Radiation of the land snail genus Sagda (Pulmonata: Sagdidae): comparative morphology, biogeography and ecology of the species of north-central Jamaica

The radiation of the endemic Jamaican land snail genus Sagda is examined through analysis of the comparative shell morphology, anatomy, ecology and biogeography of the four species inhabiting north-central Jamaica: S. centralis sp. nov. , S. spei, S. bondi and S. montegoensis. The species are all rather similar in their morphology and ecology. The shells show some differences in the presence or absence of internal lamellae, the position of the lamellae, the form of the depression in the centre of the base, the regularity of sculpture (low ribs) and the pattern of microsculpture. Slight differences in the form of the radular teeth are found between some species. The structure of the secondary ureter is peculiar: in all species it is open shortly behind the mantle collar, then branches into two closed tubes which open separately on the outside of the mantle collar. Despite its great complexity, the reproductive system is rather uniform among species; differences are seen in the number of pockets that form spines on the spermatophore. The complex, three-branched spermatophore is formed within the entire epiphallar branch of the penis, whereas the appendicular branch apparently assumes the copulatory function. When inactive, all species are found associated with rocks or, less commonly, among leaf litter. Activity occurs primarily at night and mostly on leaf litter rather than rocks. The snails eat dead plant material, including a variety of plant species. All species (with the possible exception of S. montegoensis) are ovoviviparous. They overlap broadly in the range of climates occupied. The geographic ranges of the four species are overlapping, although Sagda bondi has a parapatric distribution in relation to the western species S. grandis. Fossil and subfossil evidence shows that shifts in the ranges of the species have occurred in the late Quaternary; Pleistocene-Holocene environmental changes, habitat destruction by man, and possibly other environmental changes during historical times are probably involved. Radiations of other land snail groups on tropical islands have generally produced greater morphological and ecological differentiation than in Sagda. Allopatric or parapatric species distributions appear to be more common in other land snail radiations.     

Annotated type catalogue of land snails collected from Taiwan (Formosa) in the Natural History Museum,London

The present catalogue lists the type specimens of land snail species, collected from Taiwan and deposited in the Natural History Museum, London. Thirty-seven nominal species described by Pfeiffer, Adams, Nevill, Moellendorff, Godwin-Austen and Gude were traced. I present here information on type status, collection data obtained from the registers and labels of each collection, and annotations on the current taxonomic affiliation. Lectotypes of 28 nominal (sub)species were newly designated. One holotype was fixed originally and two holotypes newly fixed by monotypy. Syntypes of two species and paralectotypes of three species were also discovered in the Museum. No specimen of the species Pupina adamsi Sowerby, 1878, which was supposed to be deposited in the NHM, was found. Pictures of the name-bearing types are provided for further research on biodiversity of the island.     

Morphology and aestivation behaviour in some Madagascan acavid land snails

Nine species of Madagascan acavid land snails were compared in a phylogenetic context. The two most plesiomorphic, Clauator johnsoni and C. moreleti, differ from the others by their high-spired shells, short tentacles, short tails, long necks, and crawling mode of hitching the shell along the ground. In the seven more apomorphic species, the crawling mode is smooth, with the shell resting on the tail, and the relative lengths of tail and shell correlate significantly. Among these seven species, three pairs of closest relatives (Helicophanta petiti and H. uesicalis, H. farafanga and H. souuerbiana, Ampeltta decaryi and A. julii) show evidence of phylogenetic constraints on ranked shell size. Aestivation site (as tentatively inferred from rare data) does not correlate with shell shape or size: burrowers have H/D = 2.7 to 0.6 and D = 70 to 25 mm; arboreals have H/D = 0.8 to 0.5 and D = 70 to 30 mm; the species with both the highest spire and the smallest diameter (C. moreleti) is neither a burrower or an arboreal, but stays on the ground surface. Inferred aestivation sites are randomly distributed phylogenetically. Climate shows no correlation, except that the arborcals are only from humid to wet regimes. Uniform shell colouration occurs only in burrowers (C. johnsoni, H. petiti, H. uestcalis), but disruptive shell colouration occurs in all others, including burrowers (H. farafanga, A. decaryt), ground-surface aestivators (C. moreleti), arboreals (H. souuerbiana, A. julii), and semi-arboreals (Ampefita subfunebris). Among all nine species, burrowers have significantly thicker shells (than their close relatives of similar size), wider bodies, and longer snouts than non-burrowers (H. souuerbiana is exceptional in being arboreal despite its huge size and in having the broad foot and snout of a burrower). Thus, although there is some evidence for phylogenetic constraints, natural selection for aestivation and crawling behaviours seems to have dominated the evolution of external body morphology and of shell thickness (but not shell size and shape) in these snails.     

Cold tolerance in diapausing and non-diapausing stages of the flesh fly, Sarcophaga crassipalpis

ABSTRACT. Supercooling points (SCP) and low temperature tolerance were determined for larval, pupal and adult stages of Sarcophaga crassipalpis Macquart (Diptera: Sarcophagidae). No stage tolerates tissue-freezing. Ontogenetic changes in SCP profiles are similar for comparable developmental stages of diapause and non-diapause groups. Feeding larvae have SCPs near -7°C which decrease to -11°C in the postfeeding wandering phase of the final larval instar. The lowest SCPs are recorded for pupae at -23°C. The capacity to survive at -17°C varies with age of the diapausing pupae: 10-day-old pupae are less cold tolerant than pupae that have been in diapause for 45–80 days. Although the SCP of non-diapausing pupae is as low as in diapausing pupae, non-diapausing pupae are extremely sensitive to low temperature exposure and do not survive to adult eclosion when exposed to -17°C for as little as 20 min. The use of hexane to break pupal diapause has no effect on SCPs or low temperature tolerance.     

Characterization of 13 polymorphic microsatellite loci for two land snail species, Trochulus villosus and T. sericeus (Gastropoda: Pulmonata: Hygromiidae)

Thirteen new microsatellite loci were isolated and tested on two land snail species, Trochulus villosus and T. sericeus (Pulmonata: Hygromiidae), resulting in a set of eight polymorphic markers for each species. The expected heterozygosity was high for all loci and species (between 0.616 and 0.944). Such levels of variability will allow detailed insights into the population genetic structure of some Trochulus species.     

Ecology of freshwater snails in south-western Nigeria. I: Distribution and habitat preferences

Dry and rainy season investigations of diverse freshwater habitats in south-western Nigeria revealed fourteen species of snail comprised of nine pulmonates: Biomphalaria pfeifferi Krauss, Bulinus globosus Morelet, Bulinus rohlfsi Clessin, Lymnaea natalensis Krauss, Physa ( Aplexa) waterloti Germain, Bulinus forskali Ehrenberg, Gyraulus costulatus Krauss, Ferrissia sp, Segmentorbis sp. and five prosobranchs namely, Lanistes libycus Morelet, Lanistes ovum Peters, Pila wernei Philippi, Potadoma moerchi Reeve and Melanoides tuberculata Müller.The influence of diverse chemical and physical properties of water on their occurrence as well as interspecific and snail-plant relationships are discussed and maps showing the distribution of the species encountered are presented. Among the intermediate hosts of Schistosoma, B. globosus was widely distributed and common, B. pfeieri was also widely distributed but infrequent and B. rohlfsi was rare.     

Distribution of bulimulid land snails on the northern slope of Santa Cruz Island, Galapagos

The observations made along south-north transects on Santa Cruz Island's northern slope show that the distribution of bulimulid land snails follows a distinct zonation. Their zonation pattern is related to the well-marked plant zonation, the substrate and the important climatic gradient characterizing this area.
Live snails and shells belonging to 14 bulimulid taxa were collected along a transect (11 km long) starting from Cerro Puntudo, one of the island's highest points. Their distribution, the vegetal zonation and the rapid change in the climate observed along the transect are described.     

Functional aspects of shell geometry in some British land snails

Allometric relationships between the area of the shell mouth and live body weight are examined in 19 species of British land snails. Within species, the rate of increase of mouth area on weight is usually less than the isometric expectation, in spite of the logarithmic spiral pattern of growth in most species. It is suggested that this deviation is due mainly to changes in density with size. Two species which conform to isometric expectation alter the geometry of the shell as they pow.
Between species, the rate of increase in mouth area on weight in adults is much greater than isometric expectation, and the range of mouth areas at standard weight is considerable. These deviations are almost entirely accounted for by differences in shell geometry between large and small species, the former having higher rates of whorl expansion and smaller or non–existent umbilicuses.
The range of loading (weight per unit mouth area) on resting adult snails is thus much less than would be expected. It is suggested that large species are limited in the range of possible shell geometries by the need to minimize loading, while in small species other forces such as desiccation and predation may also be important: the range of geometries is generally larger. Observations on ecology and behaviour tend to support these conclusions.     

Biogeography of the Helicoidea (Mollusca: Gastropoda: Pulmonata): land snails with a Pangean distribution

The biogeography of helicoid land snails was investigated using cladistic methods. Parsimony analysis under Assumption 0 yielded twelve area cladograms (length=25, c.i.=0.76, r.i.=0.86). The pattern of vicariance for the Helicoidea indicated that families originated with the break up of eastern Gondwana and Laurasia between the late Mesozoic and mid-Tertiary, and possible vicariance events are identified. It is proposed that Asian terranes, located between India and Australia, maintained contact with northern Australia until the late Cretaceous, which is later than is suggested in current palaeogeographical hypotheses.     

High diversity and regional endemism in land snails of eastern Tanzania

In February/March 1995 we collected land snails (including slugs) at 12 stations in eastern Tanzania. A total of 571 person-hours yielded 9174 snails assigned to 159 morpho-species. The richest two sites each (<4ha of uniform forest) had 50 species (Amboni Cave) and 48 species (near Amani, Usambaras), nearly as great as the most species-rich sites known in the world; sieving of litter and soil would probably yield more species. In lowland (coastal) forests, both diversity and endemism seemed to decrease from north to south. Most snail species were found within only one of four coastal or one montane geographic regions, indicating substantial regional endemism. Only one species (Achatina fulica) appeared in all five regions, and 84% of all other species were found in only one (61%) or two regions (23%). The predatory streptaxids comprised about half the species and a third of the individuals at the Usambara site, an extremely high ratio of carnivores. Small snails (< 5mm greatest adult shell dimension) – many of which are probably undescribed species – comprise a substantial proportion of Tanzanian molluscan diversity; more surveys are needed, especially because of human pressures on the few forest patches remaining.     

Ecological and morphological diversification within single species and character displacement in Mandarina,endemic land snails of the Bonin Islands

The endemic land snail species Mandarina hahajimana has undergone extensive habitat and morphological diversification within the Hahajima islands in the Bonin archipelago. This species has diversified into populations with ground, arboreal and semi-arboreal life histories. In addition, arboreal populations and semi-arboreal populations show diversification in preferences of species and positions of the tree on which they are found. Shell morphologies of M. hahajimana exhibit remarkable geographical variation, and they have a clear relationship with their life histories. The morphological variation of M. hahajimana results from adaptation to different lifestyles. The habitats of these populations influence the relationships with other species of Mandarina coexisting with M. hahajimana. This suggests that the morphological and ecological divergence within M. hahajimana has been induced by competitive interaction with other species of Mandarina. Character displacement may have played an important role in promoting adaptive radiation of Mandarina in the Bonin Islands.     

The biogeography of land snails in the islands of the Gulf of Guinea

Data on land snail diversity in the Gulf of Guinea islands is presented and the biogeography of the Gulf of Guinea fauna is discussed with reference to island snail faunas in the other areas of the world. Although the land snail faunas of the four islands clearly have west and central African affinities, speciation events following rare colonizations have led to high rates of endemism at the species and generic levels. The influence of island size, altitude, isolation and other factors on the development of the land snail faunas is discussed. The effect of land use changes on the land snail fauna over the last 150 years is evaluated. Current threats include recent changes in agricultural practice leading to the destruction of snail habitats in both forest and plantation areas. The potential threat posed by introduced species is also discussed. The Gulf of Guinea snail faunas appear to be in relatively good health in comparison to many other island snail faunas. However, the uniqueness of the faunas makes it imperative that further ecological and taxonomic research is undertaken both to understand the processes by which they developed and to evaluate the current status of many species in terms of distribution and threats.     

Variation in foot size and shape in some British land snails and its functional significance

Live weight, and the length, breadth and surface area of the extended foot sole were measured in 24 species of British terrestrial snails. Allometric relationships between these variables are described, concentrating on the relationship between foot surface area and weight. Intraspecific foot area/weight relationships deviate from isometric expectation for several species; this may be attributed to density changes, foot-shape variation or the physical constraint imposed by shell aperture size.
The rate of increase of foot sole area with live weight among species is greater than expected under isometry, indicating that larger species partially compensate for the increase in foot loading (weight per unit foot area). The rate of whorl expansion of the shell is related to the deviations from the interspecific foot area/weight relationship, reinforcing the possibility that shell aperture area may limit foot size in some species. Foot ratio (foot length:foot width) is negatively related to live weight and foot loading.
The findings are discussed in relation to the known behaviour and microdistribution patterns of the species.     

Influence of shell colour on the mortality rate of the land snail Arianta arbustorum under different microclimatic regimes

The mortality of phenotypic shell colour morphs and age classes of the snail Arianta arbustorum in several microclimatic conditions was recorded. An analysis of variance was performed on five factors: adaptation temperature, relative humidity, shell colour, age class and test temperature. There were no significant differences in the mortality between different adaptation temperatures or relative humidities, but the interaction of these two factors was highly significant. There were significant differences in mortality rate between test temperature and age class. The mortality of the brown morph was higher than the yellow one at all adaptation temperatures (overall, P < 0.05). There were no significant differences between the mortality rates of the two morphs at different relative humidities. The mortality of the brown morph was higher than that of the yellow at six out of seven test temperatures. Juvenile snails survived significantly better than adults at all test temperatures.     

Degradation of the radula in the snails Biomphalaria glabrata say and Limnaea stagnalis L. (Gastropoda,Pulmonata)

Summary The radula of snails is formed at the posterior end of the radular gland or pocket, and degraded at the same rate at its anterior end. Degradation is due to different secretory activities of the inferior epithelium of the radular gland. Its secretions seem to degrade enzymatically the matrix of the radular membrane and basal plates of teeth, leaving only chitin containing microfibres and degradation products. The sclerotized parts of the teeth remain unchanged, but as they are now only loosely connected with the radular membrane. they are torn off easily during feeding movements. The rest of the degraded and frayed radular membrane and the subradular membrane are also lost by abrasion during feeding. The cells of the inferior epithelium are connected with each other by septate desmosomes and an elaborate system of deep lateral interdigitation which may provide tensile strength. Extrusion of degraded cells of the inferior epithelium into the subradular membrane takes place, although the thick basal lamina forms a continuous sheath which is closely adjoined to the basal parts of the inferior epithelium. Nerve fibres containing vesicles with electron dense neurosecretory material (deduced from the diameter of 200–250 nm) are attached to this sheath or penetrate into it; they may be involved in the regulation of production and degradation processes during radula replacement. Problems of the forward transport of radula and inferior epithelium are discussed.     

论滩地灭螺林的概念与应用

根据“兴林灭螺”产生背景,发展现状和重要影响,阐述滩地灭螺林与其他林种之间的区别,滩地灭螺林除具有灭螺防病的功能之外,还有其特殊的地理环境,特定的树咎构成,特异的营造技术和林相结构;总结滩地灭螺林的经营原则是超强度集约经营,短周期经营,规模经营和综合经营,因此滩地灭螺林在林业生产中应划分为一个新的林种,提出长江中下游沿江地区新的林种结构是滩地灭螺林、防护林,经济林与景观游憩林,并就如何加快发展滩地     

The influence of the ecological characteristics of phytocoenoses on the percentage proportions of zoogeographical elements in the malacocoenoses of land snails (Mollusca: Gastropoda terrestria)

The influence of 11 forest phytocoenoses in a single area (the Medvednica Mountain in north-western Croatia) on the composition of the zoogeographical elements of the land malacofauna was analysed. It was established that malacocoenoses in different plant associations of the same phytogeographical and zoogeographical area have different compositions in respect to the zoogeographical elements of the land snail fauna. Zoogeographical elements located on borders of the range display the widest divergences in their percentage representation in the malacocoenoses of the forest phytocoenoses of a single area. This is due to varying ecological conditions in the phytocoenoses under investigation.Abbreviations as. = association - subas.= subassociation     

Australian land snails: a review of ecological research and conservation approaches

Land snails are an important yet often neglected component of Australia's biological diversity. Despite high levels of diversity within this group and the identification of many narrow range endemic species as being of conservation concern, there have been few detailed studies that document the ecology and conservation requirements of the group. A range of threats has been suggested, yet relatively few have been rigorously assessed. Whilst factors such as land clearing are readily apparent and have resulted in extinctions, other threats such as climate change are not well understood. This paper reviews studies conducted on terrestrial molluscs in Australia and highlights the need for further targeted ecological research, given the likely level of on-going threats. We urge researchers to apply rigorous approaches to data collection that will enable a deeper understanding of the factors governing distribution and abundance. Approaches used in other areas of conservation biology offer considerable scope for application to land snails and for the development of appropriate conservation strategies.