Metabolism of cholecalciferol in land snails.

1. Radioactively labelled cholecalciferol was injected into the land snails Levantina hiersolyma and Theba pisana. Three metabolites (C, D and E), more polar than cholecalciferol, were found. 2. Metabolite C was found to be identical with 25-hydroxycholecalciferol. On injection of 25-hydroxy[26,27-3H]cholecalciferol, metabolite E was predominantly formed. Metabolite D was predominantly formed from cholecalciferol. Metabolites D and E differ from any known cholecalciferol metabolites. 3. The intestine was found to be the tissue capable of carrying out the transformation of 25-hydroxycholecalciferol into metabolite E. 4. 25-Hydroxycholecalciferol and metabolite E were localized in the digestive gland of the snail, the tissue responsible for the absorption of Ca2+ and its storage. Metabolite D was not localized in any specific tissue.     

Cold-hardiness in several species of land snails

1. 1.|Mean supercooling points (SCP) of Anguispira alternata (Say) gradually declined in autumn and increased in spring. SCP also declined in autumn in Discus conrkhitei (Newcomb) and Gastrocopta armifera (Say).

2. 2.|Supercooling ability varied among the species, being the greatest in G. armifera.

3. 3.|Prolonged exposure of winter animals to high temperatures resulted in only a modest increase in SCP.

4. 4.|Low temperature survival of D. cronkhitei and G. armifera was slightly poorer than predicted by the mean SCP.

Parallel evolution in Marquesan partulid land snails

Partulid land snails of the genus Samoana inhabiting the Marquesas Islands of French Polynesia exist as two distinct types, the 'thick-shelled' and 'thin-shelled' species. The two types differ in size, shell-thickness, pigmentation of the shell and mantle, stickiness of the mucus, and length of the tentacles. A study of variation in allozymes indicates that the species form a monophyletic group, within which the differences between the two types have twice evolved independendy, once in the northern islands and at least once in the south. In the Society Islands the two suites of characters are found in both Partula and Samoana , where there is evidence of at least four other independent derivations of the two types. The thin-shelled species consistendy tend to occur at the higher altitudes (above 200 m). These cases of parallel evolution argue strongly that the complexes of associated characters have arisen through natural selection.     

Geographic and ecological patterns in Turkish land snails

The distribution of Turkish land snails has been examined, using data from a monograph by H. Schütt (1993). Turkey has been divided into eight regions for purposes of describing localization of fauna. On average, species occupy 1.7 regions. About 36% of the fauna is known from Turkey alone. There are affinities with Europe, the Caucasus, the eastern Mediterranean and the Levant and Middle East. The influence of neighbouring faunas shows up when the similarities of the eight regions are clustered. As usual, the fauna contains a high spired and a discoidal mode of shell shape, with species covering a wide range of sizes. Clausiliacea occupy a higher mode than other high spired species, while Helicacea become progressively more equidimensional from small to large species. The pattern of shell size and shape varies between regions, smaller and high spired species being most common in cooler and damper parts, larger discoidal species in parts with Mediterranean or continental dry climates. A test for evidence that animals of the same shape and size are more likely to be allopatric than sympatric failed to show that they were. The fauna is dominated by a few families to a greater extent than that of Europe, and is more like that of the isolated Madeiran archipelago. It is suggested that the Turkish fauna still shows evidence of external penetration with some local radiation, in the manner of the oceanic islands, and has not evolved to become a balanced assemblage such as is seen in Europe.     

Biogeographical tests of the vicariance model in Mediterranean land snails

Aim To investigate the importance of vicariance in shaping land snail faunas. Location Three data sets of Mediterranean land snails were analysed: Helicoidea of the Iberian Peninsula and the complete land snail faunas of the central and eastern Aegean Islands and of Israel and Palestine. Methods The vicariance model predicts a clustering of species ranges. We tested for clustering of species ranges with a Monte Carlo simulation. For this simulation we used a null model that generates range data sets in such a way that their range size distribution, their species richness distribution and the spatial autocorrelation of the ranges approximate the parameters in the real data set. Biotic elements (clusters of species ranges) were delimited with model‐based Gaussian clustering. A second prediction of the vicariance model is that closely related species belong to different biotic elements. This was tested with a chi‐squared test. Results The distribution areas of the Iberian Helicoidea and the Israeli/Palestinian land snails are significantly clustered. The same is true for Israeli/Palestinian land snail species belonging to groups with geographically restricted species. However, the clustering is not significant in the complete central and eastern Aegean land snail data set, the Iberian Helicoidea species, and the central and eastern Aegean land snails belonging to groups with geographically restricted species. Contrary to the prediction of the vicariance model, closely related Iberian Helicoidea species and Israeli/Palestinian land snails belong significantly more often to the same biotic element than expected by chance. The null hypothesis that closely related species are homogeneously distributed across biotic elements cannot be rejected only for the data set that includes the Israeli/Palestinian land snails belonging to groups with geographically restricted species. Main conclusions The patterns found in the central and eastern Aegean land snail and the Iberian Helicoidea data sets do not correspond with the predictions of the vicariance model. This indicates that speciation modes other than vicariance were frequent, or that the distribution areas of many species in these faunas were largely modified by extensive post‐speciation dispersal and/or regional extinction. Hardly any possible vicariance events that might have contributed to the origin of the observed biotic elements in the Israeli/Palestinian land snail fauna could be identified. On the contrary, the biotic elements of the Israeli/Palestinian land snail fauna correspond with ecological factors. Vicariance has had only a limited influence on current biogeographical patterns in Mediterranean land snails.     

Inverse temperature acclimation of heart rate in hibernating land snails

Summary The heart rates of quiescent land snailsHelix lucorum andH. aspersa were recorded by impedance pneumography over several days. When snails acclimated to warm, humid, long days were transferred in late autumn to cool, dry, short days, in order to permit hibernation inverse rotational acclimation occurred, so that heart rates at low temperatures were lowered. However, temperature dependence increased so that heart rates at higher temperatures showed less difference. When hibernatingH. lucorum were brought into warm conditions and allowed to emerge from hibernation, their heart rates at low temperatures were raised. WarmacclimatedH. lucorum showed lower rates and higher temperature dependence before hibernation than after emergence: this may assist their entry into hibernation.H. lucorum showed a higher temperature dependence thanH. aspersa whether warm- or cold-acclimated: this may reflect the lower summer temperatures experienced by this population ofH. lucorum and the obligate nature of their winter dormancy.     

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.     

Spire index and preferred surface orientation in some land snails

Fourteen species of land snails have been tested for their preference for surfaces at 0, 90 or 180 degrees under laboratory conditions. They range from high-spired (height/breadth = 4.1) to discoidal forms (height/breadth = 0.4). There is a positive association of spire height with tendency to adopt the 90 degree surface. Species of intermediate (globular) shape show less specificity for a particular surface than high- or low-spired species. The exception is Helix aspersa , which behaves more like one of the high-spired species than like one of its similarly shaped relatives. The differences in preference will help to reduce interaction between co-existing species in the field.     

Species richness in Madeiran land snails, and its causes

Aim  To unravel the reasons why a group of islands of 800 km² area should support over 200 extant land snail species.
Location  The temperate Atlantic Madeiran archipelago.
Methods  Distributional surveys and model testing.
Results  Repeated volcanic events have changed the topography of the islands and created periodic further isolates. There has been climatic fluctuation and varying sea level. Individual locations are not species-rich, but there is replacement from one subregion to another. Evidence of competitive interactions is lacking.
Main conclusions  High diversity results from the fortuitous coincidence of rates of geological and climatic change and isolation on the one hand, and migration and genetic divergence on the other. Hubbell's neutral model of biodiversity explains species richness if a factor is added describing structural instability or periodicity, here called the geodetic rate. This geodetic, biological interaction can explain why some archipelagos are species-rich.     

Simultaneous character convergence and divergence in Western Australian land snails

Three distantly related genera of land snails, Amplirhagada Iredale, 1933, Quistrachia Iredale, 1939, and Westraltrachia Iredale, 1933, overlap in distributions only in the Napier and Oscar Ranges, east of Derby, Western Australia. The first two remain allopatric, Quistrachia having a more eastern range, while Westraltrachia overlaps both ranges. In the zone of sympatry, with changes proceeding from east to west, Westraltrachia diverges in feeding, and there is massive, gradual convergence in shell size, shape and colour between Amplirhagada and Westraltrachia. Shells of both genera depart markedly from their distinctive allopatric appearances to form a new morphotype in the north-west Napier Ranges. The species there are so similar in appearance that the two genera cannot be identified at a distance of 0.5 m. Thirteen species-level taxa are involved in these changes, four allopatric Amplirhagada , seven allopatric Westraltrachia, Quistrachia monogramma and Rhagada basedowana.
Westraltrachia species, the only large land snails in their main area of distribution (south-east Kimberlcy), are pre-adapted to graze on an occasionally present food resource, algal-fungal blooms on limestone seepage faces. They entered the Oscar and Napier Ranges, where this food resource is more abundant, and large land snails that are generalized feeders, Amplirhagada or Quistrachia , were already present and abundant. Hence feeding divergence occurred. Such specialization by Westraltrachia to minimize competition is readily understandable.
The selective pressures that led to the striking convergence in shell features in north-west Napier taxa are unknown.     

Resistance to desiccation and distribution patterns in bush-dwelling land snails

Bush-dwelling land snails are exposed to desiccating conditions that are more severe than those of snails that seek the shelter of rock crevices, litter or the upper layers of the soil. We studied the resistance to desiccation in four bush-dwelling species of Israeli snails to evaluate a possible relation between their water economy and their distribution pattern. The resistance to desiccation decreased in the following order: Xeropicta vestalis (a widely distributed Mediterranean species), Trochoidea simulata (a desert species), Theba pisana (a Mediterranean species from the sand dunes of the coastal plain), and Monacha haifaensis (a Mediterranean species). Xeropicta vestalis also had the quickest response to the desiccating conditions. It is probably prevented from establishing itself in the desert, in spite of its superior water economy, because it is an annual, semelparous species, and the desert is a highly unpredictable environment. An immediate response to desiccating conditions may be a key factor in the success of desert-inhabiting land snails. Snails from more humid regions take several days to recruit their water preserving mechanisms, a delay which may be crucial to their water balance. The conchiometrics of X. vestalis and T. simulata suggest that the main water preserving mechanisms of these species are located in the mantle, rather than in the shell and epiphragm.     

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.     

Hemagglutinins in brown seaweeds

Twenty-eight brown seaweeds contain agglutinins that show activity against animal and human erythrocytes. Three brown seaweeds are described whose hemagglutinic activity has not been previously reported: Ectocarpus confervoides, Giffordia granulosa and Cutleria multifida. Hemagglutinic activity against different erythrocytes is as follows: rabbit, 100%; sheep, 71%; chicken, 64%; guinea-pig, 39%; human, 38%; horse, 25% and calf, 21%. The highest agglutinic activity was found with rabbit erythrocytes, with maximum titres of: Fucus serratus (2¹⁸), Laminaria saccharina (2¹⁷) and Himanthalia elongata (2¹⁷). The species Giffordia granulosa showed certain specificity against human erythrocytes. In general, the hemagglutinic activity of these brown seaweeds seems to be of a polyphenolic nature. Agglutinic activity of some of these brown seaweeds can be used as a taxonomic index.     

Bronze Age shipwreck snails from Turkey: first direct evidence for oversea carriage of land snails in antiquity

Thirty-six shells of terrestrial gastropods were discoveredin underwater archaeological excavations of a Late Bronze Age(3,300 years BP) shipwreck at Uluburun, southern Turkey. Fourshells were not related to the wreck and belonged to local speciesfrom the nearby coast. The other 32 specimens were accidentallytransported with the merchant ship, which had sunk when sailingin a counterclockwise route from the Syro-Palestinian coastvia Cyprus to the Aegean and then to Egypt. The Near Easternendemic Xerocrassa langloisiana and the common eastern Mediterraneansynanthrope Xeropicta krynickii were found in amphoras originallycontaining terebinth resin, destined for Egypt. The combinedranges of the two species and the morphological record pointto a narrow area near the Dead Sea, more than 50 km distantfrom the Mediterranean coast, as the harvesting locality ofthe resin. A second group of land snails, partly determinedas Xp. krynickii, must have been on board the vessel under differentcircumstances, attached to spiny bushes used to cushion theheavy freight and to prevent the planks from being damaged.The finds provide direct evidence that land snails have beencarried on ships for more than 3,000 years, and underline assumptionsthat human-based oversea dispersal of anthropochorous speciesin the Mediterranean has occurred since antiquity. The resultsalso show how much can be done if we possess a detailed faunisticknowledge of species distributions and shell morphology. (Received 11 September 2007; accepted 6 November 2007)     

Heat shock proteins and resistance to desiccation in congeneric land snails

Land snails are subject to daily and seasonal variations in temperature and in water availability and depend on a range of behavioral and physiological adaptations for coping with problems of maintaining water, ionic, and thermal balance. Heat shock proteins (HSPs) are a multigene family of proteins whose expression is induced by a variety of stress agents. We used experimental desiccation to test whether adaptation to different habitats affects HSP expression in two closely related Sphincterochila snail species, a desiccation-resistant, desert species Sphincterochila zonata, and a Mediterranean-type, desiccation-sensitive species Sphincterochila cariosa. We examined the HSP response in the foot, hepatopancreas, and kidney tissues of snails exposed to normothermic desiccation. Our findings show variations in the HSP response in both timing and magnitude between the two species. The levels of endogenous Hsp72 in S. cariosa were higher in all the examined tissues, and the induction of Hsp72, Hsp74, and Hsp90 developed earlier than in S. zonata. In contrary, the induction of sHSPs (Hsp25 and Hsp30) was more pronounced in S. zonata compared to S. cariosa. Our results suggest that land snails use HSPs as part of their survival strategy during desiccation and as important components of the aestivation mechanism in the transition from activity to dormancy. Our study underscores the distinct strategy of HSP expression in response to desiccation, namely the delayed induction of Hsp70 and Hsp90 together with enhanced induction of sHSPs in the desert-dwelling species, and suggests that evolution in harsh environments will result in selection for reduced Hsp70 expression.     

Supergenes in polymorphic land snails. II. Partula suturalis.

The colour and banding of the shell of Partula suturalis are controlled by a single locus (M) with a series of at least six alleles. MX, giving apex as a homozygote, is dominant to MF1, giving frenata, which is dominant to the other alleles. MF2 is similar to MF1 except in its relation with MA. MF2MA produces bisecta and provides a striking example of a heterozygote that is qualitatively different from both homozygotes for the alleles producing it. MA gives atra as a homozygote and is dominant to MC and MS. MC, giving cestata as a homozygote, is recessive to all except MS. MS, giving strigata, is the universal recessive. It is suggested that the locus may be complex. The direction of coiling of the shell is determined by the H locus with HS (sinistrality) dominant to HD (dextrality). The expression of coiling is delayed by one generation, the maternal genotype determining the phenotype of the offspring. M and H are not linked. Self-fertilisation occurs infrequently and non-randomly.