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;     

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)     

BARNACLE-DWELLING EGOTYPES OF THREE BRITISH LITTORINA SPECIES AND THE STATUS OF LITTORINA NEGLECTA BEAN

On the basis of collections from SW Wales and W Ireland it isshown that small (<5 mm) black and/or white Littorina occurringin the barnacle zone on exposed shores, of the L. neglecta shelltype, comprise three species. From their reproductive anatomythese correspond to L. saxatilis, L. arcana and L. nigrolineata,and are interpreted as analogous barnacle-dwelling ecotypesof these species. This adds to the evidence that L. neglectais not a distinct species, but an ecotype of L. saxatilis. (Received 1 June 1992; accepted 23 June 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)     

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)     

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;     

CHROMOSOMES OF MELANOPSIS DUFOURI FERUSSAC, 1823 (CAENOGASTROPODA: MELANOPSIDAE)

The most frequent chromosome numbers were 2n = 36 and n = 18in Melanopsis dufouri Férussac inhabiting the Ullal deBaldovi, an ancient spring of the Albufera lake (Valencia province),and the small stream Rambla de Gaibiel (Castellon province)in Spain. Subtelocentric and subtelo-telocentric chromosomespredominated in the sets of snails from both populations. Pericentricinversions were basic factors in the interpopulational differentiationof karyotypes. Intrapopulational karyotype polymorphism (specimenswith 2n = 36, 2n = 34, rarely 2n = 35) and mosaic molluscs occurredin the Ullal de Baldovi population as a result of small chromosomeelimination. The rather frequent appearance of one or two non-homologuesmall chromosomes in hypodiploid nuclei 2n = 35, 2n = 34 wasobviously connected with fragmentation of chromosomes. Karyologicalfindings are in accordance with phenotypic diversity of M. dufourifrom the Ullal de Baldovi population. (Received 27 February 1997; accepted 10 October 1997)     

Confirmation of Ancient Polyploidy in Dahlia (Asteraceae) Species using Genomic In Situ Hybridization

The successful production of interspecific hybrids between membersof the dysploid chromosome series inDahlia offers a unique opportunityto investigate chromosome evolution. Analysis of meiotic metaphaseI in these hybrids using genomic in situ hybridization (GISH)has shown that pairing occurs both between and within parentalgenomes. These results have provided clear evidence for theallotetraploid origin of Dahlia species with 2n=32 and suggeststhat species with 2n=34 and 2n=36 have also arisen via allopolyploidy.A bivalent promoting mechanism proposed for species with 2n=32also appears to be present in Dahlia species with 2n=34 and2n=36 .Copyright 1999 Annals of Botany Company Dahlia , GISH, dysploidy, chromosome pairing, karyotype analysis, polyploidy.     

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)     

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)     

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)     

MICRODISTRIBUTION IN THE FIELD AND HABITAT CHOICE IN AQUARIA BY COLOUR MORPHS OF LITTORINA MARIAE SACCHI & RASTELLI

The microdistributions of yellow and brown morphs of adult andjuvenile Littorina mariae were investigated in the field onFucus plants. On F. vesiculosus in autumn, yellow adults werefound more frequently than expected on laminae and brown adultsmore frequently than expected on stipes. In spring there wasno difference in distribution between adult morphs. There wasno difference in microdistribution betweenjuvenile morphs oneither F. vesiculosus or F. serratus in autumn. Yellow and brown adults were allowed to choose between an artificialbrown and an artificial yellow background, and between stipeand lamina of F. serratus in aquarium experiments. Both morphspreferred the yellow rather than the brown background. In mostcases, the morphs climbed upwards on F. serratus, regardlessof algal orientation (lamina upwards or stipe upwards) or lightregime (lights on or off). A significant difference in microdistributionbetween morphs was found with the lamina placed upwards andthe lights on. Brown snails then preferred stipe, while yellowsnails did not show a preference for either stipe or lamina. (Received 16 June 1994; accepted 31 October 1994)     

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)     

Cytological Observations on Three British Species of Laminaria : a Preliminary Report

Mitotic divisions in male and female gametophytes and in youngsporelings of Laminaria digitata, L. ochroleuca, and L. saccharinafrom Plymouth follow a normal course and do not show the ‘endomitoticmultiplication’ of chromosomes described by Walker inL. digitata from Scotland. Chromosome counts on all three speciesalmost invariably give a value for n between 27 and 31, anda definite count of this order will probably emerge.     

ON THE OCCURRENCE OF THE PROSOBRANCHS LITTORINA NERITOIDES, L. MARIAE AND L. OBTUSATA IN DENMARK

Littorina neritoides occurs on piers and large stones on thebeaches in northern Jutland, but may not be able to toleratecold winters. L. obtusata and L. mariae are common on Fucus,but only L. mariae penetrates deeply into the fjords and sounds. (Received 10 December 1979;     

VARIATION IN THE OCCURRENCE OF ABNORMAL EMBRYOS IN FEMALES OF THE INTERTIDAL GASTROPOD LITTORINA SAXATILIS OLIVI

The incidence of abnormally developed embryos within the brood-pouchof female L. saxatilis was very variable, ranging from 0–100%of embryos being abnormal. A minor part of the total variationwas attributed to between-shore variation, while 82% reflectedwithin sample differences between females. Possible factorsresponsible for the variation in embryo abnormality shown bythis and other investigations, are discussed and it is concludedthat genetic rather than non-genetic factors are important. (Received 8 November 1983;     

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 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.     

NEW BASIC CHROMOSOME NUMBERS FOR GENERA OF NEOTROPICAL FERNS

Chromosome numbers for eight genera of Costa Rican ferns are reported here for the first time. These are: Neurocallis, n = 58; Marginariopsis, n = 35; Dicranoglossum, n = 36; Glyphotaenium, n = 37; Cochlidium, n = 33; Ormoloma, n = 42; Peltapteris, n = 40; and Loxsomopsis, n = 46. Chromosome observations involving several other genera are included: Solanopteris, n = 37; Xiphopteris, n = 32; Hemidictyum, n = 31: Pleuroderris, 2n = 80; Dictyoxiphium, 2n = 80; and Polystichum, n = 41. These numbers are compared to those of genera of presumed taxonomic affinity.     

THE ORIGIN OF AGROPYRON SMITHII

The hypothesis that North American octoploid Agropyron smithii Rydb., 2n = 56, originated by hybridization between tetraploid Agropyron and Elymus species, followed by chromosome doubling, was tested by observing chromosome pairing in hybrids of A. smithii with an induced amphiploid, 2n = 56, derived from E. canadensis L., 2n = 28, X E. dasystachys Trin., 2n = 28, F₁'s. Chromosome pairing in A. smithii averaged 0.52^I, 27.70^II, 0.01^III, and 0.01^IV in 184 metaphase-I cells; and the amphiploid averaged 1.13^I and 27.44^II in 195 cells. Chromosome pairing in A. smithii X amphiploid hybrids averaged 8.20^I, 23.38^II, 0.34^III, and 0.05^IV in 101 metaphase-I cells. It was concluded that A. smithii was genomically similar to the E. canadensis-E. dasystachys amphiploid. The basic genome formula of the amphiploid is SSHHJJXX, with the SSHH genomes coming from E. canadensis and the JJXX genomes coming from E. dasystachys. Consideration of the morphological, ecological, and reproductive characteristics of all North American species that contain the basic SSHH and JJXX genomes led to the conclusion that A. dasystachyum (Hook.) Scribn., SSHH, and E. triticoides Buckl., JJXX, are the probable progenitors of A. smithii.