0.059). Large genetic distances and fixed alternate alleles were observed between Chinese and European populations of C. abietis and C. arvensis. Expected heterozygosity of Cephalcia populations (0.197, SD 0.064) is significantly higher than that of other Symphyta (Tenthredinoidea) (average H~xp 0.059, SD 0.032) (two-tailed Mann-Whitney test, Z = 4.39, p <0.01). These data suggest that haplodiploidy per se does not reduce the genetic variation in most Cephalcia populations. Most of the factors that can lower the potential for genetic diversity in a haplodiploid genetic system are not so effective in Cephaleia populations, which seem to be comparable to diplodiploid insect populations in diversity. In a few isolated populations the large number of fixed loci and the large genetic distances may support the predicted faster rate of fixation, as a consequence of haplodiploidy.

In the six species of Solatopupa, genetic information apparently disagrees with the taxonomic relationships already inferred from classical comparative analysis of shell morphology; a global reexamination of data in a phylogenetic perspective is therefore required. Different criteria of phylogenetic inference were applied to allozyme data from previous studies (28 loci) and to a matrix of 17 binary factors descriptive of morphological characters (shell and genital anatomy) with the purpose of making a comparative evaluation of the resulting branching patterns. Results show that, in spite of the initial suggestion, there is no inconsistency between genetically and morphologically inferred phylogenies, if the morphological data are thoroughly examined and globally considerd. These data, in fact, are more insidious to interpret and often misleading. In the case under study, the apparent similarity in the shell shape is probably ascribable to homoplasy, and likely to be the result of very different evolutionary processes all leading to a juvenilized (pedomorphic) shell morphology.

The meiotic and mitotic chromosomes of the five recognized species of Solatopupa Pilsbry 1917 are described and compared. Meiosis is of a standard type. The karyotype of S. psarolena (Bourguignat) with 2n=56 chromosomes and a conspicuously large metacentric pair is compared with those of S.pallida (Rossmässler) and S.simonettae (Giusti) having 2n=58 chromosomes, and with that of S.similis (Bruguière) which has 2n=60. A Robertsonian fusion could be linked with the splitting of S.psarolena from a common ancestor with the congeneric species. The diploid value 2n=58 is most probably the ancestral one.

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