6-Phosphogluconate dehydrogenase (PGD) allele phylogeny is incongruent with a recent origin of polyploidization in some North American Sphaeriidae (Mollusca, Bivalvia)

Comments on species divergence in the genus Sphaerium (Bivalvia) and phylogenetic affinities of Sphaerium nucleus and S. corneum var. mamillanum based on karyotypes and sequences of 16S and ITS1 rDNA

Chromosome, 16S and ITS1 rDNA sequence analyses were used to obtain reliable diagnostic characters and to clarify phylogenetic relationships of sphaeriid bivalves of the genus Sphaerium. The species studied were found to be diploid, with modal number 2n = 28 in S. nucleus and 2n = 30 in S. corneum var. mamillanum. Small, biarmed, C- negative B chromosomes were found in all studied populations of both species. Karyological and molecular markers revealed no differences between S. corneum s. str. and S. corneum var. mamillanum. No intraspecific differences were found in the basic karyotype of S. nucleus. Molecular analyses, however, uncovered three genetically distinct ITS1 lineages: one comprised of samples from Lithuania, Slovakia, and Russia, another from Czech, and a third from Ukraine. Additionally to known 16S haplotype from Ukraine, three new 16S haplotypes of S. nucleus were detected: one in the samples from Lithuania and Russia, one in Slovakian and one in Czech population. In the ITS1 phylogenetic tree, all branches of S. nucleus clustered in one clade. In the 16S phylogenetic tree, however, the haplotype of Czech S. nucleus formed a separate branch, distant from three other haplotypes of S. nucleus. Molecular results indicate that in the context of the Evolutionary Species Concept the S. nucleus morphospecies may represent a complex of separate taxa, however referring on the Biological Species Concept the genetic lineages could represent the intraspecific variability.

Androgenesis: a review through the study of the selfish shellfish Corbicula spp

Among the asexual reproductive modes, androgenesis is probably one of the most astonishing and least studied mechanisms. In this 'paternal monopolization', the maternal nuclear genome fails to participate in zygote development and offspring are paternal nuclear clones. Obligate androgenesis is known in only a few organisms, including multiple species of clam in the genus Corbicula. Corbicula is a good system to review the evolutionary consequences of this 'all-male asexuality' because the cytological mechanisms of androgenetic reproduction have been described. In Corbicula, sperm are unreduced and, after fertilization, the maternal nuclear chromosomes are extruded as two polar bodies. Hermaphroditic lineages of Corbicula have a worldwide distribution and seem to reproduce through androgenesis, whereas their sexual relatives have restricted ranges. The invasive success of these androgenetic Corbicula lineages may be linked to their asexual mode of reproduction. We review the phenomenon of androgenesis, focusing on evolutionary perspectives, using the genus Corbicula as an exemplar system.

E Pluribus Unum: A phylogenetic and phylogeographic reassessment of Laevapex (Pulmonata: Ancylidae), a North American genus of freshwater limpets

The North American freshwater limpet genus Laevapex (Walker, 1903) is a ubiquitous inhabitant of lentic and slow-moving lotic habitats east of the Rocky Mountains, but uncertainty clouds its systematic affinities, the phylogenetic validity of its constituent nominal species, and its degree of genetic connectivity among drainages. We addressed these issues by sampling the genus throughout much of its collective range and constructing representative nuclear and mitochondrial (mt) gene trees, in addition to performing morphometric analyses of shell shape variation. Our results identify neotropical Gundlachia and South American Uncancylus as sister lineages for Laevapex and reveal a pronounced sub-familial dichotomy within the Ancylidae, separating these three New World genera from a Holarctic (Ferrissia (Ancylus, Rhodacmea)) sister clade. Five nominal taxa (L. fuscus, L. diaphanus, L. peninsulae, L. sp., and "F."arkansasensis), indistinguishable in our morphometric analyses, were polyphyletic in the mt gene trees, exhibited modest levels (< 3.9%) of genetic divergence in the primary (103 of 109 individuals) mt clade and, with one minor exception, they appeared fixed for a single nuclear ITS-2 genotype. Although complicated by the presence of rare, highly divergent mt lineages (of either introgressive or persistent ancestral polymorphic origin) in some populations, the molecular data were consistent with a taxonomic conclusion that these five nominal taxa represent a single polymorphic lineage of the type species L. fuscus. AMOVA analyses indicated that 56% of the observed mt variation could be attributed to among population differences, only two of 36 haplotypes were detected in more than one sampling location, and estimates of among-population mt gene flow were generally low at both regional and continental scales. Unrooted network analyses revealed a number of mt tip clades, one restricted to the southwestern part of the range, the remainder having overlapping distributions in eastern North America. All of the eastern tip clades occurred in the Mid-Atlantic region, and these samples displayed by far the highest levels of collective mt diversity. However, directional gene flow estimates indicated that this region has been a recipient (especially from Alabama populations), rather than a source of haplotypic diversity, implying that it likely represents a center of overlap, not a primary ice age refugium, for this limpet species.