Biochemical variation and shell shape in populations of the fresh-water snail Lymnaea peregra (Mollusca, Gastropoda, Pulmonata) from south-west Ireland

Lymnaea peregra was collected at sites, predominantly from the Caha plateau, in south-west Ireland. These included sites investigated by previous workers and found to contain populations with a distinctive pattern of variation in shell-shape. Normally spired populations and non-spired ( involuta, sub-involuta ) could occur in adjacent loughs in the same watershed. The biochemical variation in some of these populations was investigated using horizontal starch-gel zone electrophoresis. Fourteen biochemical loci were investigated. Although circumscribed by difficulties in collecting and low sample numbers, the investigation showed that the pattern of variation in shell shape was still present and was not correlated or associated with the biochemical variation. While this did not support hypotheses of geographic race formation or incipient speciation, it was in agreement with the current view of variation and speciation in fresh-water pulmonates.     

Allozyme and morphology evolution in European Viviparidae (Mollusca: Gastropoda: Architaenioglossa)

The paper describes morphometric and allozymic differences among four European species of the family Viviparidae: Viviparus contectus (Millet, 1813), V. viviparus (Linnaeus, 1758), V. acerosus Bourguignat, 1862, and V. ater (Cristofori et Jan, 1832). Fourteen continuous biometrical characters were measured. Incremental discriminant-function analysis, principal-component analysis, and non-metric multidimensional scaling were applied to analysis of the morphometric differences. All the techniques confirmed a similar picture: a slight morphometric differentiation, with the variability ranges of the species overlapping. On the other hand, the allozymic differentiation, studied at 12 loci, eight of them intra and/or interspecific polymorphic, is much better marked, the intraspecific Nei's distances among the four V. contectus populations ranging from 0.0014 to 0.0397, mean 0.0166, and interspecific distances ranging from 0.2306 (V. ater–V. acerosus) to 0.9888 (V. contectus 2 and V. viviparus), mean 0.6871. The allele frequencies and genetic distances (Nei's distance and Cavalli-Sforza and Edwards’chord distance) were used to compute maximum likelihood, additive Fitch–Margoliash and ultrametric Fitch–Margoliash trees. All the trees presented a similar pattern, but the maximum-likelihood and additive trees, based on Cavalli-Sforza and Edwards’distance, seem to reflect the phylogeny best. The results are compared with the most parsimonious phylogenies inferred for radular, soft-part morphology and anatomy, and opercular data from other papers by us, and the inferred phylogenies are also compared. Although the inferred molecular and morphological phylogenies are little different in topology, the amount of evolution along the corresponding branches (measured as the number of changes averaged over all reconstructions) is very different, the value of correlation coefficient between the two phylogenies being statistically insignificant. The occurrence of interspecific hybrids is discussed, and the isolation-by-competition mechanism is postulated. The probable origin of V. viviparus from a founder population extremely restricted in number is stressed. The possible history of the group is briefly discussed. The species is suggested to have originated in an unusual habitat of melt water at a glacier foreland that could have promoted genotypic differentiation and sympatric speciation.     

A photoperiod gene regulates vitellogenesis in Lymnaea peregra (Mollusca: Gastropoda: Pulmonata)

Summary

Populations of the fresh-water snail Lymnaea peregra from different localities vary in their capacity to lay eggs, responding either to long day or to short day photoperiods. These responses are genetically determined by a single gene locus with the long day allele dominant over the short day allele. Although previtellogenic stages of oogenesis are not affected by an inhibitory photoperiod, vitellogenesis is essentially shut down. The volumes of the dorsal bodies, which are endocrine organs that mediate vitellogenesis, are significantly smaller in snails maintained in an inhibitory photoperiod. Implantation of cerebral ganglia with attached dorsal bodies, both from egg laying animals and from dormant animals that have the potential to lay eggs in the postoperative photoperiod, into snails that were inhibited by insufficient photoperiod resulted in a significant increase in vitellogenesis in the ovotestes of the hosts. An increase in host dorsal body volume was also observed. The photoperiod gene appears to control some aspect of the cerebral ganglion that activates the dorsal body to produce a hormone that stimulates vitellogenesis in the ovotestes. Photoperiodic control of reproduction may be a factor contributing to the diverse life history strategies observed in this species.     

On the occurrence of Lymnaea auricularia (Gastropoda: Lymnaeidae) in New Zealand

Abstract

The occurrence in New Zealand of Lymnaea auricularia (L.) is recorded for the first time, and its status world-wide is briefly discussed, with particular reference to its role in economic parasitology. The lymnaeid fauna of New Zealand is briefly reviewed.     

Synonymy between Lymnaea bogotensis Pilsbry, 1935 and Lymnaea cousini Jousseaume, 1887 (Gastropoda: Lymnaeidae)

The lymneid snail Lymnaea bogotensis Pilsbry 1935 is synonymized with L. cousini Jousseaume 1887, based on morphological comparisons of the reproductive systems. The shell, renal tube, and reproductive system are described and illustrated from specimens collected in the type locality and the municipality of Paipa, Colombia. Bibliographical records reveal L. columella to be the commonest lymneid in the country. The latter two species can be differentiated based on the morphology of the penial complex.     

Intraspecific life-history variation in Radix plicatulus (Gastropoda: Pulmonata: Lymnaeidae)

Life-histories of Radix plicatulus (Benson, 1842) populations inhabiting two neighbouring sites on a Hong Kong stream were investigated. In one of the two sites, R. plicatulus co-occurred with high densities of Pomacea levior which is known to prey on the egg capsules and hatchlings of sympatric gastropods. On the basis of general life-history theory, I hypothesized that R. plicatulus which co-occurred with P. levior should exhibit a life-history strategy characterized by a delayed reproduction, a longer recruitment period and a larger number of breeding bouts per year as compared with contemporaries inhabiting the other site with low P. levior abundance. Reproductive patterns of the two populations observed in the field accorded with the expectations of general life-history theory, and lent support to the hypothesis. However, laboratory culture experiments revealed no evidence of a genetic basis for the interpopulation differences. The importance of establishing a genetic basis for the interpopulation divergence before invoking an evolutionary explanation was discussed.     

First record of the freshwater snail Pseudosuccinea columella (Gastropoda: Lymnaeidae) in southern Pampas (Argentina) and assessment of future spread

ABSTRACT

The freshwater snail Pseudosuccinea columella was recorded for the first time in Argentina more than 60 years ago. Since then its distribution in the wild has been restricted to the northeastern provinces. Here we record the presence of P. columella in southern Pampas for the first time, extending its distribution more than 500?km southwards. The climatic suitability of this and other areas of South America for its establishment and spread was analysed using habitat modelling software. Hitherto its spread within and between watercourses in southern Pampas has been very limited, probably through a combination of low climatic suitability, recent introduction and low connectivity of the drainage basins. The suitability of other areas where it has been recently recorded indicates a moderate risk of further spread in central and northwestern Argentina and in coastal areas of the Pacific rim of South America (southern Perú and northern Chile). The recent spread of P. columella in the wild in Argentina may be the result of an increase in the trade in aquarium plants or of the evolution of a new lineage with different ecological capabilities.     

Effect of the exposure to Fasciola hepatica (Trematoda: Digenea) on life history traits of Lymnaea cousini and Lymnaea columella (Gastropoda: Lymnaeidae)

The snails Lymnaea columella and Lymnaea cousini have both been reported as intermediate hosts of Fasciola hepatica in Colombia. The effect of the exposure to the parasite on survival, fecundity and size of these snails was evaluated by means of experimental infections and the life history traits of control and exposed groups were compared. Infection rates were 82.2 and 34% for L. columella and L. cousini, respectively. A reduction in fitness was observed in both species when exposed to the parasite: fecundity alone was reduced in L. columella whereas in L. cousini there was also a decline in survival rate. Unlike other studies, increased size was not observed in either species. On the contrary, a reduction in growth rate was observed in L. columella.     

An examination of the marsh microhabitats of Lymnaea tomentosa and L. columella (Mollusca: Gastropoda) by path analysis

Some physical and biological characteristics of marsh microhabitats of the pulmonate snails Lymnaea tamentosa (Pfeiffer) and L. columella (Say), intermediate hosts of Fasciola hepatica in New Zealand, are compared by path analysis. The most significant variable suggested by the various path coefficients is the relative importance of flocculence of mud in the substratum. L. tomentosa was more likely to be found in or on flocculent mud, whereas L. columella appeared to prefer firm mud. Submersion of the substratum was of more direct importance to L. columella than to L. tomentosa; the effect of water on L. tomentosa was mainly indirect, since wetter microhabitats were more likely to contain flocculent mud. Results of an experiment simulating pugging of the muddy substratum by cattle suggest that both snail species are likely to be more numerous in habitats heavily pugged by cattle.     

A new late Miocene Lymnaea with aberrant suture structure unique for the family (Gastropoda: Pulmonata: Lymnaeidae)

A new fossil species of the pond snails (family Lymnaeidae Rafinesque, 1815), Lymnaea bogatschevi sp. n., from the Neogene (Khersonian–Maeotian transition) of southern Russia is described. It is characterised by a peculiar structure of the shell suture not found elsewhere in the family Lymnaeidae (both in living and extinct taxa). The suture of L. bogatschevi sp. n. may be described as a narrow groove that penetrates deep into the shell matter. This feature is developed both in protoconch and teleoconch whorls and is presented in several 100s of specimens that precludes its origin as an individual abnormality. There are no environmental factors known to induce such groove-like sutures in aquatic pulmonates indicating a genetic basis for this structure in L. bogatschevi. Also, we report a single shell with the similar channelled suture from a sample of Lymnaea megarensis (Gaudry in Fischer, 1867) from the Pliocene of Greece. It seems, in this species the groove-like suture was represented as a rare individual aberration, and later this trait disappeared completely from the lymnaeid morphological repertoir. Possible phylogenetic relationships between L. bogatschevi and the recent L. (Kazakhlymnaea) taurica (Clessin, 1880) are suggested and briefly discussed.     

Molecular and morphological divergence in the butterfly genus Lycaeides (Lepidoptera: Lycaenidae) in North America: evidence of recent speciation

Male genital morphology, allozyme allele frequencies and mtDNA sequence variation were surveyed in the butterfly species Lycaeides idas and L. melissa from across much of their range in North America. Despite clear differences in male genital morphology, wing colour patterns and habitat characteristics, genetic variation was not taxonomically or geographically structured and the species were not identifiable by either genetic data set. Genetic distances (Nei's D=0.002–0.078, calculated from allozyme data) between all populations of both species were within the range commonly observed for conspecific populations of other butterflies. The most frequent mtDNA haplotype was present in individuals of both species in populations from southern California to Wisconsin. We conclude that speciation has probably happened recently and the lack of genetic differentiation between the species is the product of either (1) recent or ongoing gene flow at neutral loci, and/or (2) an insufficiency of time for lineage sorting. The evolution of male genital morphology, wing colour patterns and ecological characteristics has proceeded more rapidly than allozyme or mtDNA evolution.     

Hybridization studies of Haemonchus contortus (rudolphi, 1803) and H. placei (place, 1893) (Nematoda: Trichostrongylidae)

Hybridization experiments between Haemonchus contortus from sheep and H. placei from cattle indicate that the H. placei vulvar morph type and the inability of the eggs to hatch and develop at 11°C were inherited as dominant traits in the hybrids. The size of the third stage larvae was similar to H. placei in hybrids from the mating of male H. placei × female H. contortus while larvae from the reciprocal mating were intermediate in size. Hybrids produced by the mating of thiabendazole resistant female H. contortus × non-resistant male H. placei were also resistant. The F₁ males of the mating between male H. contortus and female H. placei were sterile. Male sterility did not occur in the reciprocal cross until the F₂ generation. Female hybrids from these generations had a low level of fertility when backcrossed to males of either parent species. Cytological studies of the hybrid males indicated that sterility was due to several kinds of meiotic disturbance and that spermatogenesis stopped during metaphase I. The chromosomes in eggs of unfertilized females did not undergo meiosis and polar body formation; instead they increased in number by a process of endomitosis. Unfertilized eggs in the faeces were characterized by uneven cytoplasmic division and abnormal shape. It is proposed that hybrid sterility can lead to the local eradication of one species of Haemonchus by the other. Furthermore, the outcome of which species is eradicated can be influenced by such variables as initial population sizes, climate, and the local ratio of sheep to cattle.     

In vivo efficacy of praziquantel against Echinoparyphium aconiatum (Trematoda: Echinostomatidae) parasitizing the great pond snails Lymnaea stagnalis (Gastropoda: Lymnaeidae)

The present study had a practical goal. I aimed to determine whether praziquantel could reduce the production of Echinoparyphium aconiatum (Trematoda: Echinostomatidae) cercariae in infected snails Lymnaea stagnalis (Gastropoda: Lymnaeidae) without killing the hosts. Praziquantel is a broad-spectrum antihelminth agent. It caused a total cessation of cercaria shedding when the praziquantel concentration in the treatment bath was 10 mg/L and the treatment time was 30 h or longer. A next research step which has to be taken before giving detailed recommendations about using praziquantel for ceasing production of E. aconiatum cercariae in parasitized snails is to follow the survivorship and performance of treated snails after a praziquantel exposure for longer than in this medium-term (3 days) experiment.     

Red kite (Milvus milvus) and black kite (M. migrans): minute genetic interspecies distance of two raptors breeding in a mixed community (Falconiformes: Accipitridae)

Allozyme analysis of 24 loci in 154 red kites (Milvus milvus) and 36 black kites (Milvus migrans) from die Hakel forest (Sachsen-Anhalt, Germany) revealed a Nei's interspecies genetic distance of D = 0.009. Of die observed genetic variance of four polymorphic enzymes, 15.4% referred to die differentiation between die kite species, but 84.6% were contributed by the ingroup polymorphism widiin diese species. Allozymes permit the identification of some 78% of samples as orignating from M. milvus , but only of 5.4% of samples obtained from M. migrans. Akhough the genetic distance is slight, die Milvus kites are valid biospecies which, despite occasional instances of hybridization, coexist sympatrically and may breed in mixed breeding aggregations. Mate choice in die largely separate winter quarters of diese migratory birds or chromosomal incompatibility are hypodietical isolation mechanisms stabilizing die species boundary. Moreover, the range sympatry could have developed fairly recendy widi die spread of human agriculture.     

Subdivided population structure and phylogeography of an endangered freshwater snail, Notopala sublineata (Conrad, 1850) (Gastropoda: Viviparidae), in Western Queensland, Australia

Populations of the Australian freshwater snail Notopala sublineata (Conrad, 1850) have declined rapidly over the last decade, but are still abundant in most river systems of Western Queensland. These rivers are characterized by the unpredictable and highly variable nature of their climatic and hydrological regimes, with episodic periods of very large flow and many periods of little or no flow. We used mitochondrial sequences and allozymes to investigate the genetic structure and infer patterns of dispersal of N. sublineata within this unique environment. We sampled 24 waterholes throughout the four major catchments of the Lake Eyre Basin. Based on a 457-bp fragment of the mitochondrial cytochrome oxidase subunit I gene, we identified 55 haplotypes in a sample of 256 individuals. Both nuclear and mitochondrial genetic datasets indicated high levels of genetic subdivision and restricted gene flow among populations within and among catchments. The mitochondrial haplotypes clustered into two main geographical clades, corresponding with two groups of adjacent catchments: Cooper–Bulloo and Diamantina–Georgina, which appear to have diverged 300 000 years ago. Populations of N. sublineata within these adjacent catchments seem to have diverged relatively recently, roughly 130 000 years ago. Contemporary dispersal seems to be absent between catchments but we suggest that climate fluctuations during the Pleistocene resulted in extensive floods that promoted historical movement of aquatic organisms across catchment boundaries.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 1–16.     

Life on the edge: a hybrid zone in AZbinaria hippolyti (Gastropoda: Clausiliidae) from Crete

The hybrid zone between the Greek land snails Albinaria hippolyti aphrodite and Albinaria hippolyti harmonia runs exactly along the edge of a gorge. At two localities, we analysed patterns of variation in three enzyme loci, six conchological characters, and two anatomical characters across the zone. Clines in the various characters are largely coincident and concordant. They are narrow (approximately 30 m wide) where the ecological transition is abrupt, and wider (approximately 120 m wide) where a valley cuts into the gorge, making the environmental change more gradual. In spite of the obvious correlation with an ecological transition, we do not believe the zone is maintained by a selection gradient. Instead, direct and indirect evidence for hybrid disadvantage and evidence for directional dispersal at the edge of the gorge suggest that it is a tension zone, held at the ecotone by differential dispersal of at least one of the parental types. We speculate on the possibility that reinforcement may act in the hybrid zone. Our data on dispersal and reproductive isolating mechanisms lead us to believe that reinforcement may only be possible at localities where the hybrid zone is very narrow.     

Genetic differentiation and speciation in Stomion (Goleoptera: Tenebrionidae): flightless beetles of the Galápagos Islands, Ecuador

Stomion is a swarm of 13 tenebrionid beetle taxa endemic to the Galápagos Islands. The taxa show marked morphological variation, and all are flighdess. They can be divided into three divergent morphological groups based on external sculpturing of the elytra. Eleven taxa were examined electrophoretically at 20 enzyme loci to measure the extent of genetic differentiation which accompanied morphological differentiation and speciation. Stomion are shown to be ideal candidates for allopatric and founder event speciation, with their limited dispersal ability, narrow distributions, and incidence of single-island endemics. Accordingly, individual heterozygosities were low in most taxa, and gene pool divergence was apparent among populations of single taxa occupying different islands. Both interspecific and intraspecific genetic identities were high, with an average 1 = 0.88 and I = 0.96, respectively. The relatively young age of the genus and the allopatric mode of speciation may account for high genetic relatedness. No clear relationship was found between allozyme phenotypes and the three morphological groups, thus, the evolution of these traits may have been facilitated by similar selection among islands of similar age and geography. The geographical distributions of the morphological groups can be used to suggest a general pattern of speciation for the group.