POPULATION STRUCTURE AND LEVELS OF GENE FLOW IN THE MEDITERRANEAN LAND SNAIL ALBINARIA CORRUGATA (PULMONATA: CLAUSILIIDAE)

The amount of gene flow among local populations partly determines the relative importance of genetic drift and natural selection in the differentiation of such populations. Land snails, because of their limited powers for dispersal, may be particularly likely to show such differentiation. In this study, we directly estimate gene flow in Albinaria corrugata, a sedentary, rock-dwelling gastropod from Crete, by mark-recapture studies. In the same area, 23 samples were taken and studied electrophoretically for six polymorphic enzyme loci. The field studies indicate that the population structure corresponds closely to the stepping-stone model: demes are present on limestone boulders that are a few meters apart, and dispersal takes place mainly between adjacent demes. Average deme size (N) is estimated at 29 breeding individuals and the proportion of migrants per generation at 0.195 (Nm = 5.7). We find no reason to assume long-distance dispersal, apart from dispersal along occasional stretches of suitable habitat. Genetic subdivision of the population, as derived from F_ST values, corresponds to the direct estimate only at the lowest spatial level (distance between sample sites < 10 m), where values for Nm of 5.4 and 17.6 were obtained. In contrast, at the larger spatial scales, F_ST values give gene-flow estimates that are incompatible with the expected amount of gene flow at these scales. We explain these discrepancies by arguing that gene flow is in fact extremely limited, making correct estimates of Nm from F_ST impossible at the larger spatial scales. In view of these low levels of gene flow, it is concluded that both genetic drift and natural selection may play important roles in the genetic differentiation of this species, even at the lowest spatial scales.     

NATURAL HISTORY AND POPULATION DYNAMICS OF THE LAND SNAIL HELIX TEXTA IN ISRAEL (PULMONATA: HELICIDAE)

Helix texta is endemic to the Mediterranean regions of Israel.It has a seasonal activity pattern which starts in the autumn,with the first rains, and dwindles towards the spring, whenthe snails dig into the ground for a six months long aestivation.A cold spell of 0°C will, however, terminate the activeseason of the adult snail, even in the middle of the rainy season.Survival of the young is very low and most of them (90%) donot survive their first year, because of the winter cold andthe summer drought. Massive predation of adult snails by wild boar was observedin December 1986: within a few days, about 50% of the adultsin the study in the area were eaten. A very rapid growth ofyoung and subadults was observed immediately after this predation.These observations suggest that the extent of recruitment ofnew adults to the population may be partly controlled by existingadults, through a growth-inhibiting pheromone in the mucus.After predation this inhibiting factor disappears, enablinga subsequent rapid growth of the young. In this manner, massive,irregular predation of the adults by a large predator, and changesin juvenile survival, result in sharp fluctuations in the agestructure of the population. The resulting pattern of unstablepopulation dynamics is different from that described for theEuropean species of Helix. (Received 16 January 1989; accepted 17 April 1989)     

贵州洞穴陆生贝类一新种(肺螺亚纲,柄眼目,烟管螺科)

记述了贵州省洞穴烟管螺科真管螺属1新种,即荔波真管螺Euphaedusa libonensis sp.nov．,标本采自贵州省荔波县董背洞内。对新种进行了详细描述,并与近似种做了比较。模式标本保存在中国科学院动物研究所无脊椎动物标本馆。     

MITOCHONDRIAL DNA AND MORPHOLOGICAL DIFFERENTIATION OF ALBINARIA POPULATIONS (GASTROPODA: CLAUSILIIDAE)

Albinaria, despite its restricted geographical distribution,exhibits an extreme degree of differentiation. The use of conventionalor numerical taxonomy has not facilitated the understandingof evolution of the genus. Twelve populations belonging to fourspecies were studied with a combined approach using mitochondrialDNA (mtDNA) and qualitative morphological data. The completemtDNA genome of A. coerulea from Amorgos island was cloned andused in mtDNA restriction site analysis of the other populations.Maximum parsimony cladistic analysis of nine populations providedtrees sharing the same basic topology. Certain restriction sitesand morphological characters appear to be species specific,while incongruity is observed at the intraspecific level. Sequencedivergence and the paleogeographic history of the area wereused for construction of an evolutionary scenario and a roughestimation of the Albinaria mtDNA clock. (Received 7 February 1994; accepted 20 July 1994)     

MITOCHONDRIAL PHYLOGEOGRAPHY OF THE LAND SNAIL ALBINARIA IN CRETE: LONG-TERM GEOLOGICAL AND SHORT-TERM VICARIANCE EFFECTS

The land snail genus Albinaria exhibits an extreme degree of morphological differentiation in Greece, especially in the island of Crete. Twenty-six representatives of 17 nominal species and a suspected hybrid were examined by sequence analysis of a PCR-amplified mitochondrial DNA fragment of the large rRNA subunit gene. Maximum parsimony and neighbor-joining phylogenetic analyses demonstrate a complex pattern of speciation and differentiation and suggest that Albinaria species from Crete belong to at least three distinct monophyletic groups, which, however, are not monophyletic with reference to the genus as a whole. There is considerable variation of genetic distance within and among “species” and groups. The revealed phylogenetic relations do not correlate well with current taxonomy, but exhibit biogeographical coherence. Certain small- and large-scale vicariance events can be traced, although dispersal and parapatric speciation may also be present. Our analysis suggests that there was an early and rapid differentiation of Albinaria groups across the whole of the range followed by local speciation events within confined geographical areas.     

FOOD SELECTION IN THE LAND SNAIL LIMICOLARIA FLAMMEA MULLER (PULMONATA: ACHATINIDAE)

Food consumption by juvenile and adult specimens Limicolariaflammea was measured as dry weight of food eaten. The snailwas fed weekly for 15 months on four types of food (lettuce,potato, apple and carrot) and chalk provided, hence an opportunityto select for food. Juvenile snails showed greater selectivitydepending on whether the food was needed for somatic growthor reproduction. On the other hand, when fed exclusively onone each of the same food items and given no opportunity tochoose, the snails grew better on the same food items they selectedin the choice experiment. The absorption efficiencies (AD) werehigh, the utilisation efficiency (ECI) was 1–13% and showeddistinct peaks corresponding to egg production. Values for ECDwere 1.25–15.5%. Variation in growth rates was due mainlyto utilisation efficiencies of the four foods tested. Largeamounts of chalk were eaten during the period of somatic growthand greatly reduced during the reproductive phase of L. flammea.The significance of these findings to the snails ecology isdiscussed. (Received 9 April 1991; accepted 11 June 1991)     

CONSUMPTION OF AMPHIPODS BY THE NEW ZEALAND LAND SNAIL WAINUIA URNULA (PULMONATA: RHYTIDIDAE)

An unusual carnivorous diet was documented for the rhytididsnail Wainuia urnula urnula (Pfeiffer) from the southern North Island,New Zealand. Eighty-two percent of 315 samples of faeces or gutcontents contained remains of landhoppers (Crustacea: Amphipoda).Earthworms (Oligochaeta) were the second most common food typeidentified, but occurred in only 4 percent of samples. In the laboratory,W. urnula urnula captured landhoppers by rapidly everting theTVU-section odontophore beneath the prey and immediately drawingit into the mouth in a single action. Diet samples from the allopatriccongeners W. edwardi (Suter) (n 5 51) and W. clarki Powell (n5 7) contained no remains of landhoppers, and these snails didnot eat landhoppers in the laboratory. The diet of these specieswas dominated by earthworms. The subspecies W. u. nasuta ateboth earthworms and amphipods with similar frequency (n 5 40).Individual teeth on the radula of W. urnula urnula had a simpleblade-like cusp like other Wainuia species, but there were fewerteeth per row and fewer rows on the whole radula than in otherspecies. W. u. nasuta had a similar number of rows of teethto W. clarki and W. edwardi, but the number of teeth per rowwas intermediate between these species and W. u. urnula. Recordsof pulmonate species preying on arthropods are rare, yet inthe case of W. urnula this specialization has been accompaniedby minimal morphological change. (Received 22 December 1998; accepted 11 March 1999)     

中国陆生贝类一新种(肺螺亚纲:柄眼目:拟阿勇蛞蝓科)

作者于1981～1983年,参加中国科学院横断山综合考察队,赴云南地区进行考察,又于1993～1994年,赴滇南一带调查,获得陆生贝类标本一批,经整理鉴定,得拟阿勇蛤蝓科一新种：即云龙隐带螺Cryptozonayunlongensissp.nov.。本文对新种的形态特征作了详细描述,并对生殖系统进行了解剖,对颚片和齿舌作了电子显微镜观察,与其近似种古怪隐带螺Cryptozonaerratica（Heude,1882）进行了比较。     

THE INFLUENCE OF INGESTIVE CONDITIONING ON FOOD CHOICES IN THE LAND SNAIL HELIX ASPERSAMULLER (GASTROPODA: PULMONATA: STYLOMMATOPHORA)

An experiment of food choice in one-day-old naïve landsnail Helix aspersa Müller was carried out, involving threephases. First, a training period on a monophagous diet of leafdiscs of Taraxacum officinale or Urtica dioica was given for1, 5, 10, 15 or 30 days. The area of leaf discs consumed byeach snail during this stage was assessed. In the intermediatephase, the animals were not fed for 24hours. Finally, food choicewas tested over 24 hours, when animals could eat leaf discsof each species of plant usedfor training. A coefficient offood preference for Urtica dioica was calculated (UPC = areaof Vrtica leaf disc consumed/area of Urtica and Taraxacum discsof leaves consumed for 24 hours). The length of the training phase did not reduce the percentageof individuals preferring the plant previously consumed. Onthe contrary, after 15 days of monophagous diet, animals formerlyfed on Urtica showed a coefficient of food preference for Urticasignificantly higher than Taraxacum fed animals, and after 30days of training this phenomenon was more pronounced. Thus,during the choice test, snails ate more of the previously eatenplant leaf. Our experiment highlighted the feeding behaviourplasticity of H. aspersa. The significant correlation betweenthe area of Urtica eaten during the training phase and the coefficientof food preference for Urtica is discussed. (Received 10 April 1994; accepted 10 January 1995)     

中国管螺属三新种（肺螺亚纲：柄眼目：烟管螺科）

本文记述烟管螺科、管螺亚科、管螺属三新种：雅安管螺、阳朔管螺和德宝管螺。前一种采自四川省雅安,后两种分别采自广西僮族自治区阳朔县和德宝县境内。     

GROWTH, SURVIVORSHIP, AND POPULATION SIZE IN THE LAND SNAIL RHAGADA CONVICTA COX, 1870 (PULMONATA: CAMAENIDAE) FROM A SEMIARID ENVIRONMENT IN WESTERN AUSTRALIA

Basic characteristics of a population of the camaenid land snailRhagada convicta were studied in a semiarid environment nearNorth West Cape, in Western Australia. Consistent evidence frommark-recapture studies and analysis of size-frequency distributionindicates an average annual increase in shell diameter of 3.6mm, with an average period of 5 years from hatching to reachadult size. These rates are low, compared with most other landsnails studied, including cama-enids from wetter environments.Estimates of mortality rate and the rate of recruitment intothe adult population indicate that the snails live an averageof approximately 5 years after reaching adult size, which meansthat the period of turnover for this population is approximately10 years. The population density was estimated to be 0.8 adultsper m², with a total population size (± s.e.) of 875± 164. The population is very localised, with an estimateddiameter of the neighbourhood area of only 38 m. (Received 28 August 1990; accepted 12 February 1991)     

THE EFFECT OF COLLECTIVE DISPERSAL ON THE GENETIC STRUCTURE OF A SUBDIVIDED POPULATION

Correlated dispersal paths between two or more individuals are widespread across many taxa. The population genetic implications of this collective dispersal have received relatively little attention. Here we develop two‐sample coalescent theory that incorporates collective dispersal in a finite island model to predict expected coalescence times, genetic diversities, and F‐statistics. We show that collective dispersal reduces mixing in the system, which decreases expected coalescence times and increases F_ST. The effects are strongest in systems with high migration rates. Collective dispersal breaks the invariance of within‐deme coalescence times to migration rate, whatever the deme size. It can also cause F_ST to increase with migration rate because the ratio of within‐ to between‐deme coalescence times can decrease as migration rate approaches unity. This effect is most biologically relevant when deme size is small. We find qualitatively similar results for diploid and gametic dispersal. We also demonstrate with simulations and analytical theory the strong similarity between the effects of collective dispersal and anisotropic dispersal. These findings have implications for our understanding of the balance between drift–migration–mutation in models of neutral evolution. This has applied consequences for the interpretation of genetic structure (e.g., chaotic genetic patchiness) and estimation of migration rates from genetic data.     

THE LIFE CYCLE, POPULATION DYNAMICS, GROWTH AND SECONDARY PRODUCTION OF THE SNAIL BRADYBAENA FRUTICUM (MULLER, 1774) (GASTROPODA PULMONATA) IN NORTHERN GREECE

The life cycle, population dynamics, growth and secondary productionof the pulmonate land snail Bradybaena fruticum were studiedin northern Greece. The demographic analysis of the populationsof B. fruticum revealed that a) two cohorts exist in the fieldthroughout the year b) the reproductive period started in thebeginning of summer and c) growth was increased during springand autumn. According to von Bertallanffy' method B. fruticum needs 5 yearsto attain its maximum size in the field of 25.40 mm. Mortalityrate increases and life expectancy decreases with increasingage. Net reproductive rate (Ro) was equal to 3. 15 and per capitarate of increase (r^c) was equal to 1. Annual secondary production, calculated by Hynes' size frequencymethod, revealed a mean annual density of 5.9 individuals/m²,a mean standing crop (B) of 8.09 g/m²/year and an annual production(P) of 1.92 ± 0.11g/m²/year. Annual turnover ratio (P/B)was equal to 2.37. (Received 25 May 1989; accepted 17 March 1989)     

DISPERSAL PATTERNS OF THE GIANT AFRICAN SNAIL, ACHATINA FULICA (FERUSSAC) (STYLOMMATOPHORA: ACHATINIDAE), EQUIPPED WITH A RADIO-TRANSMITTER

The dispersal pattern of the African giant snail, Achatina fulica(Férussac) was examined by radio-tracking for six months.They showed typically nocturnal locomotory activities. Theiractivities differed among three developmental stages; juvenile,young adult, and old adult. Juveniles dispersed for the longestdistances. The most active juvenile moved 500 m in 6 months.Young adults and old adults travelled only within a narrow area,although the dispersal range for young adults was greater thanthat of old adults. (Received 15 September 1992; accepted 11 December 1992)     

GROWTH AND REPRODUCTION OF THE MINUTE LAND SNAIL PUNCTUM PYGMAEUM (DRAPARNAUD)

Reproductive characters and growth of Punctum pygmaeum wereinvestigated under laboratory conditions. Eggs were laid singlyat intervals of 2–8 days. Egg size averaged 0.41 by 0.50mm. Due to a variable period of egg retention, newly depositedeggs contained differently developed embryos resulting in anincubation period varying from 1 to 34 days. Each snail on averagelaid 6.0 eggs (range 1–16 eggs) during its life. Egg productionrate and hatching success in individuals kept in isolation werethe same as in individuals kept in pairs. Hatchlings measured0.49 mm in shell breadth. Snails grew throughout their life,but the growth rate declined significantly at a shell breadthof 1.3–1.4 mm, the point at which the onset of sexualmaturity occurred. Comparison of reproductive characters ofsnails living in leaf litter revealed that very small-sizedspecies produce few, but in relation to their shell size largeeggs, which they oviposit singly. ^*Present address: Zoological Institute, University of Basel,Rhein-sprung 9. CH-4051 Basel, Switzertand (Received 23 May 1988; accepted 11 July 1988)