Epiphallus anatomy in the Arion hortensis species aggregate (Mollusca, Pulmonata)

A SEM study of the structure associated with the outlet of the epiphallus in the atrium genitale of three arionid species ( Arion hortensis s.s., A. distinctus and A. owenii ) is presented. The structures are described and compared, and the specific differences are outlined. Preliminary notes on the same structure in A. intermedius , as well as on the spermatophores of A. hortensis s.s. and A. distinctus , are also provided. It is concluded that A. owenii stands somewhat apart in relation to the latter two species, since it may be more related to A. intermedius. Although it is generally accepted that the genus Arion is characterized by the absence of a penis, it is suggested here that the described structure at the outlet of the epiphallus is nothing but a remnant of an ancestral penis; anyhow, it is at least functionally allied to a penis.     

A comprehensive phylogeographic study of Arion vulgaris Moquin-Tandon, 1855 (Gastropoda: Pulmonata: Arionidae) in Europe

Organisms Diversity & Evolution - Arion vulgaris Moquin-Tandon, 1855 is regarded as one of the 100 most invasive species in Europe. The native distribution range of this species is uncertain,...     

Genital and allozyme similarity between Arion urbiae and A. anguloi (Mollusca: Pulmonata)

A comparison of the genital features of Arion urbiae and A. anguloi suggests that the species are extremely similar, if not identical. This hypothesis is supported by an electrophoretic analysis of 13 putative enzynme loci, which shows that the two species are also genetically yery similar (I = 0.947), while the related A. subfuscus consists of two distinct genetic types (I = 0.421). These results are further confirmed by a study of esterase profiles obtained with isoelectric focusing. It is therefore concluded that A. urbiae and A. anguloi are most probably conspecifie, whereas the genetic types of A. subfuscus may represent two different species.     

The genetic dynamics of the rapid and recent colonization of Denmark by <Emphasis Type="Italic">Arion lusitanicus</Emphasis> (Mollusca,Pulmonata, Arionidae)

We describe the genetic dynamics of the recent establishment of the ‘Iberian slug’, Arion lusitanicus J. Mabille 1868, in Denmark and compare its population structure to two other members of the ‘large Arion complex’, Arion ater ater, native to Denmark, and Arion ater rufus, introduced into Denmark in the early 1900s. Assaying allozyme polymorphism at seven enzyme loci, we found that: (1) None of the three taxa reproduce primarily by self-fertilization. Differences among loci and colonies in the pattern of deviation from Hardy–Weinberg equilibrium are most consistent with isolate mixing and perhaps with low amounts of selfing. (2) For both A. lusitanicus and A. a. rufus, gene diversity is lower in Danish colonies than in southern German colonies, implying population bottlenecks in the establishment of Danish colonies. (3) Significant linkage disequilibrium values usually involve the same three loci, viz. PGI, MDH-1 and MDH-2, suggesting physical linkage among these loci. (4) For both A. a. rufus and A. lusitanicus, the overall gene frequencies from Denmark and southern Germany are homogeneous, while variation among colonies within these regions ranges from around 15 to 28% for the three taxa. This indicates strong, local population genetic subdivision but with little restriction to gene flow from possible source areas. The heterogeneity in measures of diversity and differentiation indicates that population structure for all three taxa is dominated by ongoing founder effects, local extinction/colonisation dynamics, and genetic drift processes.     

Population Genetics and Identity of an Introduced Terrestrial Slug: Arion subfuscus s.l. in the North-east USA (Gastropoda, Pulmonata, Arionidae)

Several European species of the terrestrial slug genus Arion have been introduced into North America. A case in point is the species complex A. subfuscus s.l. which has become one of the most abundant slug taxa in North America. In Europe this complex consists of at least two cryptic species, viz. A. fuscus and A. subfuscus s.s., the latter of which is further subdivided in five strongly divergent mtDNA lineages (A. subfuscus S1–S5). In order to determine which of these A. subfsucus s.l. taxa are present in the NE USA and in order to assess their population genetic structure, we compared mtDNA, nDNA and allozyme variation between populations from the NE USA and Europe. Our results show that (1) at least A. subfuscus S1 has become successfully established in the NE USA, (2) founder effects are the most likely explanation for the loss of a large amount of molecular genetic variation in populations from the NE USA (i.e. a loss of 96% of the 16S rDNA haplotypes, 67% of the ITS1 alleles and 46% of the alleles at polymorphic allozyme loci), and (3) part of the remaining genetic variation in NE USA populations was probably due to multiple introductions from the British Isles and the European mainland, and the hybrid structure of most of these source populations. Apparently, the extreme loss of molecular genetic variation in this introduced species has not prevented it from successfully establishing and spreading in novel environments.     

The taxonomy of two host-specific, cryptic dendronotoid nudibranch species (Mollusca:Gastropoda) from Australia including a new species description

Two host-specific, extremely cryptic, small dendronotoid nudibranchs from Australia are described and classified, and their phylogenetic position within the superfamily is discussed- Lomanotus vermiformis Eliot, 1908 subsists exclusively on the hydrozoan Lytocarpus philippinus (Kirchenpauer, 1872). Lomanotus stauberi Clark & Goetzfried, 1976 is newly synonymized with L. vermiformis . Marioniopsis platyctenea sp. nov. subsists exclusively on the alcyonacean Parerythropodium hicksoni Utinomi, 1972. Marianina rosea (Pruvot-Fol, 1930) is relocated to the Tritoniidae (wherein it forms a monotypic subfamily, Marianinae) because of possession of palmate rhinophoral clavi, the principal apomorphy of the Tritoniidae. The validity of using the form of the digestive gland as a basis for dividing the Tritoniidae is questioned since it is acknowledged that this organ has progressed from a solid (holohepatic) arrangement to a dispersed (cladohepatic) arrangement in parallel in several major nudibranch lineages; form thus offers merely homoeoplaseous phylogenetic characters. Separation of right and left digestive glands appears to be one of the first steps in the simultaneous and interdependent evolutionary processes of internal detorsion and external 'aeolidization' in nudibranchs.     

Assessment of the genetic distances between some species of the family Bradybaenidae (Mollusca,Pulmonata)

On the basis of inter-simple sequence repeat (ISSR) loci and the nucleotide sequences of nuclear (18S and ITS-1) and mitochondrial genes (COI and 16S), a phylogenetic analysis of the three species of terrestrial mollusks of the family Bradybaenidae (Mollusca, Pulmonata), Bradybaena fruticum Müll., Bradybaena schrencki Midd., and Bradybaena transbaicalia Shileyko, was conducted to clarify their taxonomic status. The analysis showed that Br. fruticum was far apart from the other two species (Br. schrencki and Br. transbaicalia). The genetic distance between the latter puts in doubt their status as distinct species. It is suggested that the species Br. transbaicalia can be treated as a form of Br. schrencki var. transbaicalia.     

An electrophoretic characterisation of three paratypes of Arion fagophilus De Winter, 1986, with notes on the subgeneric division of the genus Arion Férussac, 1819 (Mollusca, Pulmonata)

Three paratypes of Arion fagophilus were electrophoretically compared with nine other West European species of the genus Arion. Esterases, glutamate-oxaloacetate-transaminase, a-amylase, superoxide dismutase, phosphoglucomutase, fumarase, α-glycerophosphate dehydrogenase and phosphogluconate dehydrogenase were screened in the hepatopancreas and general proteins in the albumen gland. A. fagophilus appears to be a very well defined species, which may be assigned to the subgenus Kobeltia. The subgeneric division of the genus Arion is preliminary discussed with respect to electrophoretic and chromosomal data. It is concluded to retain four subgenera, which may be grouped two by two: Mesarion and Arion s. s. on one hand, and Kobeltia and Carinarion on the other. It is remarked that the electrophoretic differences between Norwegian and Belgian A. ater suggest a separation into two taxa.     

Ultrastructure of the osphradium of Siphonaria grisea (Mollusca, Pulmonata)

By means of scanning and transmissive electron microscopic methods osphradium of Siphonaria grisea has been studied. The osphradium of the animal is presented as a small torulus formed by supporting ciliated cells. Among them bodies of receptory cells are situated; they are of smaller size and decorated with a bundle of microvilli. Central processes of the receptory cells, penetrating through a thick layer of the connective tissue, reach the subepithelial neural trunk. Concentration of the neural cells in the periphery of the trunk is small, and in the central area no chemical synapses are revealed. The data presented demonstrate a primitive structure of the osphradial chemoreceptory organ in Siphonaria.     

Extreme mtDNA divergences in a terrestrial slug (Gastropoda, Pulmonata, Arionidae): accelerated evolution, allopatric divergence and secondary contact

Extremely high levels of intraspecific mtDNA differences in pulmonate gastropods have been reported repeatedly and several hypotheses to explain them have been postulated. We studied the phylogeny and phylogeography of 51 populations (n = 843) of the highly polymorphic terrestrial slug Arion subfuscus (Draparnaud, 1805) across its native distribution range in Western Europe. By combining the analysis of single stranded conformation polymorphisms (SSCP) and nucleotide sequencing, we obtained individual sequence data for a fragment of the mitochondrial 16S rDNA and a fragment of the nuclear ITS1. Additionally, five polymorphic allozyme loci were scored. Based on the 16S rDNA phylogeny, five monophyletic haplotype groups with sequence divergences of 9-21% were found. Despite this deep mitochondrial divergence, the haplotype groups were not monophyletic for the nuclear ITS1 fragment and haplotype group-specific allozyme alleles were not found. Although there is evidence for an accelerated mtDNA clock, the divergence among the haplotype groups is older than the Pleistocene and their current allopatric ranges probably reflect allopatric divergence and glacial survival in separate refugia from which different post-glacial colonization routes were established. A range-overlap of two mtDNA groups (S1 and S2, 21% sequence divergence) stretched from Central France and Belgium up to the North of the British Isles. The nuclear data suggest that this secondary contact resulted in hybridization between the allopatrically diverged groups. Therefore, it seems that, at least for two of the groups, the deep mtDNA divergence was only partially accompanied by the formation of reproductive isolation.     

Differentiation of large arionid slugs (Mollusca, Pulmonata) using ligula morphology

A study of the ligula (a holdfast/stimulatory device associated with the distal genitalia) in the species aggregates Arion ater and A. lusitanicus, common in NW Europe, suggests that examination of this organ may permit rapid and reliable differentiation to the sub-specific level. This study describes the ligula and its taxon-specific characteristics, illustrated by three-dimensional stereo photographs, which clearly reveal its structure and can be readily compared with dissected material. The bizarre and intricate variations some taxa exhibit in the form of this organ are interpreted in terms of mating behaviour.     

Biology of slugs (Agriolimacidae and Arionidae: Mollusca) in New Zealand hill country pastures

Summary Life cycles of the slugs Deroceras reticulatum and Arion intermedius were studied over a 2.5-year period in a sheep-grazed pasture in the Kaimai Range, New Zealand. D. reticulatum approximated a bivoltine phenology, with intervals between consecutive generations ranging from 4 to 7 months and maximum life span from 8 to 12 months. Egg laying occurred in autumn and spring-early summer. Periods of egg hatching were followed by a phase of juvenile growth characterised by linear increase in the logarithm of population mean body weights. This was followed by a phase of reproductive activity. A. intermedius had an annual life cycle. Eggs laid during late summer and autumn hatched during autumn-winter. Immature slugs were characterised by a period of low growth rate during winter followed by a period of rapid growth culminating in reproductive maturity. In both species, the phase of rapid growth rate was associated with enlargement of the hermaphrodite gland. The size of the hermaphrodite gland relative to body weight reached a maximum during the spermatozoon stage, generally coincident with maximum body weight. During the reproductive period of D. reticulatum and A. intermedius the body weight remained relatively stable but the hermaphrodite gland became progressively smaller as the slugs approached the post-reproductive stage. The albumen gland attained maximum weight at the oocyte stage of the hermaphrodite gland, at the onset of reproductive activity. The pasture, strongly dominated by grasses, was heterogenous in slope, vegetation and treading/grazing influences from sheep due to stratification of the habitat into contour tracks, associated with sheep movement around the slope contours, and intertrack areas. High population densities of D. reticulatum were associated with the track edges (kerbs) and the upper intertrack slopes, while densities of A. intermedius were highest for the intertrack slopes. Low densities of both species occurred on the tracks and at sheep campsites. Analysis of cohort life tables indicated that these dispersion patterns were important in the dynamics of the populations. The stage mortality contributing most to the variance in reproductive populations of both species was that between hatching and onset of reproduction; most of the mortality occurred shortly after hatching on south-facing slopes, but tended to occur later in the life cycle on north slopes. For D. reticulatum this mortality was inversely related to initial density and associated, at least in part, with predation by carabids and birds and with treading by sheep. Density relationships, both at whole plot and plot stratum level, indicated that variations in natality had a stabilizing influence on D. reticulatum populations.