Neural Correlates of Swimming Behavior in Melibe leonina

The nudibranch Melibe leonina swims by rhythmically bending from side to side at a frequency of 1 cycle every 2–4 s. The objective of this study was to locate putative swim motoneurons (pSMNs) that drive these lateral flexions and determine if swimming in this species is produced by a swim central pattern generator (sCPG). In the first set of experiments, intracellular recordings were obtained from pSMNs in semi-intact, swimming animals. About 10–14 pSMNs were identified on the dorsal surface of each pedal ganglion and 4–7 on the ventral side. In general, the pSMNs in a given pedal ganglion fired synchronously and caused the animal to flex in that direction, whereas the pSMNs in the opposite pedal ganglion fired in anti-phase. When swimming stopped, so did rhythmic pSMN bursting; when swimming commenced, pSMNs resumed bursting. In the second series of experiments, intracellular recordings were obtained from pSMNs in isolated brains that spontaneously expressed the swim motor program. The pattern of activity recorded from pSMNs in isolated brains was very similar to the bursting pattern obtained from the same pSMNs in semi-intact animals, indicating that the sCPG can produce the swim rhythm in the absence of sensory feedback. Exposing the brain to light or cutting the pedal-pedal connectives inhibited fictive swimming in the isolated brain. The pSMNs do not appear to participate in the sCPG. Rather, they received rhythmic excitatory and inhibitory synaptic input from interneurons that probably comprise the sCPG circuit

The western atlantic Tritoniidae

As sete Tritoniidae do Atlântico Ocidental são descritas e desenhadas. Os caracteres sistemáticos são discutidos e foram feitas lista e chave para os gêneros das Tritoniidae. A distribuição de Marionia cucullata é estendida para o norte até o Estreito da Flórida. As novas espécies, Tritonia eriosi da Ilha dos Lobos, Uruguai, e Marionia tedi do Estreito da Florida são descritas e desenhadas. Tritonia odhneri Tardy, 1963, da Bretanha é pré-ocupada por Tritonia odhne- ri Marcus, 1959, do Chile. Propondo chamar a espécie de Tardy de Tritonia nils- odhneri, nom. nov. A Marionia cucullata Vicente & Arnaud, 1979 da Terra Adelie, tem processos velares simples, e placas gástricas não são mencionadas. Portanto não pertence ao gênero Marionia. Tritonia episcopalis Bouchet, 1977, é provavelmente uma Tritoniella devido à forma da ponta do seu penis

Swimming Behavior of the Nudibranch Melibe leonina

Swimming in the nudibranch Melibe leonina consists of five types of movements that occur in the following sequence: (1) withdrawal, (2) lateral flattening, (3) a series of lateral flexions, (4) unrolling and swinging, and (5) termination. Melibe swims spontaneously, as well as in response to different types of aversive stimuli. In this study, swimming was elicited by contact with the tube feet of the predatory sea star Pycnopodia helianthoides, pinching with forceps, or application of a 1 M KCl solution. During an episode of swimming, the duration of swim cycles (2.7 ± 0.2 s [mean ± SEM], n = 29) and the amplitude of lateral flexions remained relatively constant. However, the latency between the application of a stimulus and initiation of swimming was more variable, as was the duration of an episode of swimming. For example, when touched with a single tube foot from a sea star (n = 32), the latency to swim was 7.0 ± 2.4 s, and swimming continued for 53.7 ± 9.4 s, whereas application of KCl resulted in a longer latency to swim (22.3 ± 4.5 s) and more prolonged swimming episodes (174.9 ± 32.1 s). Swimming individuals tended to move in a direction perpendicular to the long axis of the foot, which propelled them laterally when they were oriented with the oral hood toward the surface of the water. The results of this study indicate that swimming in Melibe, like that in several other molluscs, is a stereotyped fixed action pattern that can be reliably elicited in the laboratory. These characteristics, along with the large identifiable neurons typical of many molluscs, make swimming in this nudibranch amenable to neuroethological analyses

Evolution der Cephalic Sensory Organs innerhalb der Opisthobranchia

Das Ziel der vorliegenden Doktorarbeit war es, die Evolution der Kopfsinnesorgane der Opisthobranchia zu rekonstruieren. Bei den Opisthobranchia handelt es sich um eine äußerst diverse Gruppe überwiegend mariner Gastropoden innerhalb der Euthyneura. Die Kopfsinnesorgane oder cephalic sensory organs (CSOs) weisen innerhalb der verschiedenen Großgruppen der Opisthobranchia eine sehr hohe morphologische Variabilität auf, und finden ihre Ausprägung in verschiedenen Formen von Labialtentakeln, Mundsegeln, Rhinophoren, Lippenorganen, Kopfschilden und dem so genannten Hancockschen Organ. Die Homologieverhältnisse der CSOs waren bislang ungeklärt. Der Ansatz der vorliegenden Studie war es, neurobiologische Methoden zu verwenden um die CSOs zu charakterisieren und zu homologisieren, da sich bisherige Methoden wie Histologie und anatomische Studien als unzureichend herausgestellt haben, die Homologieverhältnisse zu klären. Die dabei verwendeten Methoden wurden bislang nur in funktionellen Fragestellungen verwendet, daher stellt dieser Ansatz eine Neuerung in der vergleichenden Morphologie dar. Die untersuchten Taxa umfassten die folgenden Großgruppen, Aplysiomorpha (Aplysia punctata, Aplysia californica, Petalifera petalifera), Pleurobranchomorpha (Pleurobranchaea meckeli, Berthella plumula), Nudibranchia (Archidoris pseudoargus), Cephalaspidea (Haminoea hydatis, Scaphander lignarius) und Acteonoidea (Acteon tornatilis). Um eine Rekonstruktion der Evolution zu ermöglichen wurden weiterhin Außengruppen wie die Caenograstropoda (Littorina littorea) und die Pulmonata (Achatina fulica) untersucht. Als Ergebnis stellte sich heraus, dass die zellulären Innervierungsmuster überraschend stark konservierte Strukturen darstellen, welche sich eignen, um die zerebralen Nerven innerhalb der untersuchten Taxa zu homologisieren. Hierbei ist anzumerken, dass die Opisthobranchia und die Pulmonata zwei Paar Kopfsinnesorgane und in der Regel vier zerebrale Nerven besitzen, die Caenogastropoda jedoch nur ein Paar Tentakel und drei zerebrale Nerven. Zusammenfassend lässt sich erklären, dass es anhand der verwendeten neurobiologischen Methoden möglich war, plausibel gestützte Homologiehypothesen für die CSOs der Opisthobranchia zu formulieren. Anstelle früher verwendeter, zum Teil widersprüchlicher Begriffe wie Labialtentakel oder Rhinophoren wurden Kategorien von CSOs postuliert. Diese Kategorien sind Lip (Lippe), ASOa und ASOb (der zerebrale Nerv der innerhalb der Euthyneura die ASOs innerviert ist gegabelt und innerviert Strukturen mit wahrscheinlich unterschiedlichen Funktionen) und die PSOs. Nach der erfolgten Homologisierung der CSOs wurde ihre Evolution unter Berücksichtigung der sparsamsten Erklärung, auf der Grundlage einer molekularen Phylogeniehypothese a posteriori rekonstruiert. Es wurde postuliert, dass das Grundmuster der Euthyneura, zwei paar Kopfsinnesstrukturen besitzt. Die ASOs sind hierbei noch relativ unspezialisiert und wurden als lobenartige Strukturen postuliert, die PSOs hingegegen als eine Art basale Tentakel (Rhinophoren), welche innerhalb der Opisthobranchia unterschiedliche Ausprägung erfuhren und homolog zu den Ommatophoren der Pulmonaten sind. Damit widerlegte die vorliegende Studie die bislang gängige Annahme eines Kopfschildes und des Hancockschen Organs im Grundmuster der Opisthobranchia. Es wird davon ausgegangen, dass diese Organe eine Anpassung an eine grabende Lebensweise sind, bei der Tentakel, als mechanischer Belastung ausgesetzte Strukturen, eher hinderlich sind.The term cephalic sensory organ (CSO) is used for specialised structures in the head region of adult Opisthobranchia. These sensory organs show a high diversity in form and function, and the gross morphology of these organs differs considerably among taxa. They can be identified as cephalic shields, oral veils, Hancocks organs, lip organs, rhinophores or oral tentacles. Because of this extremely high diversity, the homology and the evolution of these organs have not been clarified yet. My intention was to use neuroanatomical data sets in order to find putative homologous CSOs. In this study, I will show data about immunohistochemical neurotransmitter content and cellular innervation patterns and their applicability as morphological characters for the homologisation of structures. I support earlier investigations that neurotransmitter content is often related to function. In contrast, axonal tracing patterns can be used to homologise nerves. Overall the aim of this study was to reconstruct the evolution of the CSOs of the Opisthobranchia, by projecting our neuroanatomical data sets onto a molecular phylogeny

Central pattern generator for swimming in Melibe

The nudibranch mollusc Melibe leonina swims by bending from side to side. We have identified a network of neurons that appears to constitute the central pattern generator (CPG) for this locomotor behavior, one of only a few such networks to be described in cellular detail. The network consists of two pairs of interneurons, termed `swim interneuron 1\u27 (sint1) and `swim interneuron 2\u27 (sint2), arranged around a plane of bilateral symmetry. Interneurons on one side of the brain, which includes the paired cerebral, pleural and pedal ganglia, coordinate bending movements toward the same side and communicate via non-rectifying electrical synapses. Interneurons on opposite sides of the brain coordinate antagonistic movements and communicate over mutually inhibitory synaptic pathways. Several criteria were used to identify members of the swim CPG, the most important being the ability to shift the phase of swimming behavior in a quantitative fashion by briefly altering the firing pattern of an individual neuron. Strong depolarization of any of the interneurons produces an ipsilateral swimming movement during which the several components of the motor act occur in sequence. Strong hyperpolarization causes swimming to stop and leaves the animal contracted to the opposite side for the duration of the hyperpolarization. The four swim interneurons make appropriate synaptic connections with motoneurons, exciting synergists and inhibiting antagonists. Finally, these are the only neurons that were found to have this set of properties in spite of concerted efforts to sample widely in the Melibe CNS. This led us to conclude that these four cells constitute the CPG for swimming. While sint1 and sint2 work together during swimming, they play different roles in the generation of other behaviors. Sint1 is normally silent when the animal is crawling on a surface but it depolarizes and begins to fire in strong bursts once the foot is dislodged and the animal begins to swim. Sint2 also fires in bursts during swimming, but it is not silent in non-swimming animals. Instead activity in sint2 is correlated with turning movements as the animal crawls on a surface. This suggests that the Melibe motor system is organized in a hierarchy and that the alternating movements characteristic of swimming emerge when activity in sint1 and sint2 is bound together

Modulation of swimming in the gastropod Melibe leonina by nitric oxide

Nitric oxide (NO) is a gaseous intercellular messenger produced by the enzyme nitric oxide synthase. It has been implicated as a neuromodulator in several groups of animals, including gastropods, crustaceans and mammals. In this study, we investigated the effects of NO on the swim motor program produced by isolated brains and by semi-intact preparations of the nudibranch Melibe leonina. The NO donors sodium nitroprusside (SNP, 1 mmol l–1) and S-nitroso-N-acetylpenicillamine (SNAP, 1 mmol l–1) both had a marked effect on the swim motor program expressed in isolated brains, causing an increase in the period of the swim cycle and a more erratic swim rhythm. In semi-intact preparations, the effect of NO donors was manifested as a significant decrease in the rate of actual swimming. An NO scavenger, reduced oxyhemoglobin, eliminated the effects of NO donors on isolated brains, supporting the assumption that the changes in swimming induced by donors were actually due to NO. The cGMP analogue 8-bromoguanosine 3′,5′-cyclic monophosphate (1 mmol l–1) produced effects that mimicked those of NO donors, suggesting that NO is working via a cGMP-dependent mechanism. These results, in combination with previous histological studies indicating the endogenous presence of nitric oxide synthase, suggest that NO is used in the central nervous system of Melibe leonina to modulate swimming

Evolution of swimming behaviors in nudibranch molluscs: A comparative analysis of neural circuitry

Behaviors are a product of underlying neural circuits, yet there is a paucity of mechanistic information about how nervous systems contribute to the repeated evolution of similar behaviors. Theoretical studies have predicted that the same behavioral output can be generated by neural circuits with different properties. Here, we test the theory in biological circuits by comparing the central pattern generator (CPG) circuits underlying swimming behaviors in nudibranchs (Mollusca, Gastropoda, Euthyneura, Nudipleura). In comparative studies of neural circuits, neurotransmitter content can serve as landmarks or molecular markers for neuron types. Here, we created a comprehensive map of GABA-immunoreactive neurons in six Nudipleura species. None of the known swim CPG neurons were GABA-ir, but they were located next to identifiable GABA-ir neurons/clusters. Despite strong conservation of the GABA-ergic system, there were differences, particularly in the buccal ganglia, which may represent adaptive changes. We applied our knowledge of neurotransmitter distribution along with morphological traits to identify the neuron type Si1 in Flabellina, a species that swims via whole body left-right (LR) flexions and in Tritonia, a dorsal-ventral (DV) swimming species. Si1 is a CPG member of the LR species Melibe, whereas its homologue in the LR species Dendronotus is not. In Flabellina, Si1 was part of the LR CPG and despite having similar synaptic connections as Flabellina and Melibe, Si1 in Tritonia was not part of its DV swim CPG. Side by side circuit comparison of Flabellina, Melibe and Dendronotus revealed different combinations of circuit architecture and modulation resulting in different circuit configurations for LR swimming. This includes differences in the role and activity pattern of Si1, sensitivity to curare and the effect of homologues of C2, a DV CPG neuron, on the LR motor pattern. These results collectively reveal three different circuit variations for generating the same behavior. It suggests that the neural substrate from which behaviors arise is phylogenetically constrained. While this neural substrate can be configured in multiple different ways to generate the same outcome, the possibilities are finite and, as seen here, similar structural and functional neural motifs are used in the evolution of these circuits

A Comparative Analysis of the Neural Basis for Dorsal-Ventral Swimming in the Nudipleura

Despite having similar brains, related species can display divergent behaviors. Investigating the neural basis of such behavioral divergence can elucidate the neural mechanisms that allow behavioral change and identify neural mechanisms that influence the evolution of behavior. Fewer than three percent of Nudipleura (Mollusca, Opisthobranchia, Gastropoda) species have been documented to swim. However, Tritonia diomedea and Pleurobranchaea californica express analogous, independently evolved swim behaviors consisting of rhythmic, alternating dorsal and ventral flexions. The Tritonia and Pleurobranchaea swims are produced by central pattern generator (CPG) circuits containing homologous neurons named DSI and C2. Homologues of DSI have been identified throughout the Nudipleura, including in species that do not express a dorsal-ventral swim. It is unclear what neural mechanisms allow Tritonia and Pleurobranchaea to produce a rhythmic swim behavior using homologous neurons that are not rhythmic in the majority of Nudipleura species. Here, C2 homologues were also identified in species that do not express a dorsal-ventral swim. We found that certain electrophysiological properties of the DSI and C2 homologues were similar regardless of swim behavior. However, some synaptic connections differed in the non-dorsal-ventral swimming Hermissenda crassicornis compared to Tritonia and Pleurobranchaea. This suggests that particular CPG synaptic connections may play a role in dorsal-ventral swim expression. DSI modulates the strength of C2 synapses in Tritonia, and this serotonergic modulation appears to be necessary for Tritonia to swim. DSI modulation of C2 synapses was also found to be present in Pleurobranchaea. Moreover, serotonergic modulation was necessary for swimming in Pleurobranchaea. The extent of this neuromodulation also correlated with the swimming ability in individual Pleurobranchaea; as the modulatory effect increased, so too did the number of swim cycles produced. Conversely, DSI did not modulate the amplitude of C2 synapses in Hermissenda. This indicates that species differences in neuromodulation may account for the ability to produce a dorsal-ventral swim. The results indicate that differences in synaptic connections and neuromodulatory dynamics allow the expression of rhythmic swim behavior from homologous non-rhythmic components. Additionally, the results suggest that constraints on the nervous system may influence the neural mechanisms and behaviors that can evolve from homologous neural components

Tritonia nilsodhneri marcus Ev., 1983 (Gastropoda, heterobranchia, tritoniidae): First records for the adriatic sea and new data on ecology and distribution of mediterranean populations

The nudibranch Tritonia nilsodhneri, usually feeding on a variety of gorgoniacean species, is known from different localities of the eastern Atlantic Ocean and the Mediterranean Sea. Knowledge of the host preferences of the Mediterranean populations is still scarce. Few records of this nudibranch have been reported from the eastern Mediterranean basin. With this report, the occurrence of T. nilsodhneri within the Mediterranean basin is extended to the Adriatic Sea. Furthermore, the list of the host species associated to the Mediterranean populations for feeding habits is increased from two up to five. Mediterranean specimens of T. nilsodhneri were observed for the first time feeding and spawning on Leptogorgia sarmentosa, Eunicella cavolini and E. labiata. Finally, these last two Gorgoniidae species are also reported here as a new host species for T. nilsodhneri

Neuronal Responses to Water Flow in the Marine Slug Tritonia diomedea

The marine slug Tritonia diomedea mustrely on its ability to touch and smell in order to navigate because it is blind. The primaryfactor that influences its crawling direction is the direction of water flow (caused bytides in nature). The sensory cells that detect flow and determine flow directionhave not been identified. The lateral branch of Cerebral Nerve 2 (latCeN2) has beenidentified as the nerve that carries sensory axons to the brain from the flow receptors inthe oral tentacles. Backfilling this nerve to the brain resulted in the labeling of a numberof cells located throughout the brain. Most of the labeled cells are concentrated in the cerebral ganglion where the nerve enters thebrain. The medial and lateral branches of CeN2 were backfilled for comparison of thepattern of cells from each nerve. A map of the cells innervated by latCeN2 reveals thelocation of the stained cells. Extracellular recording from latCeN2 revealed itsinvolvement in the detection of water flow and orientation. The nerve becomes activein response to water flow stimulation. Intracellular recordings of the electricalactivity of these cells in a live animal will be the next step to determine if these cells arethe flow receptors