STRUCTURE OF THE CONCHIOLIN CASES OF THE PRISMS IN MYTILUS EDULIS LINNE

The prisms in the shell of Mytilus edulis Linné are calcite needles. Their small size and their thin conchiolin cases distinguish them from the prisms of many other species of mollusks. These Mytilus prisms have been studied with the electron microscope. The material consisted of positive replicas of surfaces of the prismatic layer, etched with chelating agents, and of preparations of tubular cases from decalcified prisms which were compared with the conchiolin from decalcified mother-of-pearl of the same species. In the replicas, the cases appear as thin pellicles in the intervals between the prism crystals. Both the prism cases and the nacreous conchiolin, disintegrated by exposure to ultrasonic waves and sedimented on supporting films, appear in the form of tightly meshed, reticulated sheets, described as "tight pelecypod pattern" in former studies on nacreous conchiolin of Mytilus. The results show that in the shell of this species the same conchiolin structure is associated with aragonite in mother-of-pearl and with calcite in the prismatic layer.     

BENTHIC METABOLISM ON A SHELTERED ROCKY SHORE: ROLE OF THE CANOPY IN THE CARBON BUDGET1

While the importance of canopy‐forming algae in structuring ecosystems is recognized, their role in the carbon budget is still not well understood. To our knowledge, no measurements of rocky shores primary production and respiration under emersion periods have been carried out in situ. A benthic chamber coupled to a CO₂‐infrared gas analyzer was used to measure gross primary production and respiration on the Ascophyllum nodosum (L.) Le Jol. zone of a sheltered rocky shore in Brittany, France. Over a year of monthly measurements on the zone with and without the A. nodosum canopy showed fairly high production and respiration values for the global community as well as carbon fluxes due to the canopy that largely dominated the benthic metabolism of the zone. The strong canopy respiration relative to the primary production also suggested a high metabolic activity by microscopic heterotrophs on the surface of the alga. Both the canopy and the understory annual primary production and respiration were under the control of light and temperature seasonal variations. Finally, the range of the amount of carbon produced on the A. nodosum zone during diurnal emersions was estimated. Additional measures accounting for the day–night cycles and seasonal light variations over an entire tidal cycle are, however, necessary to establish an annual carbon budget. Such measures using the benthic chamber together with complementary techniques would allow a better understanding of the functioning of sheltered rocky shores.     

THE METACHRONAL WAVE OF LATERAL CILIA OF MYTILUS EDULIS

The form of beat of cilia and the structure of the metachronal wave on the lateral gill epithelium of Mytulus edulis have been studied on living material by interference-contrast microscopy and stroboscopic illumination, and compared with the same features in rapid-fixed preparations studied by light microscopy and with the scanning electron microscope. The most striking finding is that the beat of the cilia is not planar, as previously assumed, but involves a sideways movement in the recovery stroke Previous reports on nonplanar ciliary beating from protozoan examples describe a planar effective stroke and a counterclockwise rotation in the recovery stroke; in this molluscan example there is a clockwise rotation in the recovery stroke The lateral inclination of the cilia in the recovery stroke is in the same direction as the propagation of the waves, and the orientation of cilia in the recovery stroke is thought to determine whether the waves move to the left or right of the direction of the effective stroke     

锌-65从三角褐指藻向紫贻贝传递的初步实验研究

从~(65)Zn为示踪元素,进行了~(65)Zn从褐指藻到贻贝的传递实验。实验进行了5天。结果表明:(1)贻贝从藻中累积锌的能力比直接从海水中累积锌的能力高41.5～72.0倍;(2)~(65)Zn从褐指藻到贻贝有明显的传递,实验第5天时的传递比率为6.18％;(3)在实验过程中,贻贝体内锌的贪量从未超过藻中的锌含量。     

EXCLUSION OF THE ROLE OF SECONDARY CONTACT IN AN ALLELE FREQUENCY CLINE IN THE MUSSEL MYTILUS EDULIS

We examined the hypothesis that secondary contact generates an allele-frequency cline at the aminopeptidase-I locus (Lap) in the marine mussel, Mytilus edulis. It has been proposed that variation at the Lap locus is neutral and that the cline results from secondary contact between differentiated oceanic and estuarine populations (Levinton, 1980). We tested this hypothesis by comparing the genotypic distributions in samples from the cline to distributions that incorporate mixing effects. We employed a statistical model that determines the degree of contact using a maximum likelihood estimator and then incorporates the mixing estimates into an expected distribution of genotypes. Wahlund effects resulting from possible admixture are thereby incorporated into the expected distribution. Failure of the model to reconcile the observed with the expected distribution of genotypes indicates that the observed population structure does not result from admixture. The null hypothesis of mixing was unable to explain about 33% of the samples. Combined tests demonstrated the general departure from the mixing model to be highly significant. The distribution of heterozygote discrepancies across the cline was inconsistent with the expectations of a mixing model. Therefore we reject explanations for the structure of the Lap cline that involve secondary contact. Selection directed at the Lap locus appears necessary to explain the genotypic structure of clinal populations.     

WING SHAPE VARIATION ASSOCIATED WITH MIMICRY IN BUTTERFLIES

Mimetic resemblance in unpalatable butterflies has been studied by evolutionary biologists for over a century, but has largely focused on the convergence in wing color patterns. In Heliconius numata, discrete color‐pattern morphs closely resemble comimics in the distantly related genus Melinaea. We examine the possibility that the shape of the butterfly wing also shows adaptive convergence. First, simple measures of forewing dimensions were taken of individuals in a cross between H. numata morphs, and showed quantitative differences between two of the segregating morphs, f. elegans and f. silvana. Second, landmark‐based geometric morphometric and elliptical Fourier outline analyses were used to more fully characterize these shape differences. Extension of these techniques to specimens from natural populations suggested that, although many of the coexisting morphs could not be discriminated by shape, the differences we identified between f. elegans and f. silvana hold in the wild. Interestingly, despite extensive overlap, the shape variation between these two morphs is paralleled in their respective Melinaea comimics. Our study therefore suggests that wing‐shape variation is associated with mimetic resemblance, and raises the intriguing possibility that the supergene responsible for controlling the major switch in color pattern between morphs also contributes to wing shape differences in H. numata.     

贻贝(Mytilus edulis)核型及染色体带型分析

本文对贻贝染色体进行了核型分析,其结果为：２ｎ＝２８,１２ｍ＋１０ｓｍ＋６ｓｔ,ＮＦ＝５０,ＴＣＬ＝ １０３．９０μｍ,ＣＬ：２．７３５－４．７７４μｍ。第１、２、４、８、１１、１２对为中部着丝粒染色体（ｍ）;第６、９、１０、１３、１４对 为亚中部着丝粒染色体（ｓｍ）;第 ３、５、７对为亚端部着丝粒染色体（ｓｔ）。对贻贝染色体的Ｇ带、Ｃ带、银 染带进行了分析。银染结果表明,贻贝细胞中有四个银染核仁组织区（Ａｇ－ＮＯＲｓ）,分布在第 ３、５对染 色体长臂末端。     

COMPARATIVE ANALYSIS OF KARYOTYPES AND NUCLEOLAR ORGANIZER REGIONS IN DIFFERENT POPULATIONS OF MYTILUS TROSSULUS, MYTILUS EDULIS AND MYTILUS GALLOPROVINCIALIS

The cylotaxonomical characteristics of Mytilus tros-sulus, M.edulis and M. galloprovincialis were studied using karyometricanalysis and silver staining. The karyotype of M. trossulus,reported here for the first time, consists of six metacentricand eight submetacentric-subtelocentric chromosome pairs. Theoccurrence of five metacentric chromosome pairs in M. galloprovincialisdifferentiates this taxon from M. trossulus and M. edulis whichboth have six meta-centrics. The number of submetacentric tosubtelo-centric chromosome pairs was variable between populationsand between taxa. We suggest that this variability has arisenfrom differential chromosome condensation rather than from structuralchange. Intercomparison of chromosome relative length showedstrong similarity among the three taxa. Chromosomal nucleolarorganizer regions (NORs) were identically located on two submetacentric-subtelocentricchromosome pairs in all three taxa. However, M. trossulus showeda characteristic difference in the occurrence of NORs on onemetacentric pair, which was absent in M. galloprovincialis andM. edulis. Variability in the number of NORs per cell was observedin all populations studied. We conclude that the three taxaof Mytilus studied here cannot be differentiated by asinglekaryological character, but that a combination of karyologicalcharacters is virtually diagnostic ^* To whom correspondence should be sent (Received 24 January 1994; accepted 9 March 1994)     

SOME ECOLOGICAL ASPECTS OF THE FEEDING BEHAVIOUR OF THE OYSTERCATCHER HAEMATOPUS OSTRALEGUS ON THE EDIBLE MUSSEL MYTILUS EDULIS

Oystercatchers have two methods of opening mussels, both neatly adapted to the structure of the prey. To open mussels exposed by the tide, the bird hammers a hole along the ventral margin of the shell, whereas to open mussels under water, the bird drives its bill into the gape of the valves to cut through the posterior adductor muscle. Large and strong-shelled mussels can be opened by stabbing but not by hammering. Feeding methods of Oystercatchers vary from mussel-bed to mussel-bed. These variations in behaviour are attributable to differences in the strength of the shells of the prey and to the firmness of their attachment to the substrate. Diversity of ecological conditions on the mussel-beds causes an apparent size selection of prey by Oystercatchera.     

THE ACROSOME REACTION IN MYTILUS EDULIS : I. Fine Structure of the Intact Acrosome

The intact acrosome of the Mytilus edulis spermatozoon consists of a conical vesicle, the basal side of which is deeply invaginated so that the whole vesicle forms a sheath around a very slender axial rod, about 2.7 µ long, inserted in a tube passing through the nucleus. The annular base of the acrosomal vesical is filled with a homogeneous substance; the outer wall of the vesicle is lined with a somewhat irregular layer of a particulate substance interspersed with very fine tubular elements, and its lumen is nearly filled by a strand of material which extends from the inner tip of the invagination to the apex of the acrosome. The lumen of the invagination appears empty except for the rod and a delicate sleeve-like structure which surrounds it. The plasma membrane of the sperm cell lies in immediate contact with the acrosomal membrane over its whole outer surface. In its general organization, this molluscan acrosome shows a rather close homology with that of the annelid Hydroides.     

MORPHOLOGICAL AND ALLOZYMIC VARIATION IN POPULATIONS OF MYTILUS GALLOPROVINCIALISFROM THE AEGEAN SEA

Eight populations of Mytilus galloprovincialis from differentcoasts of the Northern and Central Aegean Sea have been investigatedat the morphological and allozymic level. A significant degreeof variation was found within and among the populations. Theaverage degree of heterozygosity ranges from 0.085 to 0.14 andit is lower than those reported for other populations of thesame species. No correlation was found between the degree ofheterozygosity and the morphological variability among the populationsexamined. (Received 14 May 1992; accepted 1 October 1992)     

THE INFESTATION OF MYTILUS EDULIS LINNAEUS BY POLYDORA CILIATA (JOHNSTON) IN THE CONWY ESTUARY, NORTH WALES

The incidence of the shell-boring parasite Polydora ciliatain Mytilus edulis from the Conwy estuary, North Wales is described.Amongst mussels >40 mm in shell length both the occurrenceand abundance of P. ciliata increased steeply with host size.Infestation was highest amongst mussels near the mouth of theestuary where around 60–65% of the population was parasitized;no systematic relationship between the incidence of P. ciliataand tidal elevation was observed. Mussel condition was negativelycorrelated with the degree of infestation. Moderately and heavilyinfested mussels, however, never accounted for more than ca.10% of this population and the overall detrimental effects ofP. ciliata on growth and production is thus probably quite small.Whilst heavily infested mussels were evidently more vulnerableto predation, the shore crab, Carcinus maenas, selected smaller,non-infested mussels whenever these were available. No obviousrelationships were found between the presence of P. ciliataand the incidence of either pearls or pea crabs. (Received 14 January 1991; accepted 2 April 1991)     

A PLANIMETRIC STUDY OF MORPHOLOGICAL VARIABILITY IN THE DIGESTIVE DIVERTICULA OF LITTORINA LITTOREA (LINNAEUS) AND MYTILUS EDULIS LINNAEUS

The inter-and intratubular morphological variability in thedigestive diverticula of Littorina littorea and Mytilus edulishas been investigated by planimetric procedures. Five parametershave been measured: mean epithelial thickness (MET), mean diverticularradius [MDR], mean luminal radius (MLR), MLR/MET ratio and MET/MDRratio. The results indicate that irrespective of the patternof tubule organization within the digestive diverticula (whethertubule types are clustered or not), variability between individualsis greater than that between zones of the digestive gland. Thishas implications for the design of sampling strategies in investigationsof the morphology of digestive diverticula in physiologicaland pathological studies. The variability in the epithelialthickness within diverticular sections is of minor relevancein assessing the overall condition of the digestive gland inthese studies, because variability in epithelial thickness betweentubules is significantly greater than within tubules in bothspecies. (Received 10 March 1989; accepted 16 October 1989)