Biology subjects

Tolstenkov, O.

Publications and source records attributed to Tolstenkov, O..

6 recordsLinked to original sources

bioRxiv2026

Annelid eye evolution revealed by developmental, ultrastructural, and connectome analyses of cerebral eyes in Malacoceros fuliginosus

Eye evolution has long attracted interest, yet how multiple cerebral eyes within a lineage originate and diversify remains unclear. Annelids display exceptional diversity in eye number and structure, but the homology and function of distinct eye pairs are poorly understood. Here we investigate the cerebral eyes of the sedentary annelid Malacoceros fuliginosus using an integrated developmental, molecular, ultrastructural, and connectomic approach. We show that both the early-developing ventral and later-developing dorsal eyes are simple, few-celled, inverted rhabdomeric eyes that express transcription factors with conserved roles in animal eye development. Two r-opsin paralogs and distinct neurotransmitters are differentially expressed in different photoreceptor cells of the eyes. Ultrastructural reconstructions across larval development reveal differences in cellular composition and growth dynamics, while axonal tracing shows that photoreceptors from ventral and dorsal eyes project to overlapping regions of the larval brain. The overall organization and projections resemble those described in the errant annelid Platynereis dumerilii. Together, these data support the hypothesis that an ancestral cerebral eye duplicated early in annelid evolution, giving rise to multiple eye pairs with stage-specific functions.

evolutionary biology↗

bioRxiv2025

Behavioral ontogeny in a pelagic tunicate reveals the deep origins of chordate behavioral developmental plasticity.

Behavioral developmental plasticity refers to the lasting changes in an organisms behavior that occur during development in response to external and internal cues, enhancing survival and reproduction. While well studied in vertebrates, its occurrence in other chordates, including tunicates, the closest relatives of vertebrates, remains unclear. We built a behavioral atlas of the planktonic tunicate Oikopleura dioica across its life cyclefrom larval to adult stages using high-throughput tracking and unsupervised analysis. Swimming kinematics, exploration, and thigmotaxis increased with development. Adults exhibit a unique innovation, known as the house, a complex extracellular filtration structure encasing the animal trunk, which drastically alters locomotion and exploration compared to free-swimming individuals. Postural variation during ontogeny is captured by seven basic shapes ("eigenoikopleuras"), with complex shapes becoming more frequent over time. Spatiotemporal embedding and Hidden Markov modeling revealed that behavioral refinement arises from changes in motor modules and their transitions. House occupancy similarly shifts these modules, indicating context-specific specialization. This continuous behavioral maturation parallels Oikopleuras neotenic morphology, retaining a larval body plan unlike other tunicates. Our atlas provides a quantitative framework for exploring the evolution of behavioral developmental plasticity in chordates.

animal behavior and cognition↗

bioRxiv2025

The evolution of embodied postural dynamics underlies behavioral diversity in benthic sessile chordate

Benthic animals live on or in the seafloor, a habitat known as the benthic zone. These bottom-dwelling organisms account for the largest fraction of animal diversity in our seas, playing vital roles in nutrient cycling, sediment stabilization and the broader food webs. Historically, the behavioral repertoire of benthic animals attached permanently to the sea floor has been considered as extremely limited (if at all present), reflecting an evolutionary adaptation to their sessile lifestyle and simplified nervous systems. Here, we overturn this view by studying the spontaneous and stimulus evoked behavioral repertoire of the basal chordate Ciona intestinalis which has a benthic sessile adult stage. We found that Ciona adults transition between three main postural engagement behavioral states. These are defined by different body part kinematics and postural dynamics characterised by changes in body shape configuration as opposed to locomotion. Transitions between states can occur probabilistically in spontaneously behaving animals suggesting that they can be internally generated by the simple brain of an adult Ciona. Importantly, using spatiotemporal embedding of postural features, we constructed a behavioral space for Ciona adults, which was divided into 18 stereotyped behavioral modes revealing the unappreciated richness of adult Ciona behaviors. Our analysis showed that Ciona adults can deploy in a selective manner these behavioral modules to elicit distinct responses to different mechanical stimuli, suggesting the presence of a sensory context dependent regulation of behavior in these benthic organisms. Our study raises the possibility that embodied postures is underlie the evolution of behavioral repertoires in sessile benthic animals.

animal behavior and cognition↗

bioRxiv2025

The cellular and behavioral blueprints of chordate rheotaxis.

The oceans are filled with life-forms exhibiting complex adaptations to help navigate fluid environments and take advantage of fluid motion to locomote and disperse. However, the neuronal and behavioral underpinnings of navigating in fluid environments outside vertebrates are poorly understood. We present behavioral and computational modelling-based evidence that the pre-vertebrate chordate Ciona intestinalis actively modulates its heading and angular velocities to counter oncoming flows and perform positive rheotaxis. We demonstrate that a distributed network of ciliated peripheral sensory neurons is responsible for sensing hydrodynamic information such as flow velocity and direction. Pharmacological removal of sensory cilia impedes rheotactic behavior and reduces stimulus evoked neuronal activity. Whole-brain calcium imaging experiments reveal that the central nervous system of Ciona can encode the onset and offset of flow, flow direction, and flow velocity, suggesting that miniature chordate brain is capable of surprisingly sophisticated computations.

neuroscience↗

bioRxiv2023

When offspring outsmarting parents: Neuronal genes expression in two generations of marine parasitic worm

Trematodes, or flukes, cause disease in millions of people, impact animal health, and alter the functional organization of biological communities. During the transition from the intramolluscan redia to the free-living cercaria stage in a complex life cycle of trematodes, extensive anatomical and behavioral modifications occur, enabling the cercaria to locate and infect the next host in the complex water environment. However, the functional changes that occur in the nervous system during this shift are not well understood. We used a de novo transcriptome to characterize the molecular building blocks of the trematode nervous system and identify pathways that may underlie differences in nervous system function between the rediae and cercariae stages of the Cryptocotyle lingua, marine trematode species causing problems for fisheries. Our results confirmed the streamlined molecular toolkit of these parasitic trematodes, including the absence of certain key signaling pathways and ion channels. We documented the loss of nitric oxide synthase not only in C. lingua but also in the entire phylum Platyhelminthes. We identified several neuronal genes upregulated in dispersal larvae, including genes involved in synaptic vesicle trafficking, TRPA channels, G-protein coupled receptors, and surprisingly nitric oxide receptors soluble guanylate cyclase. Validation of these findings using neuronal markers and in situ hybridization allowed us to hypothesize the protein function in relation to the adaptations and host-finding strategy of the dispersal larva. Our results and established behavior quantification toolkit for cercaria motility provide a foundation for future research on the behavior and physiology of parasitic flatworms, with potential implications for developing antiparasitic measures. HighlightsO_LIWe utilized a behavior quantification toolkit and described essential neuronal genes in a handy model species, enabling the study of fluke neurobiology at the systems level. C_LIO_LIWe characterized and validated neuronal gene expression profiles in cercarial embryos within rediae and swimming host-searching cercariae. C_LIO_LIThe streamlined molecular toolkit of parasites reveals the absence of important signaling pathways and ion channels in their nervous system. C_LIO_LIWe documented loss of nitric oxide synthase in flatworms. C_LIO_LIThe expression pattern of nitric oxide receptors, soluble guanylate cyclases, upregulated in swimming larvae, emphasizes their crucial involvement in the dispersal process. C_LIO_LITwo upregulated TRPA channels in cercaria are primarily expressed in cilia and peripheral neurons, emphasizing their importance in host finding. C_LI

zoology↗

bioRxiv2018

Functionally asymmetric motor neurons coordinate locomotion of Caenorhabditis elegans

Invertebrate nervous systems are valuable models for fundamental principles of the control of behavior. Ventral nerve cord (VNC) motor neurons in Caenorhabditis elegans represent one of the best studied locomotor circuits, with known connectivity and functional information about most of the involved neuron classes. However, for one of those, the AS motor neurons (AS MNs), no physiological data is available. Combining specific expression and selective illumination, we precisely targeted AS MNs by optogenetics and addressed their role in the locomotion circuit. After photostimulation, AS MNs induce currents in post-synaptic body wall muscles (BWMs), exhibiting an initial asymmetry of excitatory output. This may facilitate complex regulatory motifs for adjusting direction during navigation. By behavioral and photo-inhibition experiments, we show that AS MNs contribute to propagation of the antero-posterior body wave during locomotion. By Ca2+-imaging in AS MNs and in their synaptic partners, we also reveal that AS MNs play a role in mediating forward and backward locomotion by integrating activity of premotor interneurons (PINs), as well as in coordination of the dorso-ventral body wave. AS MNs do not exhibit pacemaker properties, but potentially gate VNC central pattern generators (CPGs), as indicated by ceasing of locomotion when AS MNs are hyperpolarized. AS MNs provide positive feedback to the PIN AVA via gap junctions, a feature found also in other locomotion circuits. In sum, AS MNs have essential roles in coordinating locomotion, combining several functions, and emphasizing the compressed nature of the C. elegans nervous system in comparison to higher animals.\n\nHighlightsA class of motor neurons with unidentified function - AS cholinergic motor neurons - was characterized in C. elegans.\n\nAS neurons show asymmetry in both input and output and are specialized in coordination of dorso-ventral undulation bends.\n\nAS neurons mediate antero-posterior propagation of the undulatory body wave during locomotion.\n\nAS neurons integrate signals for forward and reverse locomotion from premotor interneurons and may gate ventral nerve cord central pattern generators (CPGs) via gap junctions.

neuroscience↗