Competition for the home and aggressive behaviour in the chiton Acanthopleura gemmata (Blainville) (Mollusca: Polyplacophora)

Summary Computerized screening of all the positions recorded during a synodic month on 120 individually marked chitons (Acanthopleura gemmata) pinpointed their preferential resting points. Unlike the majority of intertidal chitons so far studied, A. gemmata rests in well-defined homes actively dug in the rock. Homes proved to be not strictly individual and periodically interchangeable. A complex aggressive behaviour was recorded in the field when two animals came in contact at home. When competing for ownership of a resting site rival chitons may suppress their nocturnal feeding activity. Despite its strong home-related territoriality A. gemmata showed no mutual exclusion on the feeding area. The highly specialized resting habits clearly protects A. gemmata from its most important predator, the toad fish Arothron immaculatus. The behaviour of A. gemmata is compared to that of other chitons and gastropods, and the current hypotheses concerning the adaptive value of the homing behaviour in littoral molluscs are discussed.     

Spread ofCyclope neritea (Mollusca: Gastropoda) along the north-eastern Atlantic coasts in relation to oyster culture and to climatic fluctuations

The geographic distribution ofCyclope neritea (Linné) (Mollusca: Gastropoda) along the Atlantic coasts of Portugal, Spain and France is reported. Analysis of information published over the last 90 yr indicates that, since 1983,C. neritea has extended its range northwards from Arcachon Bay along the coast of the Bay of Biscay. The spread of this small gastropod is directly related to the commercial transport of the Pacific cup oyster (Crassostrea gigas Thunberg) to the Atlantic from Mediterranean oyster-culture sites, and to its encountering climatic conditions suitable for its settlement and reproduction in its new habitat. Its transport by human intervention explains the rapid spread ofCyclope neritea during 1983 and 1984, despite its lack of a planktonic stage or of effective natural migration by adults. Climatic conditions in the southern parts of the Bay of Biscay are similar to those of the French Mediterranean lagoons, explaining the easy acclimatization of this eurythermic gastropod. Also, coastal air and sea-surface temperature records over the last two decades (1971–1988) have revealed a slight warming of the southern parts of the Bay of Biscay. This has resulted in a more strongly marked latitudinal thermal gradient along the Bay of Biscay and has furthered survival and reproduction ofCyclope neritea emigrants. A detailed analysis of commercial supplies of cup oysters to the Bay of Biscay from the Mediterranean coast indicates that theC. neritea emigrants undoubtedly originated from the salt-water lagoons of Salse-Leucate and Thau (French Mediterranean coast).     

A molecular phylogeny of the Patellogastropoda (Mollusca: Gastropoda)

Phylogenetic analyses of partial 18S rDNA sequences from species representing all living families of the order Patellogastropoda, most other major gastropod groups (Cocculiniformia, Neritopsina, Vetigastropoda, Caenogastropoda, Heterobranchia, but not Neomphalina), and two additional classes of the phylum Mollusca (Cephalopoda, Polyplacophora) confirm that Patellogastropoda comprises a robust clade with high statistical support. The sequences are characterized by the presence of several insertions and deletions that are unique to, and ubiquitous among, patellogastropods. However, this portion of the 18S gene is insufficiently informative to provide robust support for the monophyly of Gastropoda, or to address the division of the Gastropoda into the subclasses Eogastropoda (= Patellogastropoda + hypothetical coiled ancestors) and Orthogastropoda. These sequence data invariably group Patellogastropoda in a weakly supported clade with cocculiniform limpets, despite greater sequence divergences between Patellogastropoda and “Cocculiniformia” than between the Patellogastropoda and Orthogastropoda. Partial 18S sequences support the inclusion of the family Neolepetopsidae within the superfamily Acmaeoidea, and refute its previously hypothesized position as sister group to the remaining living Patellogastropoda. This region of the 18S rDNA gene diverges at widely differing rates, spanning an order of magnitude among patellogastropod lineages, and therefore does not provide meaningful resolution of the relationships among higher taxa of patellogastropods. Data from one or more genes that evolve more uniformly and more rapidly than the 18S rDNA gene (possibly one or more of the mitochondrial genes) seem more likely to be informative about relationships within Patellogastropoda. Received: 5 February 1999 / Accepted: 16 May 2000     

Chemical defense and evolution in the Sacoglossa (Mollusca: Gastropoda: Opisthobranchia)

Summary. Recent advances in both the systematics and the natural products chemistry of the order Sacoglossa (=Ascoglossa) in the gastropod subclass Opisthobranchia suggest a revised and improved historical account of the evolution of the group. Although the algal genus Caulerpa makes a suitable model for the ancestral food of the order, other siphonaceous algae are consistent with both morphological and chemical data. At an early evolutionary stage terpenoids are sequestered from the food, and used defensively, often with modification. With an evolutionary switch to different kinds of algal food, there is often a shift to other, related defensive chemicals. A switch to new food source sometimes leads to the abandonment of chemical defense, but in other cases there is de-novo synthesis of defensive metabolites. The synthesis of polypropionates, which are used defensively, occurs in some other gastropods, but otherwise is known only in fungi. The systematic distribution of the defensive polypropionates suggests that their defensive use has evolved several times among gastropods. Failure to detect them may mean that synthetic capacity has evolved more than once, or it may mean that they exist at low levels, perhaps having a non-defensive function. Received 9 February 1998; accepted 20 March 1998.     

Density-dependent mortality of recruits of the abaloneHaliotis rubra (Mollusca: Gastropoda)

In three wild populations ofHaliotis rubra surveyed off southeastern Australia during the three years 1987–1989, 0 to 10% post-settlementH. rubra survived for 5 mo. Sequential censuses (February, May and December in each year) provided evidence that mortality of post-settlementH. rubra increased with the density of settlement. The occupation of cryptic habitat byH. rubra soon after settlement may well be an adaptation for avoiding predators or grazers and dislodgement by violent water movement.     

Intertidal distribution and long-term movements of Littorina irrorata (Mollusca: Gastropoda)

The distribution of Littorina irrorata Say on a low-energy barrier beach on the northern Gulf of Mexico is described, and correlated with the presence of Spartina alterniflora and other plants in the upper intertidal zone. The movements of 66 individually tagged snails were followed in the S. alterniflora zone for an average of 226 days, during which time an average of 10.6 positions were recorded per snail. The snails travelled an average total path distance of at least 995 cm, but due to contorted paths, ended up an average resultant distance of only 399 cm away from their original positions. They moved an estimated resultant distance of approximately 20 to 25 cm per activity period. Despite a slight offshore movement during the fall and winter, the snails moved more parallel to the shoreline than perpendicular to it.     

Homing to scars as a defense against predators in the pulmonate limpet Siphonaria gigas (Gastropoda)

The length of larval life in some coral reef fishes was estimated from the number of growth increments in the otoliths of newly settled fishes. We examined 210 individuals comprising 38 species and 5 unidentified taxa, and belonging to 12 families. During 2 successive austral summers (1976–1977 and 1978–1979), specimens were collected from the lagoon at One Tree Reef, Great Barrier Reef, Australia. By assuming that growth increments in otoliths are laid down on a regular daily cycle commencing near the time of hatching, we calculated typical ages ranging from 3 to 6 wk with a minimum of just over 2 wk and a maximum of 12 wk. The otoliths also contain distinctive microstructural features which can serve as approximate temporal markers for the change from the postlarval to juvenile life stage.     

Spawning behaviour and egg capsules of Concholepas concholepas (Mollusca: Gastropoda: Muricidae)

Observations on the spawning behaviour of the commercially important muricid snail Concholepas concholepas are reported. The sequence of events relating to external transportation, molding and hardening, and attachment of the egg capsules to a substratum were timed and divided into 6 major events. The snails studied in the laboratory spawned between April and Septemer. These results and data from the literature reveal an all-year-round spawning activity for the species. The frequency, size and time of spawning were studied over 1 year. Spawning activity always began at night, suggesting that the species retains its spawning rhythm in the laboratory. These was a direct relationship between length of the snail and size of the capsules spawned. No nutritive eggs were found; the number per capsule varied between 668 and 14,250 according to capsule size. Hatching time varied between 69 and 128 days at 13.5° to 14.5°C.     

Seasonal changes in biochemical composition of the bivalve Astarte montagui in the Clyde Sea Area

Changes in tissue weight and in biochemical composition for a standard animal of the bivalve Astarte montagui (Dillwyn) from a station in the Largs Channel in the Clyde Sea Area were studied during 1969–1971. Spawning took place during the autumn months and was accompanied by a decrease in tissue weight which was then continued until March. Tissue weight increased between April and July. A. elliptica (Brown) and A. sulcata (da Costa) from the same area both showed an essentially similar cycle of tissue weight changes, with evidence that spawning occurred during the autumn. The biochemical changes accompanying this cycle, and the resultant changes in caloric content of the tissues are described for A. montagui.     

Seasonal changes in biochemical composition of the bivalve Chlamys septemradiata from the Clyde Sea Area

Seasonal changes in the tissue weight and biochemical composition of the pectinid bivalve Chlamys septemradiata (Müller) from a station in the Cumbrae Deep, Clyde Sea Area (UK), were studied during 1969–1971. Separate analyses were made of three divisions of the tissues: the adductor muscle, the gonad, and the remaining tissues referred to as mantle. The composition of each of these divisions, and of the total tissues of an animal of standard size was calculated for each sampling date to give information on seasonal changes independent of shell growth. Increase in gonad weight took place mainly between March and May, although there was a slow increase during the winter months (November-March). Spawning in July and August resulted in a fall in gonad weight to very low levels in September and October. The female gonad contained a greater proportion of lipid than the male, and the male a greater proportion of nitrogen than the female, although the total calorific content was similar in both sexes. The adductor muscle showed a clear seasonal cycle of tissue weight and composition, and it was demonstrated that the adductor muscle tissues are a site for storage of reserves. The weight of the adductor muscle was maximal in October-November, and declined through the winter to reach minimum values in March. There was a steady increase during the summer. Lipid, carbohydrate and protein all contributed to the decrease in winter, in part contributing to gonad differentiation but mainly meeting the bivalve's metabolic maintenance requirements. The remaining tissues displayed some irregular fluctuations, but in general the changes showed an upward trend in weight until November followed by a general downward trend to March. The changes are compared with those for other bivalves from the same area.     

Seasonal changes in biochemical composition of the bivalve Abra alba from the Clyde Sea Area

Seasonal changes in the body weight and composition of Abra alba (W. Wood) from south of the Little Cumbrae in the Clyde Sea Area (UK) were studied during 1969–1971. The composition of a specimen of standard size was calculated for each sampling data to provide information on seasonal changes independent of shell growth. Increase in body weight took place rapidly in early summer as the gonad developed and reserves were built up. Spawning in July resulted in a fall in body weight, and this was followed by a slower fall during the autumn and winter as reserves were utilized. The changes are related to seasonal fluctuations in food availability and temperature, which are reflected in the amount of pigment (phaeophytin) retained in the tissues.     

Seasonal changes in biochemical composition of the bivalve Lima hians from the Clyde Sea Area

Seasonal changes in the tissue weight and biochemical composition of the bivalve Lima hians (Gmelin) from a station in the Skelmorlie Bank, Clyde Sea Area, were studied during 1969–1971. The composition of an animal of standard size was calculated for each sampling date to give information on seasonal changes independent of shell growth. Increases in tissue weight took place between April and July as the gonad developed and reserves were built up. Between July and March tissue weight fell, at first rapidly as a result of spawning in the population, and later more slowly as reserves were utilized. Differentiation of the gonad began during the winter, at the expense of stored reserves, but was greatly accelerated during the spring due to increased food from the plankton. The lipid and nitrogen content of a standard animal rose to a pre-spawning maximum in July and then fell. Carbohydrate content also rose during this period, but continued to rise to reach maximum values in September. Carbohydrate and nitrogen both declined during the winter, but there was little indication of any net utilization of lipid during the winter months. The tissues of the ripe female contained more lipid than the male, and the tissues of the ripe male contained more nitrogen than those of the female. The total calorific content of the tissues of the male was greater than that of the female.     

Seasonal and tidal changes in the length of the crystalline style intertidally living Macoma balthica (Mollusca,Bivalvia)

Samples of Macoma balthica were collected during 1978 and 1979 from the westernmost part of the Dutch Wadden Sea. The length of the crystalline style in the stomach of this intertidal bivalve was studied through tidal and annual cycles. The length of the style was ca. half the shell length and changed slightly with the season. Maximum lengths were recorded in spring, the season of high food intake, and minimal values in autumn and winter. Changes in the length of the style also exhibited a tidal cycle, but with two maxima and two minima. Tidal fluctuations in style length amounted to ca. 5% only. The influence of enzymes and waste products from the digestive diverticula, the food intake as well as the influence of the pH on the length of the style are discussed.Communication No. 401 of the Delta Institute     

Chemical defense and evolutionary trends in biosynthetic capacity among dorid nudibranchs (Mollusca: Gastropoda: Opisthobranchia)

Summary. An evolutionary scenario incorporating recent advances in phylogenetic research begins with an opisthobranch-pulmonate common ancestor that was herbivorous and had some diet-derived chemical defense. The Nudibranchia and their closest relatives, the Notaspidea, form a lineage the ancestors of which had switched to feeding upon sponges and deriving protection from metabolites contained in them. Subsequently there have been repeated shifts in food and defensive metabolites, and trends are evident in the ability to detoxify, sequester and utilize metabolites from food, as well as to synthesize defensive compounds de novo. The Notaspidea display a minor adaptive radiation that foreshadows a more extensive one in the various lineages of nudibranchs. This review emphasizes changes that have occurred within the Holohepatica, or dorid nudibranchs (order Doridacea). Their sister-group, the Cladohepatica, consists of three other orders, Dendronotacea, Arminacea, and Aeolidiacea, in which there has been a shift from sponges to Cnidaria as food. The Dendronotacea often feed upon Octocorallia, which combine spicules, chemical defense, and stinging capsules and thereby suggest a transition from feeding on sponges. A previous diet of Octocorallia is suggested by the defensive use of prostaglandins in the dendronotacean Tethys fimbria, which eats crustaceans. A shift to bryozoans in some Arminacea is accompanied by use of different metabolites. Dorid nudibranchs evidently began as sponge-feeders, but some lineages have shifted to a variety of other food organisms, and others have specialized in the kind of sponges they feed on and how they do it. There have been shifts to bryozoans (Ectoprocta) and ascidians (Chordata: Urochordata) that track metabolites rather than the taxonomy of the food. There is a crude correlation between the genealogy and the defensive metabolites of the sponge-feeding dorids. De novo synthesis is well documented in this order and the metabolites are appropriately positioned so as to have an adaptive effect. The hypothesis that the capacity for de novo synthesis was acquired by gene transfer across lineages is rejected, partly on the basis of different chirality of metabolites in the nudibranchs and their food organisms. Instead it is proposed that there has been a preadaptive phase followed by evolution in a retrosynthetic mode, with selection favoring enzymes that enhance the yield of end products that are already present in the food. Received 5 February 1999; accepted 26 July 1999     

Evolution and systematics in Haliotidae (Mollusca: Gastropoda): inferences from DNA sequences of sperm lysin

Abalone taxonomy and systematics have remained unresolved: neither stable species-level nomenclature nor a cladistic hypothesis of relationships among species have been established. To infer the phylogeny of the genus Haliotis and to identify species using molecular data, we compared complementary DNA (cDNA) sequences of sperm lysin from 27 species-group taxa from California, Japan, Australia, New Zealand, Taiwan, Borneo, Madagascar, South Africa, Greece, France, Italy and the Azores. The lysin cDNA sequences reveal that 22 of the 27 taxa are clearly distinguishable by >20 nucleotide differences. Of the remaining 5, H. coccinea from the Azores may be a subspecies of H. tuberculata, if not a sibling species (10 nucleotide differences). The other four taxa are most probably the same species as one of the 22 taxa: the lysin sequences are almost identical between H. madaka and H. discus hannai, H. conicopora and H. rubra, H. diversicolor supertexta and H. diversicolor aquatilis, and H. tuberculata lamellosa and H. tuberculata tuberculata. The phylogeny of lysin cDNA suggests that there are three groups among the 27 species-group taxa: (1) all California species and 3 Japanese species (H. gigantea, H. discus hannai, and H. madaka): (2) 1 New Zealand species (H. iris); (3) 1 Japanese species (H. diversicolor aquatilis), Indo-West Pacific species and European species. These groups can be assigned to three previously recognized subgenera (Nordotis, Paua and Padollus) in the genus Haliotis. Two historical hypotheses are proposed to explain the biogeography and evolution within these abalone: (1) Tethyan distribution of the ancestral abalone, during the Cretaceous, followed by extinction in most of the habitat, but radiation in California and Southeast Asia which later spread to the other areas; (2) North Pacific rim distribution of the ancestral abalone, followed by dispersal to the other areas during the Paleogene.     

Seasonal variations in condition,reproductive activity and biochemical composition of the flat oyster,Ostrea edulis,from San Cibran (Galicia,Spain)

The influence of environmental parameters (temperature, salinity and available food) on the condition, reproductive activity and biochemical composition of a native population of Ostrea edulis L. in San Cibran (Galicia, Spain) was studied between September 1988 and December 1989. Histological preparations of gonads showed that gametogenesis started when temperature was at its lowest in winter. The water temperature in San Cibran never fell low enough to interrupt it. Gametogenesis proceeded slowly and spawning took place in May–June, although the predicted time of ripening was early March. Salinity in San Cibran was relatively stable throughout the year; it did not seem to have any influence on gametogenesis. Available food appeared to be a very important factor in controlling gonad growth, once gametogenesis was initiated. The major concentration of suspended organic particulate matter was present in the spring at the time of rapid gonadal maturation. Only one spawning period was observed. Larvae were released when the food in the water was high. Seasonal changes in the main biochemical components of this oyster were determined for a standard individual. Lipids and carbohydrates presented a similar time-course whereas proteins were constant. When food was abundant, energy reserves were built up. Spawning produced a decrease in biochemical constituent levels, and recovery coincided with the phytoplankton bloom. The stored reserves, mainly lipids, were used to overcome a state of energy imbalance in late autumn associated with low food availability. Results show this oyster to be an opportunist organism which concentrates its reproductive effort during a short period of favourable conditions and which is directly dependent on nutritive availability in the environment.