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& Saturday, 16-17 April 2004 The Malacological Society of London |
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Behaviour
and Neurophysiology of Molluscs The Society’s two day annual spring meeting attracted nearly 50 participants to the leafy Kingston Hill campus. The conference dinner was an entertaining river cruise down the Thames passing through locks, when meals (fish and chips) were loaded aboard at the gates of Hampton Court. Richard Cook and his team of helpers are to be congratulated for organizing such a successful academic and social event. Abstracts of the 27 presentations follow in alphabetical order of first author. |
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The eyes on the basis of their few retinal elements and fish-eye lens have poor visual acuity and seem designed as light-gathering devices. However, optomotor responses and shock-avoiding conditioning in a choice chamber illustrate some visual acuity. Snails also discriminate between areas of different luminance at low light intensities.
These results question the existence of muscarinic-like receptors in the cuttlefish brain whereas nicotinic-like receptors are largely expressed. Significant decreases in [3H]cytisine binding density were also evidenced in most central regions of old cuttlefish when compared to mature animals. The major decrease (-71%) found in the superior frontal lobe, involved in visual learning, might be related to the previously demonstrated alteration of cholinergic neurons in this lobe during aging. [POSTER PRESENTATION]
1 Université de Caen, France; 2Unité de Psychopathologie Morphologique, Switzerland; 3Université de Bordeaux, France
Slug feeding behaviour and its application to pest control A S Brooks1, M J Crook1, A Wilcox1, R T Cook2 1Harper Adams University College, UK; 2 Kingston University, UK The field slug Deroceras reticulatum (Müller) is the most important slug pest of winter wheat crops in the UK. Despite the widespread use of chemical methods of control, severe damage to the crop can remain a problem. Not only can molluscicides be unreliable, their use also raises environmental concerns. Hence, the provision of an alternative source of food for slug pests as a novel means of slug control may become increasingly viable. In this study, legume species were chosen as the alternative food source. After an initial preference test of 10 species, red clover (Trifolium pretense L), was found to be the most palatable with an Acceptability Index (AI) of 0.81, whilst the lowest AI was 0.42, highlighting the distinct feeding preferences of D. reticulatum. Further laboratory and field based experiments investigated how slug feeding behaviour affected damage to wheat at two different slug populations and red clover densities along with the molluscide metaldehyde. Feeding behaviour was inferred by the absolute amounts of damage to wheat or clover or molluscide eaten. Initial results suggest that slugs were most likely to eat whatever they encountered; independent of food type (after all, wheat is highly palatable in its own right). This revealed that a high density of a palatable alternative food would be required to make this a viable means of effective slug control.
D Brooks, L Collis, T Fort, Y Sun, J Wu & R Hill, University of Rhode Island, USA Molluscan preparations have provided models for the control of behaviour at the levels of central nervous systems, receptor physiology, efferent peripheral nerves, synapses and control of somatic, visceral and cardiac muscle. Buccal feeding muscles and cardiac muscle of a whelk have been used for a study of the molecular properties of neurally released biopeptides. The results have clarified the differing structural requirements for control of the two types of muscle and for inhibitory and excitatory interaction between neuropeptides. The bivalve myocardium is also under extrinsic control, as by neurotransmitters and the tetrapeptide FMRFamide, but behaviouraliy control by autoregulation is significant. Studies of shortening deactivation of ventricular trabeculae of the surf clam indicate that muscle length modulates membrane potential and the extent of calcium activation of myofilaments. Additionally, NO plays a regulatory role for this cGMP-dependent bivalve cardiac muscle. Force of contraction of "cardiac smooth muscle", controlling output of molluscan hearts, is controlled by the time course of the cardiac action potential. At a theoretical level, a computer model has enabled a study of the dependence of the time course of the cardiac action potential on ionic currents.
Neural Controls on the Release of Gametes in Helix aspersa R Chase, McGill University, Canada
Feeding responses to amino acids in an opisthobranch mollusc, Pleurobranchaea japonica S Chiken & K Kuwasawa, Tokyo Metropolitan Institute for Neuroscience & Okayama University of Science, Japan We studied a conditioned reflex in the adult of Pleurobranchaea japonica, a carnivorous opisthobranch collected by fishermen at Tokyo bay and fed with squid and shrimp meat in a laboratory aquarium. They show feeding responses such as orientation and locomotion to the origin of a stimulus, and extrusion of the proboscis at the origin. We found that they also show feeding responses to some simple amino acids, including glycine. We found, on the other hand, light stimuli evoke apparent aversive responses, involving the gill withdrawal reflex. After animals were trained with repetitive paired stimuli of glycine in seawater poured in front of the mouth and light stimuli to the whole dorsal surface of an animal, the animal showed conversely the gill withdrawal response to the glycine conditioned stimulus. Besides the behavioral changes, we confirmed the achievement of a conditioned aversive reflex in intact animals, by recording of motor impulses with implanted electrodes from the branchial nerve. Moreover, we found that this conditioned reflex was kept in an isolated preparation of only the nervous system, and organs related to the reflex. [POSTER PRESENTATION]
The effect of early feeding experience on subsequent prey preference in cuttlefish, Sepia officinalis A-S Darmaillacq, R Chichery, R Poirier and L Dickel, Université de Caen, France We investigated the effect of early feeding experience on subsequent prey preference in juveniles of Sepia officinalis. First, choice tests between 3 prey items were conducted at day 3 in naive juveniles and at days 6, 30, 60 and 90 of post-embryonic development in cuttlefish only fed shrimps, their originally preferred prey. The results show that without any prior experience cuttlefish preferred shrimps at 3 days and throughout the first week of post-embryonic development; this suggests that their choice could be guided by a ‘hard-wired’ program at least during the first week of life. This ‘innate’ preference can however be modified by early individual experience. We indeed induced a preference for the originally least preferred prey (crabs) in naïve cuttlefish. This ‘new’ preference may correspond to some learning processes, involving a form of long-term memory trace of it in 7-day old cuttlefish. This is the first demonstration of the existence of a kind of long-term memory in such young cuttlefish. Last, it appears that after one month, although they have only been fed shrimps so far, i.e. their originally prey preference, cuttlefish have a tendency to switch their preference to novel prey and then to diversify their diet.
Behavioural flexibility and learning in cuttlefish, Sepia officinalis L Dickel, C Alves, C Bellanger, A-S Darmaillacq, N Graindorge, MP Chichery & R Chichery, Université de Caen, France In differently aged cuttlefish, we used an associative learning paradigm with negative reinforcement to estimate the short and long-term memory abilities (STM and LTM) during animal life span. We observed an early post-embryonic maturation of the STM (up to 8 days of age). This phenomenon is confirmed by an increasing prey pursuit ability (involving STM processes) during the first week of life. The LTM progressively increases until 90 days of age, moreover, this maturation process in juveniles is highly dependent of the environment of rearing. Inversely, LTM performance crucially decreases in old animals. These variations of LTM abilities during development are associated with, in one side, the post-embryonic maturation of the vertical lobe complex in juveniles and, on the other side, with the occurrence of signs of degeneration in this highly associative brain structure in aging cuttlefish. We recently confirmed the functional implication of the vertical lobe complex in teaming and memory by the use of a metabolic marker (cytochrome oxidase) in adult animals. Further experiments of excitotoxic lesions of the vertical lobe associated with different learning paradigms are actually leaded in our laboratory.
Control of feeding in Lymnaea by octopamine Christopher J H Elliott1 & Ajgnes Vehovszky2 1 University of York & 2 Balaton Limnological Institute Octopamine was first discovered in cephalopod molluscs, but was mainly seen as having a neuroactive role in arthropods. Over the last 7 years, however, we have shown that octopamine plays an important role in the feeding system of the model gastropod, Lymnaea stagnalis. Neurons in the buccal ganglia are octopamine immunoreactive and make synapses with all the known feeding neurons in the buccal ganglia. Stimulation of the octopamine-containing (OC) interneurons activates fictive feeding in the isolated CMS, or stabilises an existing feeding rhythm. It also reconfigures the pattern. The OC interneuron also has longer, polycyclic actions that maintain feeding, acting through modulation of the strength of synaptic connections and through activation of voltage - sensitive sodium channels. These observations fit with a role for the OC interneuron in strengthening feeding behaviour.
Reviewing the neuroendocrine system that controls reproduction in terrestrial pulmonate gastropods V Flari, Central Science Laboratory, York, UK In this paper we review the current state of knowledge about the endocrine system, its interactions and its putative role in the regulation of reproduction in terrestrial pulmonate gastropods. Within this context, we review the possible endocrinological role of the optic tentacles, the dorsal bodies cells, the gonad, and certain groups of neurosecretory cells. In addition, we discuss the possible chemical nature of some of the hormones that may be involved in regulating reproductive processes in slugs and snails. The fact that most of the research on the reproductive physiology of terrestrial snails and slugs is now somewhat dated, and that many of the questions that emerged during the 70s, 80s and early 90s remain unanswered is emphasized. This review also highlights the continuing general lack of knowledge about the reproductive physiology of terrestrial pulmonate gastropods, by comparison with our understanding of these processes in freshwater representatives of this subclass. This disparity leads us to conclude that more research into the physiology of terrestrial pulmonate gastropods is needed in order to understand these processes in molluscs as a group.
Moving towards perfection? Locomotion of large slugs including the hybrid Arion ater x A. lusitanicus Jan Hagnell 1, Ted von Proschwitz2, Christoffer Schander,3 1 University of Göteborg, Department of Zoology, Box 463, SE-405 30 Göteborg, Sweden. 2 Göteborg Natural History Museum, Box 7283, SE-402 35 Göteborg, Sweden. 3 University of Bergen, Department of Biology, Thormohlensgt. 55, NO-5020 Bergen, Norge Three species of large slugs- Arion ater Linnaeus, 1758, Arion lusitanicus Mabille, 1868 and Limax maximus Linnaeus, 1758, were measured during crawling in the field in South-west Sweden for two consecutive summers. The crawling distances were measured for a fixed time span and recorded with temperature and relative humidity. All of the slugs primarily identified as A. lusitanicus were dissected and individuals determined as being hybrids between A. lusitanicus and A. ater were treated separately. Analysis of the data collected show that there is significant difference in crawling distance between the four groups (the three species + the hybrids) but not between the A. lusitanicus and the hybrids. All slugs crawl longer with higher temperature and lower humidity. When put into relation with each other, the hybrids tend to act like the L. maximus in having its longest crawling distances at low and high temperatures and intermediate humidity. We suggest that the hybrids may have adapted to a temperate climate (behaving like L. maximus) but still have much of the morphological and physiological features of the recently immigrated Iberian slug A. lusitanicus.
Influence of slug behaviour on approaches to control S Hewlett & G Port, University of Newcastle, UK Slugs are major pests of crops and ornamental plants. Control currently relies heavily on the use of molluscicides which can also cause damage to populations of non-target species. It is, therefore, desirable for both environmental and economic reasons to apply such control at times when it is likely to be most effective, rather than prophylactically. Central to achieving this is an understanding of factors that affect the behaviour of the pest species. This poster will provide an overview of some key behavioural characteristics of slugs that influence the success of control programmes and the methods used to study this behaviour. Particular emphasis will be given to the response of slugs to molluscicides pellets and their behaviour in refuge traps used for sampling field populations. [POSTER PRESENTATION]
Characterization of the transmitter (acetylcholine, serotonin, dopamine) receptors in the CMS of the pond snail Lymnaea stagnalis L Hiripi, A Vehovszky, CJH Elliott*, K Elekes, Balaton Limnological Institute, Hungarian Academy of Sciences; *Department of Biology, University of York, UK We characterized acetylcholine (Ach), serotonin (5HT), dopamine (DA) receptors in the Lymnaea brain, with ligand binding method. The following labeled ligands were used: 3H-nicotine, 3H-quinuclidiyil-benzylate (Ach), 3H-5HT, 3H-5-Carboxamidotriptamine, 3H-Ketanserine, 3H-GR6563,3H-LSD (5HT), 3H-spiperon, 3H-SCH23390, 3H-LSD (DA). The ligands of cholinergic receptors bound with high affinity to the membrane preparation of Lymnaea brain. Pharmacological properties of the binding suggest the presence of both nicotinic and muscarinic receptor types. No specific binding of 3H-Ketanserin and 3H-GR6563 could be found, suggesting that the vertebrate 5HT2 and 5HT3 subtypes of serotonin receptors are not present in Lymnaea. The 5HT1 receptor ligands 3H-5HT and 3H-5-Carboxamidotriptamine bound with low affinity, suggesting that the 5HT1 receptor is missing in the CMS. DA1 and DA2 dopamine receptors could not be identified either, because the selective ligands of these receptors bound only with low affinity to the membrane preparation. The 3H-LSD was the single ligand displaying a high affinity binding to both serotonin and dopamine receptors. The results suggest, that the muscarinic and nicotinic cholinergic receptors are conserved throughout the evolution, whereas the serotonin and dopamine receptors of vertebrate type are not characteristic in molluscs. [POSTER PRESENTATION] Supported by OTKA grants, Nos. T34106 and T046580 and the Wellcome Trust.
Investigating the sensory pathways involved in chemical conditioning Julie Ireland, Volko Straub, Michael O’Shea, Paul Benjamin. University of Sussex, UK. Feeding behaviour in the pond snail Lymnaea stagnalis can be conditioned by a single pairing of sucrose, the unconditioned stimulus (US), with amyl acetate, the conditioned stimulus (CS). The resulting associative learning leads to long-term memory formation (Benjamin et al, 2000)1. Current research is concerned with investigating the sensory pathways leading to the activation of feeding and uncovering neural correlates of learning. Detection of the US and CS occurs at two main sensory areas, the lips and the oesophagus. From these external and internal structures arise two anatomically distinct pathways leading to the activation of the feeding central pattern generator (CPG). These pathways are the principle focus of current research, since it is here that learning-related plasticity is likely to occur. Reduced preparations isolating the lip and oesophageal pathways of naive animals demonstrate that the US elicits a neural response, while the CS does not. Also reported here is progress towards localising the memory trace. Intact animals have been conditioned and then learning induced changes at the level of the neuron investigated. The cerebral ganglia, being part of the lip pathway, is implicated as the most likely site for plasticity. 1 Benjamin, P.R., Staras, K. and Kemenes, G. (2000), A systems approach to the cellular analysis of associative learning in the pond snail Lymnaea. Learning and Memory 7: 124-131
Sex role reversal in the simultaneous hermaphroditic pond snail Lymnaea stagnalis is determined by the availability of seminal fluid J Koene & A Ter Maat, Vrije Universiteit, The Netherlands Encounters between potential mating partners are usually accompanied by sexual conflict. In the case of simultaneously hermaphroditic animals that perform one sexual role at the time, this conflict arises over the division of the sexual roles. If both animals prefer to mate only in one role this conflict can be solved by sex role reversal after the first mating, resulting in either egg or sperm trading. Although patterns of apparent sperm trading have been reported in several hermaphroditic species, we here investigate whether this is the only possible explanation for such mating patterns. In the pond snail Lymnaea stagnalis sexual isolation increases male sexual drive, which is regulated via a nervous connection between the prostate gland and the central nervous system. Using sexually isolated and not-isolated individuals we show that only in pairs where both animals were isolated result in sex role reversal. Previous studies have interpreted such results as sperm trading. However, based on our finding we conclude that future experiments aimed at demonstrating sperm trading will have to be designed very carefully, preferentially taking knowledge of the underlying mechanisms into account. [POSTER PRESENTATION]
Inhibition of the serotonergic neuron Anti-L7 is involved in sensitization of the gill withdrawal reflex in Aplysia M Kurokawa & K Kuwasawa, Tokyo Metropolitan University, Japan L7 is a gill motor neuron that drives the gill longitudinal shortening in Aplysia califomica, A. kurodai, and A. juliana. We have identified a neuron in the serotonergic RB cluster of the abdominal ganglion. We referred to the neuron as Anti-L7, which opposes L7-driven longitudinal shortening in these species. Anti-L7 did not block the generation of L7 impulses within the abdominal ganglion, but, rather, it opposed the L7-driven longitudinal shortening of the gill at the periphery. Recordings from RB cluster neurons in in vivo specimens suggested that the spontaneous firing rate of Anti-L7 impulses was less than several Hz. The suppression of the L7-driven longitudinal shortening was dependent on the firing rate of Anti-L7, and, the threshold firing rate of Anti-L7 impulses for these suppressive effects was less than 0.5 Hz. In response to electrical stimuli applied to the pleuro-abdominal connective, impulse firing of Anti-L7 was inhibited even for several minutes after stimulation ceased. During this inhibition, the L7-driven longitudinal shortening of the gill was potentiated. These results suggest that sensitization of the gill withdrawal reflex is, at least in part, attributable to the inhibition of Anti-L7 activity. [POSTER PRESENTATION]
Reproduction or defence: mechanistic explanations for aggregation behaviour in the limpet Patella vulgata L Langaard, H Wood & R Coleman, University of Plymouth, UK Aggregation behaviour by marine and terrestrial molluscs has been observed in almost every biome. The causal basis of this behaviour is not yet understood. In common with many other aggregating animals, aggregation by limpets has been suggested to have costs and benefits. The costs are proposed to be apparency to predators, competition for food and access to grazing. Benefits have been demonstrated in terms of reduced vulnerability to avian predators, but this is a consequence of aggregation. Aggregation behaviour by juvenile limpets can be induced by the provision of shelter by macroalgae, but the factors that cause adult limpets to move to groups is not known. It could be that aggregation by limpets may be increased by animals forming/enlarging groups for reproduction or in response to predation. We used a mixture of manipulative and mensurative field experiments to examine the aggregation response of limpets in response to elevated predation threat and also to see if groups of P. vulgata were more or less synchronous in terms of reproductive state. [POSTER PRESENTATION]
Directionality in the skin display system of squid Sepioteuthis sepoidea J Mather, University of Lethbridge, Canada
Brain maturation and early experience in cuttlefish (Sepia officinalis) R Poirier, R Chichery & L Dickel, University of Caen, France In cephalopods, previous studies have shown the implication of different brain structures in learning and memory. In the present work, we examined in the cuttlefish whether enriched early experience affects neurogenesis in these structures during the first weeks of post-embryonic development. In this aim, we have adapted the bromodeoxyuridine (BrdU) immunohistochemical technique to the cuttlefish. BrdU is a thymidine analog which is incorporated into DMA during the S-phase of the cell cycle. Then, immunodetection of BrdU some hours after injection reveals the cells produced during the integration time of BrdU. Newly hatched and fifteen-day old cuttlefish reared either in impoverished or enriched environment were injected with BrdU. 24 hours after injection, cuttlefish were killed, and BrdU was immunohistochemicaly detected. Densities of BrdU labelled cells in the optic, vertical and superior frontal lobes were determined with an image analyser. During the two first weeks of post-embryonic development, neurogenesis decreases in the three brain structures mentioned above. However, as soon as fifteen days of age, this phenomenon is attenuated in these lobes for animals reared in enriched conditions. Our results show the influence of early experience enrichment on post-embryonic neurogenesis in structures classically involved in learning and memory processes in cuttlefish. [Poster Presentation]
Trio mating formation during copula in the hermaphrodite land snail Iberus gualtierianus L. (Gastropoda: Helicidae) Rubén Rabaneda-Bueno1, Gregorio Moreno-Rueda1, Francisco A. Rulz-Avilés1 & Rocio Márquez-Ferrando2 1 Universidad de Granada, Spain. 2 C/ Juan XXIII, Vejer de la Frontera, Cádiz, Spain. Iberus gualtierianus L (1751) is an endemic helicid from the Iberian Peninsula, whose reproduction is almost unknown. During a field study in Sierra Elvira (SE Spain) we recorded 12 copula events of this species, five of them (41.6%) consisting of three snails forming a trio. Detailed observations of several trio events showed that two individuals (α and β;) were copulating, both acting as male and female at the same time, while a third individual (γ) was interacting with one of those in the couple, acting only as a male. The process of a trio mating attempt was observed. One snail approached a couple from a recently finished trio event, and partially evaginated its penis to mate one individual within the couple, but abandoned its copulation attempt afterwards due to disturbance by researchers. In this kind of behaviour the individual playing the "intruder" strategy (γ) appears to profit from the defencelessness of the couple copulating, raising its fitness at a very low cost, while the other two individuals would be harmed, one( β) by receiving sperm from a partner that has not chosen itself and the second one (α) by sperm competition with γ .These costs can fuel the evolution, through a complex arms race, of defensive strategies against this behaviour which could explain the lack of trio formation in other species.
Life in the slow lane: dispersal of an intertidal gastropod Littorina littorea Maya Rajasekharan & Tasman Crowe, Department of Zoology, University College Dublin, Ireland. Quantitative data about the movement rates of gastropods gives a better understanding of gastropod and their interactions with the environment. Rate of movement at an individual level has several implications for survival and reproduction. In patchy rocky shores, movement rates are a limiting factor in search for suitable habitats. These habitats must have an ample food supply, low competition, sufficient protection from predators, and easy access to mates. A firm grasp on the potential for movement at a species level will dictate how large role dispersal plays in population structure and distribution. We tested experimentally whether the rate of dispersal was influenced by density, some features of the habitat or individuals at different sites or an interaction between these factors in common periwinkle Littorina littorea. Initial observations showed that the common periwinkle dispersed more rapidly from areas with naturally low population densities. We then monitored dispersal of marked periwinkles stocked at different densities in sites in two similar habitats of differing natural densities. There was no significant difference between displaced distances according to density. Reciprocal transplantation experiment revealed that intrinsic variation in the snails lead to difference in the dispersal capabilities in two sites. But on another shore winkles responded to density and there was significant difference in the movement rates in different treatment groups. Differences in this type of behaviour may indicate differences in how the snails sense and respond to their environment.
Diversity of mating behaviour within Deroceras Heike Reise, Staatliches Museum fur Naturkunde Gorlitz, PF 300154, 02806 Gorlitz, Germany Heik...@smng.smwk.sachsen.de
Do limpets orientate themselves with their heads down-slope? K Smith & R Coleman, University of Plymouth, UK The homing behaviour of limpets has stimulated much research; however, the properties of the home-scar or resting site have received less attention. Previously, it has been suggested that limpets on rocky shores lie on their home scar with the head end down-slope. It was proposed that this was a water retention mechanism, in that limpets on slopes did this so the head was immersed last and submerged first. It appeared that the observation that limpet anterior-posterior orientation was slope dependent was questionable for populations in South Devon, UK, and in addition some of the original descriptions of slope-based orientation were based on flawed analyses. We present the results of a rigorous field study, and discuss the patterns of limpets in relation to surface rugosity. [POSTER PRESENTATION] Sperm competition in Biomphalaria glabrata (Say 1818), (Gastropoda: Pulmonata), an intermediate host of Schistosoma mansoni Jaqueline A. Trigwell, Canterbury Christ Church University College, UK Biomphalaria glabrata, a simultaneous hermaphrodite freshwater snail, produces both sperm and eggs at the same time. When isolated, snails use autosperm to self-fertilise eggs; paired individuals preferentially copulate with a conspecific and use allosperm to produce outcrossed offspring. Because albinism is recessive to pigmentation, two genotypes of B. glabrata, the wild-type pigmented form and the albino form, were used in breeding experiments to investigate sperm competition. Female-acting snails paired sequentially with more than one male actor produced progeny sired by each partner. Even though some individuals produced albino and pigmented progeny in numbers that deviated significantly from expected Mendelian ratios, these were maintained within the population as a whole. Although, in evolutionary terms, an advantage may be conferred by inter- and intra-ejaculate competition, this advantage was not biased towards pigmented sperm.
Octopaminergic neuromodulation in the feeding network of the snail Lymnaea stagnalis: increasing membrane excitability by affecting voltage-evoked membrane currents A Vehovszky, H Szabb, CJH Elliott*. Balaton Limnological Institute, Hungary & *University of York, UK Octopamine acts as a polycyclic neuromodulator in the feeding network of the pond snail Lymnaea stagnalis. The mechanism is presynaptic facilitation based on the increased excitability of particular (SO, N1L) feeding inteneurons. Application of octopamine also increased the excitability on B1 and B4 motoneurons but not the B2 neuron. We tested the cellular mechanism using the voltage clamp technique. Neither outward current (IA or IK) was modulated by 10µ;M octopamine, though the fast inward (sodium) component increased by 33 and 45% in the B1 and 64 but not on the B2 motoneuron. Moreover, 10µM octopamine blocked 85% of the HVA component of a slower (Ca-dependent) inward current. The increase in the fast inward current by octopamine may be responsible for increased excitability of B1 and B4 feeding motoneurons, and the lowered firing threshold of interneurons. Decrease in calcium currents may decrease accommodation through reduction in (Ca- dependent) outward potassium current. [POSTER PRESENTATION]
Rhumina Bustos-Pezo and Ruth Kirk at the registration desk
Cruise down Thames to Hampton Court
Poster Session
Richard Cook sets up a session in the lecture theatre |
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While
the role of hormones in molluscan reproduction is supported by a large
body of evidence, little attention has been directed toward neural controls.
We study how oocytes are released from the ovotestis (ovulation) and
how allosperm is released from the seminal vesicle (ejaculation). Sensory
innervation of the ovotestis provides a tonic afferent signal that informs
the CNS of the number of mature oocytes available for fertilization.
A threshold strength of this signal is necessary, but not sufficient,
for egg laying to occur. Ovulation, once initiated, is aided by activity
in motor nerve fibres innervating the proximal hermaphroditic duct,
causing peristaltic contractions of the duct wall and acceleration of
ciliary beating in the interior of the duct. The muscular contractions
are mediated by both serotonin and acetylcholine, whereas the ciliary
effect is mediated by serotonin. The release of sperm from the seminal
vesicle appears to be controlled through innervation of the distal hermaphroditic
duct. Electrical stimulation of the relevant nerve branch causes back-and-forth
movements of sperm in the hermaphroditic duct resulting in a net outward
flow. Direct application of acetylcholine and serotonin also elicit
the release of sperm, but only if the two substances are applied sequentially.
Cephalopods
have a skin display system using chromatophores and underlying reflective
iridophores with such sophistication that they can literally paint any
pattern on their skin. How can they manipulate skin displays to produce
meaning and communicate with others? While Sepioteuthis sepoidea
squids use it to indicate internal state, the display system also has
directionality of pattern production. Squid always produce the warning
Lateral Silver and often the agonistic/status Zebra unilaterally. They
can produce startle Dynamic dots at four locations on the fin/mantle
intersection. Adults generally produce the two posterior dots, yet when
fish or other potential predators approach they may produce a different
pair or even one dot. The directionality of dots is biased towards the
approaching animal and not towards specifics, to repel the fish and
not to warn other squid of its presence. Finally, squid may address
two different displays laterally to two different receivers at once,
a phenomenon called Double Signalling. This directionality casts doubt
on the idea that skin displays are merely external signals of internal
affective state and raises questions about how a neural control system
can program the skin to send two messages at once in two directions.
Deroceras
is the largest genus of terrestrial slugs (>100 species). Although
each species is externally indistinguishable from others, penis morphology
and mating behaviour are highly diverse. The penis varies in shape and
has a variety of internal and external structures, some truly bizarre.
Their exact function is usually unknown. Mating behaviour can also provide
a useful taxonomic tool, particularly to investigate sibling species
in cases of high intraspecific morphological variability. I review mating
behaviour in Deroceras based on published records and my own
observations (data on 13 species altogether). I analyse patterns common
to all Deroceras, and the inter- and intraspecific variability,
stressing which characters are potentially useful for taxonomy. The
most important species differences involve durations of certain mating
phases, the presence and nature of trail following in the recognition
phase, the nature and intensity of stroking with the stimulator during
courtship, and the aggressiveness of the courtship behaviour. Some species
evert a flagellum at copulation, but this depends only on whether this
structure is present. I propose that the radiation of mating behaviours
and associated structures may have been driven by an arms race resulting
from conflicting interests of mating partners over sperm donation and
usage. This could also have increased the rate of speciation. 
