Search

Populations of the polymorphic land snail Cepaea nemoralis ( L.) from Deepdale, Derbyshire, UK, sampled in 1965-67, showed a pattern of area effects, with steep clines among groups of populations differing in shell colour and banding morph frequencies. In 2010, most of these populations were resampled. In particular, a continuous transect made in 1967 of 42 quadrats (18.34 × 18.34 m) across a steep cline in several morph frequencies was completely resampled. In the dale as a whole, yellow shells had increased in frequency. In the transect, the frequencies of banding morphs showed no significant changes, although colour morphs showed some changes. Pink shells had increased in frequency in a section in which scrub had developed, and brown shells had increased in frequency in the area in which they had originally been at the highest frequency. In each case, the selection coefficients were of the order of 4%. Yellow had increased elsewhere. Nevertheless, both in the dale as a whole and in the transect, the pattern of geographical change in morph frequencies had remained essentially the same. Estimates of migration based on previous studies of marked snails and on modelling of the effect of drift and migration suggest that, regardless of whether the cline is a product of differential selection or of the gradual merging of previously separate founding populations, it has been in existence for a long time, and that migration occurs over greater distances than estimated from direct observation on marked snails. Although we can demonstrate that selection has occurred, the origin and maintenance of the cline and others similar to it remain in doubt; the development and maintenance of polymorphism in this species may require consideration of several processes operating on different time scales. © 2012 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Changes in morph frequency over time in sand-dune populations of Cepaea nemoralis in the British Isles have been examined using the Evolution Megalab database. Frequencies in colonies on a sand dune at Berrow, Somerset were estimated in 2008-9. This extends a survey started in 1926 by A. E. Boycott and C. Diver and continued in the mid-20th Century by B. C. Clarke and J. J. Murray. An increase in the frequency of the mid-banded morph, noted in earlier work, has continued. The apparent decrease in brown was not confirmed but the yellow frequency has increased. At a range of dunes in the British Isles, comparisons between data from the mid-20th Century and the early 21st Century indicate an increase in yellow and mid-banded morphs and a decrease in banding and brown morphs. These results differ from the overall trends derived from Europe-wide comparison of early data with Evolution Megalab data, in which banded and mid-banded increased in frequency, whereas there was no overall change in yellow. The general pattern of regional variation has been retained, although there is also high heterogeneity between samples, suggesting that a variety of factors are involved in explaining the changes. The mean shifts in frequency are consistent with climatic change over the period. Dunes are probably the most likely habitat in which to detect such a change. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 108, 315-322. [ABSTRACT FROM AUTHOR]

Fruticicola fruticum (O. F. Müller, 1774), a medium-sized helicoid snail in the Camaenidae, has a wide range in Europe, reaching from the Urals and the Caucasus to the Balkans, and from the southern part of Scandinavia, through Central Europe to eastern and central France and northern Italy. There are numerous studies on its distribution, biology, life cycle, etc., but little is known about the genetic diversity of this taxon. Here, we studied the phylogeny and phylogeography of F. fruticum using two mitochondrial markers: cytochrome oxidase subunit I (COI) and 16S ribosomal RNA (16S); and four nuclear markers: 18S ribosomal RNA (18S), 28S ribosomal RNA (28S), internal transcribed spacer (ITS-2), and histone 3 (H3). The study was based on 59 populations sampled across the range. Whereas nuclear markers showed little differentiation, phylogenetic analysis of COI sequences clearly confirmed the distinctness of the European Fruticicola and Asian Bradybaena (p-distance 0.229). Within Fruticicola 54 haplotypes were detected, haplotype diversity (Hd) = 0.973 ± 0.006, nucleotide diversity (π) = 0.137 ± 0.005. ABGD and PTP delimitation analyzes distinguished eight mOTUs. Two sequences (our mOTU C) from Russia were published in the GenBank as two distinct species: F. schrenckii and F. transbaicalia. Seven further mOTUs identified in our study formed three distinct lineages, regarded as species. The first (mOTU A and mOTU B), represented by 40 populations, occupies a wide range across northern and central Europe, extending east to Ukraine and south to northern Croatia (mOTU B). It encompasses the type locality of F. fruticum, and can be recognized as F. fruticum sensu stricto. Another lineage (mOTU D and mOTU E), represented by six populations in central Romania, appears to form another species. Both mOTUs were found together in one population. A third lineage, containing mOTUs F, G and H, represented by 14 populations, was distributed across the Balkans from N.E. Croatia to Bulgaria. p-distances between the three species ranged from 0.172 to 0.219, and between all the mOTUs, pooled together, from 0.172 to 0.258. The highest genetic diversity was found in species 3 (0.112) and the lowest in species 1 (0.025), despite its largest geographic distribution. Pairwise p-distances, Tamura 3-parameter distances, composite likelihood distances, as well as the coancestry coefficient F ST , calculated for all populations pooled together were significantly associated with geographic distance, but this was not the case within each of these three species. The significant association for all populations reflected high diversity between the species coupled with high geographic distances between their populations, not the character of intraspecies diversity. With a few exceptions, there hold a rather infinite island model with low migration. AMOVA detected 78% of the variance between the three species, 18% among populations within the species, and only 3.6% within the populations. The low genetic diversity of widespread F. fruticum s. stricto, compared with much higher diversity of two narrowly distributed newly found species of Fruticicola, may reflect the rapid spread of the former into previously uninhabitable regions, while the latter were able to maintain populations in glacial refugia. The estimated time of divergence between the three species, 1.7-2.19 mya, suggests their ancestors' isolation in southern European refugia during the lower Pleistocene, the Gelasian/Calabrian. There was no clear association of variation in shell morphology and lineage or mOTU identity; on external characters, these species are semicryptic, subtle differences in reproductive anatomy among them were found., (Copyright © 2022 Elsevier Inc. All rights reserved.)