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Does the sentience framework imply all animals are sentient?
... The project proposed by K&F follows an emerging tradition within the sciences of animal cognition more generally, which seeks to explore the dimensions and variety within a cognitive trait such as consciousness (Andrews, 2022;Birch, Schnell and Clayton, 2020;Veit, 2023) or affect (Browning, 2022), rather than simply map its presence or absence. Such a research programme can tell us more about what it is like to be different types of animal, and adding an understanding of introspective processes can only help deepen such an understanding. ...
The study of introspection has, up until now, been predominantly human-centric, with regrettably little attention devoted to the question of whether introspection might exist in non-humans, such as animals and artificial intelligence (AI), and what distinct forms it might take. In their target article, Kammerer and Frankish (this issue) aim to address this oversight by offering a non-anthropocentric framework for understanding introspection that could be used to address these questions. However, their discussions on introspection in animals and AIs were quite brief. In this commentary, we will build on their suggestions to offer some methodological guidance for how future research into introspection in animals and AIs might proceed.
... For example, an animal might not show indicators of positive affective states, such as feeling happiness, but still feel pain. For this reason, we caution against using only positive emotionlike states as indicators of sentience, and to extrapolate from these to the possibility that animals feel pain (Andrews 2022;de Waal 2022;Souza Valente 2022). Although assessing positive experiences can have important effects on improving animal welfare (Boissy et al. 2007), the risk of false negative diagnoses of pain is potentially more serious for welfare considerations than false positives. ...
Pain is an aversive subjective experience that is consciously experienced as unpleasant. Causing unnecessary pain to animals is ethically wrong because pain is intrinsically aversive. Trillions of insects are used, harmed and killed per year, but they are excluded from animal welfare legislation because they have not yet been tested for their capacity for pain. Therefore, the evaluation of whether insects can feel pain is a necessity. This case describes potential ways to measure pain in an animal for which there is currently little or no published research about which behaviours might indicate pain.
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Animal nervous system organization is crucial for all body functions and its disruption can lead to severe cognitive and behavioural impairment¹. This organization relies on features across scales—from the localization of synapses at the nanoscale, through neurons, which possess intricate neuronal morphologies that underpin circuit organization, to stereotyped connections between different regions of the brain². The sheer complexity of this organ means that the feat of reconstructing and modelling the structure of a complete nervous system that is integrated across all of these scales has yet to be achieved. Here we present a complete structure–function model of the main neuropil in the nematode Caenorhabditis elegans—the nerve ring—which we derive by integrating the volumetric reconstructions from two animals with corresponding³ synaptic and gap-junctional connectomes. Whereas previously the nerve ring was considered to be a densely packed tract of neural processes, we uncover internal organization and show how local neighbourhoods spatially constrain and support the synaptic connectome. We find that the C. elegans connectome is not invariant, but that a precisely wired core circuit is embedded in a background of variable connectivity, and identify a candidate reference connectome for the core circuit. Using this reference, we propose a modular network architecture of the C. elegans brain that supports sensory computation and integration, sensorimotor convergence and brain-wide coordination. These findings reveal scalable and robust features of brain organization that may be universal across phyla.
Sleep behaviors are observed even in nematodes and arthropods, yet little is known about how sleep-regulatory mechanisms have emerged during evolution. Here, we report a sleep-like state in the cnidarian Hydra vulgaris with a primitive nervous organization. Hydra sleep was shaped by homeostasis and necessary for cell proliferation, but it lacked free-running circadian rhythms. Instead, we detected 4-hour rhythms that might be generated by ultradian oscillators underlying Hydra sleep. Microarray analysis in sleep-deprived Hydra revealed sleep-dependent expression of 212 genes, including cGMP-dependent protein kinase 1 (PRKG1) and ornithine aminotransferase. Sleep-promoting effects of melatonin, GABA, and PRKG1 were conserved in Hydra However, arousing dopamine unexpectedly induced Hydra sleep. Opposing effects of ornithine metabolism on sleep were also evident between Hydra and Drosophila, suggesting the evolutionary switch of their sleep-regulatory functions. Thus, sleep-relevant physiology and sleep-regulatory components may have already been acquired at molecular levels in a brain-less metazoan phylum and reprogrammed accordingly.
Across species, sleep is characterized by a complex architecture. Sleep deprivation is a classic method to study the consequences of sleep loss, which include alterations in the activity of sleep circuits and detrimental consequences on well being. Automating the observation and manipulation of sleep is advantageous to study its regulation and functions. Caenorhabditis elegans shows sleep behavior similar to other animals that have a nervous system. However, a method for real-time automatic sleep detection that allows sleep-specific manipulations has not been established for this model animal. Also, our understanding of how sleep deprivation affects sleep neurons in this system is incomplete. Here we describe a system for real-time automatic sleep detection of C. elegans grown in microfluidic devices based on a frame-subtraction algorithm using a dynamic threshold. As proof of principle for this setup, we used automated mechanical stimulation to perturb sleep behavior and followed the activity of the sleep-active RIS neuron. We show that our system can automatically detect sleep bouts and deprive worms of sleep. We found that mechanical stimulation generally leads to the activation of the sleep-active RIS neuron, and this stimulation-induced RIS depolarization is most prominent during sleep deprivation.
Oxytocin has a conserved role in regulating animal social behaviour including parental-offspring interactions. Recently an oxytocin-like neuropeptide, nematocin, and its cognate receptors have been identified in the nematode Caenorhabditis elegans. We provide evidence for a pheromone signal produced by C. elegans larvae that modifies the behaviour of adult animals in an oxytocin-dependent manner increasing their probability of leaving a food patch which the larvae are populating. This increase is positively correlated to the size of the larval population but cannot be explained by food depletion nor is it modulated by biogenic amines, which suggest it is not an aversive behaviour. Moreover, the food-leaving behaviour is conspecific and pheromone dependent: C. elegans adults respond more strongly to C. elegans larvae compared to other nematode species and this effect is absent in C. elegans daf-22 larvae which are pheromone deficient. Neurotransmitter receptors previously implicated in C. elegans foraging decisions NPR-1 and TYRA-3, for NPY-like neuropeptides and tyramine respectively, do not appear to be involved in oxytocin-dependent adult food-leaving. We conclude oxytocin signals within a novel neural circuit that regulates parental-offspring social behaviour in C. elegans and that this provides evidence for evolutionary conservation of molecular components of a parental decision making behaviour.
Patterns of larval release, dispersal and settlement in sponges are poorly understood despite their significance in explaining
adult ecology. Time of release, swimming speeds, phototaxis and vertical migration were quantified for larvae of the dictyoceratid
sponge Coscinoderma matthewsi. The influence of cues associated with biofilms and coral rubble on larval settlement and metamorphosis was also measured.
C. matthewsi is a brooding sponge and releases tufted parenchymellae larvae during the day. Upon release, larvae (>90%) have no phototactic
response, maintaining their position at the water surface for 80min±0 (mean±SE) regardless of a light cue (natural daylight)
before exhibiting negative phototaxis. At 28h post-release, the majority of larvae (94.7%±6.1) exposed to light from the
surface migrated to the bottom and assumed a demersal phase. Without light, larvae occupied the surface for up to 28h post-release
(89.3%±1.8) before migrating to the bottom. Larvae did not settle gregariously and began to settle and metamorphose after
28h post-release without a cue. Settlement and metamorphosis were faster in the presence of a biofilm (settlement=15.0%±8.7
and metamorphosis=12.5%±9.5 at 28h post-release), while the addition of coral rubble accelerated metamorphosis further
(settlement=10.0%±4.1 and metamorphosis=27.5%±10.3 at 28h post-release) compared to controls (sterile surfaces) (settlement=0%
and metamorphosis=0% at 28h post-release). However, both biofilms and coral rubble decrease total metamorphosis (control=92.5%±4.8,
biofilms=67.5%±7.5 and coral rubble=55.0%±13.2) due to mortality after 76h post-release.
KeywordsDispersal–Phototaxis–Metamorphosis–Recruitment–Porifera
Social Neuropeptides in Nematodes
The neuropeptides oxytocin and vasopressin stimulate maternal, reproductive, aggressive, and affiliative behaviors in mammals. They are implicated in behaviors ranging from ewe-lamb bonding in sheep to pair bonding in voles (see the Perspective by Emmons ). Now, Garrison et al. (p. 540 ) and Beets et al. (p. 543 ) extend the evolutionary reach of these social neuropeptides to the invertebrate nematode worm, Caenorhabditis elegans . A similar neuropeptide was found to function in mating and also to modulate salt-taste preference, based on prior experience, suggesting an ancient role in associative learning.
The nematode worm Caenorhabditis elegans can learn and remember the stimuli it encounters, the environment it is in, and its own physiological state. Analyses of mutations in C. elegans that affect different aspects of experience are beginning to address the nature of learning.
The cyclic nonapeptides, oxytocin and vasopressin, are neurohypophysial hormones that regulate many significant physiological processes related especially to reproduction and osmoregulation. In this study, we characterized an oxytocin-related peptide cDNA from a urochordate, Styela plicata, thought to be a sister group to vertebrates. Sequence analysis of the deduced precursor polypeptide revealed that the precursor is composed of three segments: a signal peptide, an oxytocin-like sequence flanked by a Gly C-terminal amidation signal and a Lys-Arg dibasic processing site, and a neurophysin domain, similar to other oxytocin/vasopressin family precursors. However, unlike other members of this family, the tunicate oxytocin-like peptide (CYISDCPNSRFWST-NH2) is a tetradecapeptide. We termed this peptide Styela oxytocin-related peptide (SOP). Furthermore, analyses of mass spectrometry, in situ hybridization, and immunohistochemistry demonstrated production of mature SOP in the cerebral ganglion. To elucidate the physiological action of SOP, we kept the tunicate for 2 d under the three different concentrations of seawater, 60, 100, and 130%, and measured the expression levels of SOP mRNA in the cerebral ganglion. The greatest expression of SOP mRNA was observed in the 60% seawater. In 60% seawater, but not in 100 or 130%, the tunicate mostly closed the atrial and branchial siphons. Therefore, we investigated the contractile effects of SOP on the siphons in vitro. SOP caused contractions in both siphons in a dose-dependent manner. Taken together, these results suggest that SOP acts to prevent the influx of a low concentration of seawater into the body and thus play an important role in osmoregulation.