Trail following in the chiton Acanthopleura gemmata: operational and ecological problems

The Indo-Pacific, intertidal chiton Acanthopleura gemmata (Blainville) is a central place forager which occupies definite, actively dug and defended scars, and migrates during nocturnal low tides up to 3 m away to feed on algal grounds. After each feeding excursion, most chitons home precisely to their scars. Photographic tracking, using lightemitting diodes (LED) glued to the chitons, and experiments were conducted throughout 45 d (August to September 1984) along the Nimu Peninsula (Somalia) in order to elucidate the importance of trail following in the homing and feeding of this species. LED tracking of the chitons throughout each activity phase and trail interruption experiments showed that following the personal outgoing trail is a basic homing mechanism in this species. Translocation of the chitons on a conspecific trail and homing performance analysis revealed that the trail-associated information involved in the homing is polymorphic in the population, thus minimizing the probability of following a conspecific trail despite the frequent trail crossings due to high population density. The LED tracking throughout successive activity phases showed a high coincidence between the paths traced by the same chiton night after night. In the few cases when the outgoing and return paths of the first night markedly diverge, the home-feeding ground route of the successive night overlaps the return trail of the previous night. A less pronounced inter-individual trail following also occurs during foodward excursions. These findings suggest that the trails released by A. gemmata are complex, including both quasi-individual and species-specific information. Moreover, this chiton may utilize its trail following capacity not only to home, but also for the retrieval of the feeding grounds night after night.     

Seasonal changes in the biochemical composition of the chiton Chiton iatricus (Polyplacophora: Mollusca) and the marine pulmonate Onchidium verruculatum (Gastropoda: Mollusca) in relation to their reproductive cycles

Seasonal changes in the biochemical composition of two molluses, gonochoric Chiton iatricus and a marine pulmonate, Ochnidium verruculatum inhabiting the same tropical area, but having different modes of reproduction, were studied. Protein is the major biochemical component stored in C. iatricus, whereas lipid is predominantly stored in O. verruculatum. The correlation between these quantifications and the annual reproductive cycles of the two species investigated suggest that nutrients stored in the somatic body parts are channeled towards the gonad during the gametogenesis. In C. iatricus sexual differences efrist in the biochemical needs of the ovary and the testis. The ovary always has a higher protein content than the testis. In the hermaphrodite pulmonate O. verruculatum, biochemical expenditure on gamete production is relatively low because this species has to spend energy on the reproductive propagation viz. copulation and egg-laying. On the contrary, in C. iatricus the biochemical energy is mainly utilized for the production of gametes which have to be produced in great numbers in order to counter-balance the loss of gametes caused by external fertilization. The collected data are discussed in the light of comparative physiology of reproduction.     

Growth and population structure of Lepidochitona cinereus (Mollusca: Polyplacophora) infected with Minchinia chitonis (Protozoa: Sporozoa) at Easthaven,Scotland

Growth and population structure of Lepidochitona cinereus was studied at Easthaven in Scotland. Length was isometrically related to height and breadth, while tissue dry weight was negatively allometric. Length-shell weight relationships were variable with the time of year. Periods of differential growth were associated with the onset of growth in spring and gonad development in July. The use of growth-check lines to age individuals is described. Population structure and growth was investigated using a combination of winter growth-check line and length-frequency analyses. Infection with the protozoan Minchinia chitonis is shown to cause enhanced growth and deviation from the normal growth curve. Individuals survived for a maximum of 5 winters and length-frequency data could be interpreted only after growth-check line analysis due to extensive overlap of year-class size ranges. Year-class success was variable, and the present population was dominated by older year-classes.     

Swimming behaviour of the saucer scallop Amusium balloti (Mollusca: Pectinidae)

The swimming performance of the saucer scallop Amusium balloti (Bernardi) was recorded from tests conducted in a natural environment in Shark Bay, Western Australia, in June, July and November 1984 and June and September 1985. Unlike all other scallops described in the literature, the swimming performance (both speed and distance) of A. balloti increases with size. Maximum distance swum in a single swimming event was 23.1 m, while the maximum cumulative distance swum (four swimming events) was 30.8 m. Swimming speeds for larger scallops were generally between 0.8 and 1.0 m s^-1 (1.6 and 2.0 knots), with a maximum speed of 1.6 m s^-1 (3.1 knots). Variations in swimming performance and response times with size and season are probably the major cause of variations in the scallop's vulnerability to fishing gear.     

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.     

Competition and interaction between Neosarmatium smithi (Crustacea: Grapsidae) and Terebralia palustris (Mollusca: Gastropoda) in a Kenyan mangrove

 In a Kenyan mangrove, we studied the interactions between the gastropod Terebralia palustris and the crab Neosarmatium smithi when foraging on decaying mangrove leaves. Interactions are considerable on account of their wide overlap in zonation (Rhizophora mucronata belt), food items (mangrove leaves) and activity window (diurnal low water). The snails find a leaf by a systematic transecting of the platform and eat the leaf after crawling on to it, usually en masse. The crabs rarely venture beyond 80 cm from their burrows, and once they find a leaf they quickly drag it back into their burrow, probably to reduce the strong intra-specific competition. A crab is able to drag a leaf away even if a number of snails are already feeding on it, by strongly pulling the leaf away or by pushing the snails off the leaf. The success of the “thief ” depends on both the crab's size and the number of snails on the leaf. Received: 25 July 1999 / Accepted: 27 April 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.     

Bacterial associations in the teredo Bankia australis (Lamellibranchia: Mollusca)

Electron microscope examination of the so-called Gland of Deshayes in the teredos Bankia australis and related species has revealed that this structure is not a glandular tissue, but represents associations of bacteria.     

Functional and environmental anaerobiosis in the razor-clam Ensis directus (Mollusca: Bivalvia)

In Ensis directus (Conrad) metabolic changes accompanying muscular activity and experimental anoxia were investigated. Octopine dehydrogenase, strombine dehydrogenase, alanopine dehydrogenase and lactic dehydrogenase were shown to be present in different parts of the body, but the activity of ODH always exceeded that of the other enzymes by far. Muscular activity connected with escape digging or evoked by electrical stimulation resulted in a decrease of stored phosphagen and in an accumulation of octopine. During recovery the normal concentrations of energy-rich phosphates were restored quickly, whereas octopine was removed more slowly. In experimental anoxia only minor quantities of L-and D-alanine, succinate, propionate, and acetate were formed. Quantitatively the most important endproduct was strombine, which rose linearly with the duration of anoxic incubation.     

Laboratory rearing of Sepiolinae (Mollusca: Cephalopoda)

Five species of Sepiola and Sepictta were reared in the laboratory from egg to adult size. Spawning was achieved in 3 species of Sepiola after 5 to 7 months. The growth rate of the species reared did not depend upon temperature, which ranged from 12.5° to 20°C. A fairly constant size increase (2.5 mm mantle length/month) was observed in Sepiola during the 5 months after hatching. In Sepietta, the same growth rate was observed until the fourth month after hatching, when it increased to the rate of 5 mm mantle length/month.Laboratoire associé au C.N.R.S.     

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     

Advanced age for sexual maturity in the ocean quahog Arctica islandica (Mollusca: Bivalvia)

A study of gonadal state in 39 small specimens of Arctica islandica Linné collected in April 1976 from the Middle Atlantic shelf of North America suggests that sexual maturity is reached at a later age than has been reported for other shelf bivalves. Eight of the specimens had gonads in the undifferentiated state. On the basis of annual internal growth banding in the shells of these immature specimens, age ranged between 4 and 14 years. Average age was 9.38 years (standard deviation, s,= 3.54). Shell length ranged from 24 to 47 mm (average 38.85 mm, s=9.25). Differentiated gonads were found in specimens as young as 6 years. Age of maturity shows a wide range and may be dependent upon growth rate and locality.     

Structural chromosomal polymorphism in the dog-whelk Nucella lapillus (Mollusca: Neogastropoda)

On the English and French Channel coasts, the dog-whelk Nucella lapilus (L.) exhibits variation in chromosome number which appears to correlate with the degree of wave action on the shore. The more common, 2n=26 morph is typically found on exposed shores subjected to a high degree of wave action, whereas those with higher chromosome numbers, up to the recorded maximum of 2n=36, are restricted to more sheltered environments. The polymorphism is thought to be Robertsonian in nature, involving centric (centromere) fission or fusion, but detailed analysis of the polymorphism has been restricted by lack of success in labelling individual chromosomes. Using a silver-staining technique for the nucleolar organiser regions (NORs), three pairs of chromosomes, in the basic 2n=26 karyotype, have been positively identified. A series of structural chromosomal rearrangements (pericentric and paracentric inversions) affecting one pair of chromosomes involved in the numerical polymorphism is described. Significant differences exist between populations with respect to this character. These chromosomal rearrangements have the potential to reduce the level of interbreeding between the different types, and may act as isolating mechamisms between breeding groups. Structural chromosomal polymorphism is likely, therefore, to have greater significance in relation to adaptation than simple numerical variation. This finding raises important questions concerning the (cyto)taxonomic status of N. lapillus in different parts of its range.     

Reproduction and condition of female Octopus mimus (Mollusca: Cephalopoda)

The relationship between reproduction and condition was studied in a 15 mo sample of 919 maturing, mature and post-spawning female Octopus mimus (388 to 3714 g) caught in Iquique (North Chile). O. mimus is a semelparous species, with reproduction taking place all year round. Investment in reproductive tissues was, on average, 9.9% of mature female body weight, independent of season. However, somatic growth during maturation was dependent on season and varied between 26 and 63% of the whole-body growth in weight. The condition of females did not vary markedly until spawning, although seasonal variations were apparent, winter being the most unfavourable. Condition deteriorated dramatically after spawning, during parental care of the eggs. During this period, somatic-tissue depletion, mainly from the muscles, was >25% of the total body weight of mature females. The fecundity of O. mimus was probably limited by the costs associated with parental care of the eggs.     

Adolescent social environment shapes sexual and aggressive behaviour of adult male zebra finches (Taeniopygia guttata)

Adolescence is the pivotal transitional phase during which animals become sexually and socially mature and acquire the skills to cope with a variety of environmental challenges on their own. We investigated in a bird species, the zebra finch, how the social environment experienced during this period influences their behaviour in a sexual context. Zebra finches were kept in pairs (male–female or male–male) or larger mixed-sex groups (three males and three females) during adolescence and the long-term consequences were studied on courtship behaviour, aggressiveness and attractiveness in 42 males. To investigate the stability of the observed effects over time, all behavioural tests were repeated approximately 4 months after the initial recordings. Males that grew up with a single female showed the most intense courtship and highest aggressiveness and were most attractive to females, while group-reared males had the lowest courtship and aggressiveness and were the least attractive. The observed differences in courtship and aggressiveness were stable, while the differences in attractiveness disappeared over time. These findings are very similar to earlier studies on guinea pigs, indicating that the observed effects represent a general phenomenon, not restricted to mammals with a similar function and presumably also similar underlying mechanisms.     

Sperm morphology in the marine gastropodArchitectonica perspectiva (Mollusca): Unique features and systematic relevance

The marine amphipodAllorchestes compressa Dana, fed on the seagrassHeterozostera tasmanica, was exposed to sublethal concentrations of Cd, Cr, Cu and Zn for 4 wk in flowing sea water, and the concentrations producing the minimum detectable decreases (the minimum effect concentrations, MECs) in average weight, survival and biomass (average weight × survival proportion) were estimated by interpolation from regression models. Survival and biomass were more sensitive than average weight as indicators of sublethal effects. The lowest values of MEC for Cd, Cr, Cu and Zn were 11, >250, 3.7 and 99µg 1^–1, respectively. For Cu, this value fell below the minimum risk concentration (MRC) calculated from acute toxicity tests (LC₅₀) and application factors (AF); for Cd, the MEC was similar to the MRC; for Cr and Zn, the MECs were well above the MRCs. The metal concentrations in the amphipods at the MECs were 46, >46, 364 and 139µg g^–1 dry wt for Cd, Cr, Cu and Zn, respectively. Accumulation of the nutrient metals (Cr, Cu and Zn) showed some evidence of metabolic regulation, but the non-nutrient Cd was accumulated without regulation until the amphipods died. In general, those metals that were more highly accumulated by the amphipods were the more toxic.     

Sperm motility and longevity in the giant cuttlefish, Sepia apama (Mollusca: Cephalopoda)

The sperm kinetics and fertilisation literature in marine invertebrates is heavily biased toward free-spawning species. Nonetheless, many species (e.g. cephalopods) transfer and/or fertilise gametes in confined external spaces or internally, creating very different selective pressures on sperm storage, sperm longevity and hence sperm competition. Here we report the results of an investigation into the effects of sperm age, water temperature and sperm concentration on sperm motility in the giant cuttlefish (Sepia apama). Significant positive correlations were found between percent motility and sperm concentration, and between sperm motile speed and sperm concentration. Mean percent motility of cuttlefish sperm suspension was still 9% eight hours after being released from the spermatophore and diluted into filtered seawater at 12°C (ambient field temperature during the spawning season). Sperm resuspended from spermatangia taken from (mated) females in the field were motile for up to 100 hours. When spermatophores were stored at 4°C motility was still observed in resuspended sperm after two months. Our results show that spermatangia and spermatophores can retain and release live sperm for long periods. The observed longevity of sperm in S. apama greatly increases the potential for sperm competition in this species.