The Opisthobranchia comprise a group of highly specialized gastropods with uncertain systematic affinities. Moreover, monophyly of the whole clade has been repeatedly questioned. The present study presents the currently most extensive analyses on opisthobranch phylogeny including 58 species from all major subgroups. A combination of four gene markers as well as diverse molecular systematic analytical approaches are applied in order to shed new light on the evolution of this taxon. Special emphasis is given to the reconstruction of ancestral diet preferences since extant Opisthobranchia feed on a variety of different food items and the development of dietary specialization is supposed to be important for the evolution of these enigmatic marine gastropods. Based on the presented data monophyly of Opisthobranchia is clearly rejected. However, monophyly of the Euthyneura (comprising Opisthobranchia and Pulmonata) is supported. Furthermore, monophyly of most subgroups is revealed. The Runcinacea are found as a separate clade clustering apart from the remaining Cephalaspidea, the taxon in which they have been formerly classified. Furthermore, Aplysiomorpha and Pteropoda are recovered as a monophyletic clade, while the Aplysiomorpha are found to be paraphyletic due to the position of a single taxon. In addition, Cylindrobullida are revealed as part of the sacoglossan subclade Oxynoacea denying their current separate status. The enigmatic Acochlidiacea are revealed as sister group to Eupulmonata. Ancestral diet preferences are reconstructed for monophyletic Euthyneura and all main subclades since polyphyly of Opisthobranchia impeded reconstruction for this clade. Herbivory is found as the most likely ancestral diet of Euthyneura while carnivory probably evolved several times independently in different clades. (1) Institute for Ecology, Evolution and Diversity, GoetheUniversity Frankfurt, Siesmayerstrasse 70, 60054 Frankfurt am Main, Germany e-mail: katrin.goebbeler@ucdenver.edu *Current address: Department of Integrative Biology, University of Colorado Denver, P.O. Box 173364, Denver, CO 80217, USA Thalassas, 27 (2): 121-154 An International Journal of Marine Sciences key words: character evolution, BayesTraits, molecular systematics, diet, herbivory, Euthyneura KATRIN GÖBBELER(1,*) & ANNETTE KLUSSMANN-KOLB(1)

Molecular phylogeny of the Euthyneura (Mollusca, Gastropoda) with spacial focus on Opisthobranchia as a framework for reconstruction of evolution of diet

Snail control is one of the most important tools in the campaign to reduce the incidence of fascioliasis. In order to attain this objective, the method of bait formulation in order to contain an attractant and a molluscicide is an expedient approach to lure the target snail population to the molluscicide. This study identifies certain carbohydrates, namely sucrose, maltose, glucose, fructose and starch, for preparing such baits. These were tested on Lymnaea acuminata, an intermediate host of the digenean trematodes Fasciola hepatica and Fasciola gigantica. The behavioural responses of snails to these carbohydrates were examined. Significant variations in behavioural responses were observed in the snail even when the five carbohydrates were used in low concentrations in snail-attractant pellets. Starch emerged as the strongest attractant for Lymnaea acuminata, followed by maltose.

Behavioural responses of the snail Lymnaea acuminata to carbohydrates in snail-attractant pellets.

Gastropod diversity is substantial in marine and freshwater habitats, and many aquatic slugs and snails use olfactory cues to guide their navigation behaviour. Examples include finding prey or avoiding predators based on kairomones, or finding potential mates using pheromones. Here, I review the diversity of navigational behaviours studied across the major aquatic taxa of gastropods. I then synthesize evidence for the different theoretical navigation strategies the animals may use. It is likely that gastropods regularly use either chemotaxis or odour-gated rheotaxis (or both) during olfactory-based navigation. Finally, I collate the patchwork of research conducted on relevant proximate mechanisms that could produce navigation behaviours. Although the tractability of several gastropod species for neurophysiological experimentation has generated some valuable insight into how turning behaviour is triggered by contact chemoreception, there remain many substantial gaps in our understanding for how navigation relative to more distant odour sources is controlled in gastropods. These gaps include little information on the chemoreceptors and mechanoreceptors (for detecting flow) found in the peripheral nervous system and the central (or peripheral) processing circuits that integrate that sensory input. In contrast, past studies do provide information on motor neurons that control the effectors that produce crawling (both forward locomotion and turning). Thus, there is plenty of scope for further research on olfactory-based navigation, exploiting the tractability of gastropods for neuroethology to better understand how the nervous system processes chemosensory input to generate movement towards or away from distant odour sources.

Olfactory navigation in aquatic gastropods.

Adult Lymnaea acuminata (average length 20-22 mm) were collected locally from lakes and low-lying submerged fields from Gorakhpur. The chemoattraction studies were made in round glass aquaria measuring 30 cm in diameter and filled to a depth of 10 mm with 500 ml dechlorinated tap water. Each aquarium was divided into four concentric zones. At the starting time of the assay 10 snails were placed on the circumference of outermost zone 0. Snail attractant pellets (SAP) were added simultaneously in the center of central zone 3. SAP of different amino acids were prepared at concentrations of 10, 20, 50, 80 and 100 mM/2% agar solution and, subsequently, spread to a uniform thickness of 5 mm. After cooling, SAP were cut in small pieces of 5 mm in diameter. Lymnaea acuminata's attraction to amino acids was studied using different amino acid concentrations in SAP. Pellets containing amino acids with non-polar R groups (proline and tryptophan), a charged polar group (arginine) and uncharged polar R groups (serine, citrulline and asparagine) were tested. The snails were more attracted to the uncharged polar R group amino acid serine than to other groups of amino acids. The preferred amino acid concentration was 80 mM. The attraction of snails to different amino acids was concentration dependent. Snails could discriminate amongst the different amino acids at > or = 50 mM.

/pdf/attraction-to-amino-acids-by-lymnaea-acuminata-the-snail-2m5qwo1gxo.pdf

Attraction to amino acids by Lymnaea acuminata, the snail host of Fasciola species

Aim: Fascioliasis is an impor- tant helminth disease caused by Fasciola (F.) he- patica and F. gigantica of Asia and Africa. This disease belongs to the plant-borne trematode zoonoses. Human infection has been reported in 51 different countries from 5 continents. One of the possible approaches to control this problem is to interrupt the life cycle of the parasitic trematodes by eliminating the snail. Materials and Methods: Snails attractant pellets (SAP) were prepared from binary combi- nation of carbohydrate + amino acid (20 mM) in 2% agar solution with active molluscicidal com- ponent Ferula asafoetida (ferulic acid, umbellif- erone), Syzygium aromaticum (eugenol), Carum carvi (limonene). Attraction of snails to different combinations was studied by using clear glass aquaria having diameter of 30 cm. Each aquari- um was divided into four concentric zones; zone-3 (central zone), zone-2 and zone-1 (mid- dle zone) and zone-0 (outer zone) had a diame- ter of 13, 18, 24, and 30 cm, respectively. The behavioral responses of snails to these binary combinations of carbohydrate and amino acid in bait formulation were examined. The fraction of snails that was in contact with the SAP at different times was used as a measure of at- traction. Results: Among all the binary combination of carbohydrate+amino acid+molluscicide after 2h of experiment, highest attraction of snail (54.71%) was observed towards the SAP con- taining starch+histidine+limolene. Limonene+ starch+histidine containing SAP emerged as the strongest bait formulation (96h LC50 0.74%) against Lymnaea acuminata. Conclusions: The present study suggested that the molluscicides of plant origin could be used with varying degrees of success in bait for- mulation.

/pdf/combination-of-molluscicides-with-attractant-carbohydrates-48uhnkze6c.pdf

Combination of molluscicides with attractant carbohydrates and amino acids in bait formulation against the snail Lymnaea acuminata.

1. Helisoma duryi, a planorbid snail has been suggested as a biological control agent against the snail intermediate hosts of schistosomes, Biomphalaria and Bulinus species. It has been demonstrated that competition for food resources is involved. The aim of this paper is to compare the ability of these species to locate food sources. 2. The paper compares the accumulation of groups of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus on varying amounts of two different artificial food preparations and the movement of individual snails of these three species when approaching a food source by analysing their tracks. 3. There were slight differences in the ability of H. duryi and B. camerunensis to locate food preparations, but both were superior to B. truncatus. The two types of food preparations differed markedly in their attraction of B. truncatus. H. duryi was less attracted to the food preparations with the two lowest amounts of food of both types than to preparations with larger amounts of food, while this was not observed for B. camerunensis and B. truncatus. Medium-sized H. duryi were superior to small and large snails in their ability to locate food, while no significant differences were found among three size groups of B. truncatus. 4. Analysis of snail tracks did not reveal an increased frequency of turning in any of the three species as the food source was approached. The reason for the higher accumulation of H. duryi and B. camerunensis on the food could in part be explained by their higher activity level. Other explanations are also discussed.

H. Madsen

Papers

A comparative study on the food-locating ability of Helisoma duryi, Biomphalaria camerunensis and Bulinus truncatus (Pulmonata : Planorbidae)