PATTERNS OF REPRODUCTION IN FOUR LITTORINA SPECIES

The reproductive periodicities of four Iittorinids, Littorinaneglecta, L. nigrolineata, L. saxatilis and L. arcana were examinedin sympatric populations at Porth Swtan, Anglesey, North Wales.Three species, L. neglecta, L. nigrolineata and L. arcana, werefound to show marked reproductive periodicity. L. saxatilisshowed no periodicity and large numbers of animals were foundin breeding condition throughout the year. The oviparous speciesL. nigrolineata and L. arcana, came into reproductive conditionin the late summer or early autumn, L. nigrolineata in Augustand L. arcana in September, and their populations at Porth Swtanhad few individuals in breeding condition in the late springand early summer. L. neglecta, however, showed a periodicitywith high numbers of breeding animals throughout the springand summer and very low numbers in the autumn. For L. neglectathe basis of reproductive periodicity is shown to be the synchronizedannual life cycle of individuals of this species. It is thereforebelieved to differ from the other three species in which individualsare longer-lived and are supposed to undergo seasonal periodsof reproductive inactivity. (Received 2 March 1982;     

ALLOZYME SIMILARITY OF ATLANTIC AND PACIFIC SPECIES OF LITTORINA (GASTROPODA: LITTORINIDAE)

Four Littorina species from the Pacific (L. sitkana, L. brevicula,L. mandshurica, L. squalida) and four from the Atlantic (L.mariae, L. obtusata, L. saxatilis and L. littorea) were comparedelectrophoretically using 17 loci. Analysis of genetic identities showed that there were threegroups. The first group comprises L. sitkana, L. mariae, L.obtusata and L. saxatilis The second group consists of L. breviculaand L. mandshurica and the third one includes L. squalida andL. littorea. Our results support Reid's hypothesis of the originof Atlantic littorines from two Pacific ancestors. (Received 18 December 1991; accepted 30 March 1992)     

ALLOZYME COMPARISON OF LITTORINA SPECIES FROM THE NORTHWESTERN PACIFIC

Three unknown Littorina species were revealed by allozyme studyof snails from the northwestern Pacific. One of them was foundin Kasatka Bay (Pacific coast of Iturup Island, south KurileIslands) together with L. sitkana, which it resembled in anatomicalfeatures, but the genetic distance between these species wasD=0.622. The second one was found in Tauiskaya Inlet (northernpart of Okhotsk Sea) and was again similar to L. sitkana inmorphological and anatomical features, but D=1.160. The thirdspecies was found in Egvekinot Inlet (Anadyrskiy Gulf, BeringSea) in sympatry with L. natica, to which was close genetically(D=0.256) although it differed in shell shape. (Received 4 April 2005; accepted 26 August 2005)     

POPULATION GENETICS OF A SNAIL SPECIES COMPLEX IN THE BRITISH ISLES: LITTORINA SAXATILIS (OLIVI), L. NEGLECTA BEAN AND L. TENEBROSA (MONTAGU), USING SSCP ANALYSIS OF CYTOCHROME-B GENE FRAGMENTS

The intertidal snail Littorina saxatilis displays a range ofshell morphologies associated with a variety of habitats. Sincemorphology has an environmental and genetic basis, shell-basedtaxonomy may not accurately reflect genetic relationships. Weexplored genetic structure among adjacent populations of L.saxatilis (the robust open-shore type), L. neglecta (the tinybarnacle-dwelling type) and L. tenebrosa (the fragile brackish-watertype), at nine sites in Britain. Using single-strand conformationalpolymorphism analysis of a 375bp fragment of cytochrome-b wefound no evidence of species distinction. In AMOVA tests significantvariation was contained among populations (68%) and among individuals(32%, both P < 0.001), and insignificant variation was foundamong ecotypes. Genetic patterns suggested gene flow among ecotypesover small scales and a strong random input over larger scales. ^* To whom correspondence should be addressed. (Received 27 March 2000; accepted 10 July 2000)     

A GENETIC ANALYSIS OF SYMPATRIC SUBPOPULATIONS OF THE SIBLING SPECIES LITTORINA SAXATILIS (OLIVI) AND LITTORINA ARCANA HANNAFORD ELLIS

A detailed analysis of shell characteristics (four parameters)and allozyme allele frequencies (eight to nine polymorphic loci)of sympatric Littorina saxatilis and Littorina arcana subpopulationsfrom Filey Brigg on the east coast of England supports theiridentification as closely related but separate species. Oneenzyme system, esterase-2, was nearly species diagnostic. Resultswere generally comparable with an earlier study of the two speciesfrom East Lothian, Scotland. Littorina saxatilis was again foundto be more variable than L. arcana. (Received 14 December 1983;     

TENACITY OF ATTACHMENT IN TWO SPECIES OF LITTORINID, LITTORINA LITTOREA (L.) AND LITTORINA OBTUSATA (L.)

Here we present data concerning the ability of two littorinidsto remain attached to a slate substratum as a dislodging forceis applied vertically. Specimens of Littorina littorea (L.)and L. obtusata (L.) were attached to a simple pulley and sandflowsystem which applied force to the animals at a constantly increasingrate until the animals released from the substratum. Three aspectsof tenacity were measured: force required to remove the winklesfrom the substratum; time taken for removal; and final displacementat removal. For L. littorea the mean force required (1.09 N),the mean displacement (8.9 mm) and the mean time taken (185s) were all found to be significantly greater than those recordedfor L. obtusata (means = 0.60 N, 7.5 mm and 102 s, respectively).However, when animal size was taken into account there was nosignificant difference in either force or time required forremoval, although L. obtusata showed a greater displacementthan did L. littorea. Animal dry flesh weight was not a usefulpredictor of any of the tenacity variables. Rugosity of theslate substrata was shown to have a significant effect on alltenacity variables, greater forces being required to removeboth species of winkle from smooth substrata than from roughsubstrata. This also generally held true when animal size wasaccounted for. The results of these experiments, although insufficientto identify the mechanism(s) of attachment, do discount themechanism of ‘muscular grip’, since greater tenacitywould be expected on rough substrata. Whether winkles were immersedor emersed had no significant effect on any of the tenacityvariables. Recorded tenacities suggest that many L. littoreaand L. obtusata would be dislodged by the direct forces createdby breaking waves. (Received 5 August 1996; accepted 18 November 1996)     

THE GENETIC RELATIONSHIPS OF THREE TAXA IN THE LITTORINA SAXATILIS SPECIES COMPLEX (PROSOBRANCHIA: LITTORINIDAE)

Three species in the Littorina saxatilis complex (the ovoviviparousL. saxatilis and the two oviparous species L. arcana and L.nigrolineata) were screened for the products of up to 22 lociusing gel elec-trophoresis. Analysis of allele frequencies andderived genetic distances showed that, with rare exceptionsin L. saxatilis and L. arcana, conspecific populations clusteredtogether. Sympatric pairs of populations showed significantdifferentiation at many polymorphic loci. The results confirmedthe biological reality of the three taxa, and did not suggestthe existence of any previously unrecognized species. The speciesare genetically closely related to each other, with Nei geneticdistances ranging from 0.035 to 0.083. (Received 24 October 1989; accepted 18 April 1990)     

THE EARLY LIFE-CYCLE STAGES OF HYDROBIA VENTROSA AND HYDROBIA NEGLECTA WITH OBSERVATIONS ON POTAMOPYRGUS JENKINSI

The egg mass of Hydrobia neglecta contains a single egg, whilethat of H. ventrosa contains up to three eggs. At hatching H.neglecta has a significantly greater shell length than H. ventrosaand the late embryos and young snails of the two species canbe separated according to the pigmentation of the head region.The young snails can also be separated on the basis of surfaceornamentation of the shell and comparisons with the closelyrelated H. ulvae and Potamopyrgus jenkinsi show how the basicpattern of shell sculpturing differs in the four species. Thesedifferences are discussed in relation to the mode of development. (Received 14 February 1980;     

THE OLFACTORY-GUSTATORY BASIS OF FOOD PREFERENCE IN THE HERBIVOROUS PROSOBRANCH, LITTORINA LITTOREA (LINNAEUS)

Studies of food preference often measure the rate of consumptionof prey items by a predator; this confounds the factors determiningattractiveness and edibility, ignoring the fact that preferencesare probably resolved at the pre-ingestive stage of a consumer'sfeeding behaviour. In this paper, a novel technique has beendeveloped to measure the importance of chemical stimuli to feed,perceived by olfactory and gustatory means, as determinantsof the subsequent feeding behaviour of the generalist intertidalherbivore,Littorina littorea (L.). Cell-free extracts of a rangeof algae were presented simultaneously, impregnated in artificialcellulose-based substrates. Subsequent ranking of feeding preferencesreveals hierarchies which correspond with those establishedby other workers, using intact algae to feed L. littorea. Extractsof ephemeral early successional species (e.g. Ulva lactuca,Porphyra umbilicalis) generally provoke a more positive feedingresponse than perennial late successional species (e.g. Fucusvesiculosus, Asco-phyllum nodosum). Animals fed a preferredalga (Ulva lactuca) prior to preference trials displayed a reductionin the strength of preference relative to starved animals. Therewas no evidence of ‘switching’ of preference rankingsdue to satiation, however. These findings confirm the importanceof olfactory-and gustatory-mediated feeding behaviour as theprimary determinant of food preference in L. littorea. Theyare consistent with the hypothesis that the factors which determinethe attractiveness of a food type, such as chemical cues, arethe criteria by which consumers predict the value of that food.     

ESTERASE VARIABILITY IN THE GASTROPODS LITTORINA SAXATILIS (OLIVI) AND L. ARCANA ELLIS

The esterase system has been studied using isoelectric focusingin two closely related rough periwinkles, Littorina saxatilisand L. arcana, in an investigation of possible differences betweenthe two species at this level of discrimination. Collectionsof both species were obtained from Yorkshire, north Cornwalland south Devon; L. saxatilis was also obtained from sites insouth Cornwall (in and near the estuary of the Tamar), Dorsetand Scotland, where L. arcana was not present. There is considerablevariation both within and between sites which tends to maskany overall differences between the two species. However, ingeneral there is a much greater degree of heterogeneity withinsamples of L. saxatilis than within samples of L: arcana whenboth species are found together; this is reflected in the ShannonWiener diversity index for bands. Also the number of esterasebands is greater for L. saxatilis than for L. arcana at eachof the five sites where both occurred. A dendrogram derivedfrom the percentage occurrence of each band present in eachsample produced a reasonable degree of separation of the twospecies (Received 8 January 1988; accepted 24 February 1988)     

THE EGG MASS OF LITTORINA OBTUSATA AND LACUNA PALLIDULA (GASTROPODA : PROSOBRANCHIA)

The egg masses of Littorina obtusata and of Lacuna pallidulahave been compared with regard to size, shape, egg number, eggsize and substratum. The structure and histochemistry of thespawn of the two species has been investigated and observationson the laying process in L. obtusata are also recorded. ^* Present address: Portway School, Penpole Lane, Shirehampion,Bristol, BS11 0EB. (Received 12 October 1977;     

EMBRYONIC ABNORMALITIES IN POPULATIONS OF LITTORINA SAXATILIS (OLIVI) (GASTROPODA: PROSOBRANCHIA) IN THE WHITE SEA

The incidence of abnormally developing embryos in brood pouchesof females was studied in five populations of Littorina saxatilisliving under different salinity conditions. The proportion ofabnormals decreased during embryonic development. Age of femaleand infection with the ciliate Protophrya ovi-cola had no effecton the frequency of abnormals. The proportion of abnormal eggs(PAE) increased at the end of the reproductive season; a similartrend was found for the proportion of abnormal veligers (PAV)although it was not always significant. The proportion of abnormaljuveniles (PAJ) showed no seasonality. The increase of PAE coincidedwith decrease of water temperature in September. Environmentalsalinity was significantly correlated with frequency of abnormalsin L. saxatilis populations: the highest values of PAV and PAJwere observed in estuarine population (salinity range 5–8%),intermediate in populations living under conditions of 10–20%osalinityand lowest in control populations (23–24%). Itis suggested that critical salinity (sensu Khle-bovich, 1974)(approximately 8–10%) may also be a crucial point forstability of embryonic development in the White Sea populationsof L. saxatilis. (Received 28 June 1994; accepted 28 November 1994)     

THE ROLE OF LYMNAEA AURICULARIA (LINNAEUS) AND LYMNAEA PEREGRA (MULLER) (GASTROPODA: PULMONATA) IN THE TRANSMISSION OF LARVAL DIGENEANS IN THE LOWER THAMES VALLEY

Eleven species of larval digeneans are reported for the firsttime in the UK from the freshwater snail Lymnaea (Radix) auricularia.The latter replaced its congener L. peregra in a gravel pitnear Wraysbury, Berkshire in the Lower Thames Valley and hostedan assemblage of larval digeneans similar to that previouslytransmitted by L peregra. The larval digeneans of L. peregrain small bodies of water in the area were also similar to thosefound in L. auriculania in the gravel pit. This replacementin the role of the host is explained on the basis of morphological,physiological and ecological similarities of the two lymnaeidspecies. (Received 19 February 1992; accepted 27 April 1992)     

FACTORS CONTRIBUTING TO SPATIAL HETEROGENEITY IN THE ABUNDANCE OF THE COMMON PERIWINKLE LITTORINA LITTOREA (L.)

Although Littorina littorea (L.) exhibits a relatively consistentpattern of vertical distribution throughout the North Atlantic,ranging from the mid-intertidal to the shallow subtidal zone,its horizontal distribution and abundance are highly variable.In this study, we first described the snail's horizontal distributionpatterns on Appledore Island, ME, USA and then asked whetherwave exposure, rugosity, predator density (e.g. Carcinus maenasand Cancer borealis), the percentage of the substrate coveredby Ascophyllum nodosum, Chondrus crispus, Polysiphonia spp.,and ephemeral green algae, or the percentage of uncovered substrate(bare rock) were correlated with L. littorea abundance in theintertidal zone (0.6 to 0.0 m relative to Mean Lower LowWater [MLLW]) and the shallow subtidal zone (–1.5 to –3.0 mMLLW) at nine study sites. Intertidal densities of L. littoreawere highly variable across sites, ranging from 0 to >600 m^–2.In this zone, L. littorea density showed a significant positivecorrelation with rugosity and percentage of bare rock. Densitieswere very low in the subtidal zone (range: 0–19 m^–2)and varied little among sites. Exploratory multiple regressionanalysis suggested that L. littorea density was positively correlatedwith the density of C. maenas in the shallow subtidal zone.Additionally, snails in the subtidal zone had thicker shellsthan snails of the same size in the intertidal zone. Our resultssuggest that structural elements of the habitat, such as rugosityand percentage of uncovered substrate, are among the most importantpredictors of L. littorea abundance on moderately protected,rocky intertidal shores. (Received 9 February 2005; accepted 10 August 2005)     

THE SYSTEMATIC POSITION OF LAROCHEA FINLAY, 1927, AND INTRODUCTION OF A NEW GENUS AND TWO NEW SPECIES (GASTROPODA: SCISSURELLIDAE)

Species of the gastropod genus Larochea Finlay, 1927 are shownto be scissurellids without an anal shell slit or foramen. TheNew Zealand species, L. miranda Finlay, 1927 and L. secundaPowell, 1937, brood their young in the right subpallial cavityagainst a modified inner lip that is set well behind the aperturalplane. Larochea scitula n.sp. is based on shells from WanganellaBank, southern Norfolk Ridge. Larocheopsis n. gen. is introducedfor a minute species from off northern New Zealand that lacksa shell brood chamber. Larochea miranda and Larocheopsis amplexan.sp. are either gonochoristic with smaller males or consecutivehermaphrodites, while Larochea secunda and L. scitula are evidentlygonochoristic, having mature males and females of similar size. (Received 23 July 1992; accepted 10 December 1992)     

CHROMOSOME NUMBER IN TWO PHENOTYPICALLY DISTINCT POPULATIONS OF LITTORINA SAXATILIS OLIVI, AND IN SPECIMENS OF THE LITTORINA OBTUSATA (L.) SPECIES-COMPLEX

Chromosome numbers counted from embryo cells of the marine gastropodLittorina saxatilis (=L. rudis), were the same, 2n = 34, inpopulations of two different phenotypes from a small area inSweden. Chromosome number in the related species-complex, Littorinaobtusata, could not be determined definitely, but the most adequatefigure seemed to be 2n = 34. (Received 9 September 1982;     

MORPHOLOGICAL DIVERGENCE AND EVIDENCE FOR REPRODUCTIVE ISOLATION IN LITTORINA SAXATILIS(OLIVI) IN NORTHEAST ENGLAND

Current work at Old Peak (Ravenscar) on the northeast coastof England indicates that boulder-dwelling Lutonna saxatilis(Olvi) comprise at least two distinct forms, inhabiting high-and mid-shore boulders Using multivariate morphometrics we showthat these forms are significantly different in shape. Rareintermediates between these two distinct forms were occasionallyfound, usually with the low shore animals The two forms showdifferent reproductive strategies. High shore females (L. saxatilisH) mature at a smaller size and produce a smaller number oflarge eggs giving rise to large crawlaways The mid-shore form(L. saxatilis M) matures at a larger size and produces a largenumber of small eggs which give rise to small crawlaways. Anovel observation is that intermediate females (L. saxatilisI) contain eggs of both sizes, giving rise to a bimodal distributionof egg sizes within the brood pouch. The usual incidence ofabortion (observed in H and M forms) is Very low (<1%) However,in the intermediates the large eggs showed a high incidenceof abortion (about 60%) and the incidence of abortion in thesmall eggs was also increased (about 30%) Thus there appearsto be a partial reproductive barrier between the two forms,presumably resulting in reduced fitness due in the intermediatesto reproductive dysfunction. These findings extend to othershores in the region, over total distance of about 66 km. Thefacts are suggestive of a hitherto unrecognised reproductivebarrier with L. saxatilis, the nature and strength of whichis under investigation ^*Present address: University College Scarborough. Filey Road.Scarborough Yo11 3AZ. (Received 12 June 1995; accepted 15 September 1995)     

COMPARATIVE LIFE-CYCLE, BIOMASS AND SECONDARY PRODUCTION OF THREE SYMPATRIC FRESHWATER GASTROPOD SPECIES

The life cycles, biomass and secondary production of three sympatricfreshwater basommatophoran snails, Lymnaea palustris (MÜller),Physa fontinalis Linnaeus and Anisus rotundatus (Poiret) werestudied during two years in a freshwater ditch. L. palustrisexhibited an iteroparous life-cycle whereas the two other speciespresented a semelparous life-cycle, adults died just after oviposition.L. palustris secondary production (dry weight) value was higher(P = 11 298.4 mg 0.1 m^–1 yr^–1) than those of P.fontinalis (P = 846.3 mg 0.1 m^–2 yr^–1) and A. rotundatus(P = 1192 mg 0.1 m^–2 yr^–1). (Received 16 March 1992; accepted 30 June 1992)     

VARIATIONS IN INFESTATIONS OF SIPHONARIA CAPENSIS AND S. CONCINNA(PULMONATA) BY LARVAL TREMATODES IN SOUTHERN AFRICA

The prevalence of digenean trematode parasites in Siphonariacapensis (Pulmonata) was examined in populations from 24 sites,and in S. concinna from 10 sites along the coast of southernAfrica from 1989 to 1991. Sporocysts containing cercariae werefound in the digestive gland of both species. To date, two typesof cercaria have been isolated from S. capensis and one typefrom S. concinna, these types possibly representing three distinctspecies of trematode. In approximately 30% of parasitized S.capensis and 10% of parasitized S. concinna the digestive glandwas completely destroyed. In both species of Siphonaria therewas considerable temporal and spatial variation in parasiteprevalence. At some locations up to 40% of S. capensis wereinfected whereas at others, no parasites were found. Prevalenceof trema-todes in S. concinna rarely exceeded 12%. At severalsites the prevalence of infestation within the limpets increasedwith increasing host size. (Received 8 June 1992; accepted 6 July 1992)