Volume 46

NEWS

Winkle grazing exacerbates salt marshes die-off

Salt marshes along 1500 km of SE and gulf coastlines of the U.S. have suffered unprecedented die-off in the last six years, primarily as a result of drought. However, there is strong evidence that periwinkles damage live Spartina while grazing their fungal food, facilitating further fungal infection. Surveys of marsh die-off areas revealed high density fronts of Littorina irrorata at the edges. Exclusion experiments demonstrated that the winkles converted the marshes to bare mud flats, and after initial die back, the snail fronts propagated through healthy marsh leading to cascading vegetation loss.

Silliman BR et al. (2005) Drought, snails and large-scale die-off of southern U.S. salt marshes. Science, 310, 1803-1806.

First live giant squid photos

Tsunemi Kubodera from the National Science Museum in Tokyo records (in 28 September 2005 issue of Proc. Roy. Soc. London B) photographs of a giant squid as it grabbed a lure baited with common squid and shrimp pulp attached to a cable beneath a camera, light and depth meter. The squid appeared at 900 metres, wrapped the feeding tentacles into a ball to bring the lure to its mouth, then ascended to 600 metres, before descending again. After 4 h, one tentacle snagged on a hook, was severed and recovered.

http://news.nationalgeographic.com/news/2005/09/0927_050927_giant_squid.html

Snail eyes: when phylogeny meets ecology

Two papers in Invertebrate Biology describe the ultrastructure of the eyes of several land and freshwater pulmonates. Although focal length is fixed, species like Lymnaea stagnalis have eyes adapted by retinal pits to see above and below water. Shallow water species have type I and II photoreceptors, probably specialised for dim and bright light vision respectively, while deeper water species possess only type I receptors.

Bobkova M.V. et al. 2004. Invert. Biol. 123 (2), 101-115.

Gál J et al. 2004. Invert Biol. 123(2), 116-127.

Shellfish, Water Quality and Public Health

Two papers in the Swedish environmental journal Ambio look at reduction of eutrophication in coastal waters by cultivation of Mytilus edulis, and at the need for better risk management with the expansion of aquaculture to minimize the effects of algal toxins like diarrheic shellfish disease and human pathogens transmitted through eating raw or only lightly cooked bivalves. The control strategies include site selection, monitoring of algae, bacteria and viruses, improved indicators of faecal contamination, and rapid dissemination of information. Current mussel farming in a Swedish fjord produces a 20% removal of N and this could be much higher if incentives were offered to increase aquaculture.

Lindahl O et al. (2005) Improving marine water quality by mussel farming: a profitable solution for Swedish society. Ambio, 34(2), 131-138.

Rehnstam-Holm A and Hernroth B. (2005) Shellfish and Public Health: a Swedish perspective. Ambio, 34(2), 139-144.

Personal profiling of Conus venoms

An American team has succeeded in milking venom from two species of fish-eating cone snails (Conus striatus and C. catus) by persuading them to discharge their harpoons into tubes covered by a fish fin. Analysis of the tiny amounts of the cocktail of peptides released by individual snails revealed consistent differences between individuals. Yet, surpisingly, these mixes are a simpler subset of the venoms present in the venom ducts, which are similar between individuals, implying the existence of regulatory mechanisms to select specific venom peptides.

Jakubowski JA et al. (205) Intraspecific variation of venom imjected by fish-hunting Conus snails. J. Exp. Biol. 208, 2873-2883.

Active chemical defenses of sea hares

Sea hares produce distasteful passive chemical defenses in the skin, and also release active chemical defenses when attacked by simultaneous secretions of a bright purple ink from the ink sac and a viscous white substance, opaline, from the opaline gland. The L-amino acid oxidases Escapin (from Aplysia californica) and dactylomelin-P (from A. dactylomela), which also have antimicrobial activity, are secreted along with their substrates L-lysine and L-arginine. Escapin is sequesterd in the amber vesicles, not the red-purple ones which contain algal-derived pigment that gives the ink its colour. Lysine is present in opaline at much higher concentrations than in ink.

Johnson PM et al. (2006) Packaging of chemicals in the defensive secretory glands of the sea hare Aplysia californica. J. Exp. Biol. 209, 78-88.

Can chirality promote speciation in snails?

Left-right asymmetry in snails makes mating difficult or impossible, so have changes in chirality promoted speciation? Molluscan asymmetry is determined by the effects of a maternal 'chirality' gene or genes on the developing embryo- so the individual's phenotype may not correspond to its genotype. In the Japanese land snail Euhadra, mitochondrial DNA phylogeny suggests that there was a single relatively ancient evolution of sinistral species, with more recent single gene speciation or gene flow between chiral morphs that are unable to mate. A mathematical model suggests that speciation by chiral reversal also involves biogeographic factors. Chiral variation can arise by substantial gene flow between morphs because of the maternal inheritance, or there can be reproductive isolation but with gene flow if intra-chiral matings occasionally produce offspring of opposite chirality.

Davison A et al. (2005) Speciation and gene flow between snails of opposite chirality. PLoS Biology, 3(9), e282.

Evidence of sperm trading in a sea slug

Sperm trading is a mating strategy that enforces reciprocity because sperm donation is conditional on sperm receipt. Sperm trading is thought to be widespread in hermaphrodites, and a team in Tübingen has now demonstrated this in the sea slug Chelidonura hirundinina. This species, like other cephalaspids, conveys sperm from the genital aperture to the penis along an open groove. Cauterising the groove interrupts semen flow, producing an experimental 'cheat' that accepts sperm but does not donate it. Other specimens were cauterised on the mantle fold nearby, so they passed sperm normally. These 'sham-treated' specimens donated fewer intromissions to 'cheating' partners than to other 'sham-treated' individuals.

Anthes N et al. (2005) Gender trading in a hermaphrodite. Curr. Biol. 15(19), R792.

Flying snails?

Molecular phylogeny of the clausiliid land snail genus Balea reveals an incredible trans-equatorial journey of 9000 km from Europe to the Azores and the Tristan da Cunha islands - and back! Balea's very sticky mucus, arboreal habit and ovoviviparous hermaphroditism could aid passive dispersal by birds.

Gittenberger E, Groenenberg DSJ, Kokshoorn B and Preece RC. 2005. Molecular trails of hitchhiking snails. Nature 439, 409.

 

 

Etching from the 1567 fable 'Pride comes before a fall' by Marcus Gheeraerts.

Human allergy to snail meat

Snails are a popular delicacy in Europe, but eating snails can induce strong asthmatic or occasionally anaphylactic responses. A study of 60 allergic outpatients with specific IgE to Helix aspersa showed that asthma started 15 min to 3 h after eating the snails. In most cases of snail allergy, house dust mites, Dermatophagoides pteronyssinus, appeared to be the sensitising agent, but snails may also be able to induce sensitisation by themselves. The two major allergens are probably the heavy chains of Helix myosin.

Martins LML et al. (2005) The Helix aspersa (Brown Garden Snail) Allergen Repertoire. Int. Arch. Allergy Immunol 136, 7-15.

A universal open-access web-register for animal names?

ICZN has initiated a 1 year period of consultation on its website at www.iczn.org on the merits of mandatory registration and creation of ZooBank, to be completed by 2008, the 250th anniversary of Linnaeus' animal nomenclature.

Polaszek A. 2005. A universal register for animal names. Nature, 437, 477.

DNA bar-coding tested on cowries

It is claimed that DNA bar-coding, the use of a short fragment of DNA, can identify known taxa and discover new species quickly, objectively and efficiently. When tested on cowries, a diverse group which is well described both morphologically and genetically, over 96% of specimens were correctly identified from a short segment of mitochondrial DNA. However, the possibility of error was higher in 'younger' species. For less well described groups, the failure rate in discovering new species could be 20%.

Meyer CP and Paulay G (2005) DNA Barcoding: error rates based on comprehensive sampling. PLoS Biology 3(12): e422.

Slugs increase grassland diversity, given time

Arion lusitanicus, like other slugs, is a generalist herbivore but with dietary preferences. In a Swiss study of newly established rygrass and clover, species richness and diversity was lower in slug-infested plots in the first two years, but by the third year, richness increased as a result of lowered productivity holding back more competitive species of plants.

Buschmann H et al. 2005. Functional Ecology 19, 291-8.

Growth rings on pulmonate statolith

Embedding statoliths of Nassarius reticulatus in epoxy resin and grinding and polishing reveals growth rings useful in determining age. Would this work with slugs?

Barroso CM et al. 2005. Marine Biol. 146, 1139-44.

Biomimicry of nacreous shell layer

The mechanical properties of mollusc shells and sponge spicules and attempts to mimic the structure with synthetic composites feature in a recent review in Science.

Mayer G. 2005. Science, 310 (5751), 1144-7.

Snail-eating caterpillars of Hawaii

The small, case-bearing caterpillars of one species of cosmopterigid moth, Hyposmocoma molluscivora, do not eat foliage, but prey on the native snail genus Tornatellides. The shell is bound to a leaf by silk restraints before the larva lodges its case next to or within the shell and stretches from the case to reach the retreating body of the snail. Hyposmocoma is an endemic Hawaiian genus, with diverse specializations. H. molluscivora is found on Maui, but an undescribed species of snail-eating caterpillar has been reported from Molokai.

Rubinoff D and Haines WP. (2005) Web-spinning caterpillar stalks snails. Science, 309, 575.

Conus website feeding videos

The Conus Biodiversity website

Http://biology.burke.washington.edu/conus/

in addition to 650 images and 260 PDFs of original species descriptions now has several short videos of envenomation and swallowing of prey by worm-, mollusc- and fish- feeding cones.