All attempts to determine the mechanism of contractions and signal propagation in other sponges, including bath application of chemicals, substitution of ions in the medium and triggering with mechanical and electrical stimuli, so far show that electrical signalling does not occur in cellular sponges. Capture of prey would be best achieved by filtration and concentration of food, which favours the idea of a filter/suspension feeder arising before the evolution of complex nervous systems. It also seems to be the main organ for sensing stimuli from the environment and triggering responses by the whole animal. Glass sponges can contract but very slowly (Nickel, 2010), and contraction may not be effective to prevent damage by a sudden resuspension event. Also, there are more distinctive difference between the sexes i… The baby sponge floats freely in the water for weeks or months before settling down and developing into an adult sponge. The fact that cilia appear at the osculum of all sponges studied so far (even hexactinellids), suggests that this is a common sensory organ in Porifera. With no life yet on land, bacteria-rich seas fertilized by aggregates of faeces would not have existed and without that it is unlikely there would have been high levels of dissolved organic carbon (DOC). Propagation across a whole animal can take 30 min to 1 h, so a signal cascade via metabotropic glutamate receptors (mGluRs), which binds glutamate via a GPCR is expected to be sufficiently rapid for transmitting signals between cells. What Are the Main Characteristics of Echinodermata? Storytelling. The sponge must therefore filter any particles that are in the water around it, including inorganic detritus such as fine sediments disturbed by fish or storms. The attractiveness of this model, which was highlighted by Yoko Watanabe through the film ‘Life of the freshwater sponge’ (Tokyo Film Corporation, has led to more recent studies on signalling and coordination of sponge behaviour (Elliott and Leys, 2007; Elliott and Leys, 2010), epithelia (Leys et al., 2009; Adams, 2010), patterning (Windsor and Leys, 2010) and most recently, sensory cells (Ludeman et al., 2014). 4. Larval behaviour is the other main activity known from sponges: larvae change swimming direction within seconds of a change in light intensity, some in response to gravity and other stimuli (reviewed in Maldonado and Bergquist, 2002). It is possible that some of these molecules are so divergent that they remain undetected with BLAST searches. 4C) (Leys and Mackie, 1997). Thank you for your interest in spreading the word on Journal of Experimental Biology. The characteristics of glass sponge conduction are as follows. Sponges don’t have tissues and organs. The simplest explanation for the ‘steering’ of the larva is that each cell responds independently to changes in light intensity as the larva rotates through the water (Leys and Degnan, 2001). There is published work on the physiology (Lentz, 1966) and recently also the molecular biology (Leininger et al., 2014) of Sycon, a genus of calcareous sponge. And they do it with an energy that’s almost like a The photo pigment in the Amphimedon queenslandica larva has been studied more closely and is thought to be a cryptochrome with sensitivity at around 450 nm (Leys et al., 2002). Our understanding of the sensory role of primary cilia in animals and unicellular flagellates such as Chlamydomonas comes from behavioural assays (Fujiu et al., 2011). Ctenophora (/ t ɪ ˈ n ɒ f ər ə /; singular ctenophore, / ˈ t ɛ n ə f ɔːr / or / ˈ t iː n ə f ɔːr /; from Ancient Greek: κτείς, romanized: kteis, lit. Potassium channels are responsible for stabilizing membrane potential, and so are indicators of electrical behaviour. Now that the children have gained more knowledge from the two weeks of lesson plans, they might be able to relate to the story a bit more because they know what the information really means about the different senses the body uses to gather information. Therefore, this animal would most likely have evolved in shallow waters in competition with other flagellates and have specialized to be efficient at filtering. Ion channels are responsible for all rapid ionic changes across membranes. In Tethya wilhelma, for example, a sieve-like cell (sometimes two) forms the apopyle or excurrent passage of chambers and this cell expresses genes for myosin (Steinmetz et al., 2012). Photos: R. dawsoni, S. coactum, O. minuta, E. muelleri, T. wilhelma, A. queenslandica, S. Leys; O. carmella courtesy of S. Nichols; O. lobularis reprinted with permission from Van Soest et al. Phylum Porifera – … Furthermore, neomycin sulphate, FM 1-43 and gadolinium all reduce or block the ability of the sponge to carry out a ‘sneeze’ and the effect is reversible (Ludeman et al., 2014). Their simple anatomy is similar to that of the earliest members of the animal kingdom. Syncytial tissues allow electrical signals to travel unimpeded by membrane barriers throughout the whole animal and these cause the feeding current to stop within seconds of a mechanical or electrical stimulus; the effect is ‘all or none’ (Leys and Mackie, 1997). In glass sponges the syncytial tissues transmit electrical signals, and the effectors are the flagella of choanocytes, which stop beating. for coordinating developmental processes in sperm or in the embryo). © 2020 WILD SKY MEDIA. Here, I examine the elements of the sponge neural toolkit including sensory cells, conduction pathways, signalling molecules and the ionic basis of signalling. discuss oxygen-sensing systems across both plants and animals and argue that the systems are functionally convergent and … 7 in Leys and Meech (Leys and Meech, 2006)]. 2J) (Leys and Degnan, 2001; Maldonado et al., 2003). If filtration was the mechanism of feeding, it may have been energetically expensive (Leys et al., 2011), so it is unlikely to have originated in deep oxygen-poor oceans. Dogs and humans have very similar social systems. The better they anticipated our thoughts and feelings, the more they were rewarded with food, shelter a… Because of the large volumes of water they filter, unless water exchange is great, waste products quickly build up. I Histology of, Choanoflagellate and choanocyte collar-flagellar systems and the assumption of homology, The cellular basis of photobehavior in the tufted parenchymella larva of demosponges, Nutrient fluxes through sponges: biology, budgets, and ecological implications, Possible animal-body fossils in pre-Marinoan limestones from South Australia, Motor reactions of the fresh-water sponge, Phylogenie und evolutionsökologie der hexactinellida (Porifera) im paläozoikum, Phylogenetic analysis of freshwater sponges provide evidence for endemism and radiation in ancient lakes, Toward understanding the morphogenesis of siliceous spicules in freshwater sponge: differential mRNA expression of spicule-type-specific silicatein genes in, On the independent origins of complex brains and neurons, The ctenophore genome and the evolutionary origins of neural systems, A calcium regenerative potential controlling ciliary reversal is propagated along the length of ctenophore comb plates, Growth and reproduction of four species of freshwater sponge cultured in their natural surroundings, Further studies on growth and sex differentiation in four species of freshwater sponges, Differential expression of the demosponge (, Kinetics and rhythm of body contractions in the sponge. This means they don't have eyes, ears or the ability to physically feel anything. However, Earth's atmosphere has not always contained such high oxygen concentrations. Evidence for glutamate, GABA and NO in coordinating behaviour in the sponge, Sponge larval phototaxis: a comparative study, Bollettino dei Musei e degli Istituti Biologici dell'Università di Genova, Neuroactive substances specifically modulate rhythmic body contractions in the nerveless metazoon, Glutamate, GABA and serotonin induce contractions in the sponge, Zoologisches Institut der Universität Rostock, GABA and glutamate specifically induce contractions in the sponge, Metazoan opsin evolution reveals a simple route to animal vision, The ultrastructure of choanocyte collars in, Genome-wide analysis of the sox family in the calcareous sponge, Electrical signals and their physiological significance in plants, The stem cell system in demosponges: suggested involvement of two types of cells: archeocytes (active stem cells) and choanocytes (food-entrapping flagellated cells). Importantly, Prosser showed that contractions can occur at 10-fold higher external potassium concentrations (100 mmol l−1), which would normally depolarize cells, so he concluded it was unlikely that action potentials were involved in contractions (Prosser, 1967). Peptidergic signalling plays a large role in ctenophore and cnidarian nervous systems (Anctil, 1987; Spencer, 1989), but sponges could use peptides as signalling molecules even without nerves. This work was presented at the ‘Evolution of the First Nervous Systems II’ meeting, which was supported by the National Science Foundation (NSF). Understanding that sponges have ‘tissues’, which are groups of cells that are organized together to carry out a particular function - is essential to be able to consider and interpret evidence of the function of neural-like elements. permollis (Leys, 1995). (C) Adherent aggregates fusing with the syncytial tissue of R. dawsoni, a preparation that allows extracellular recording from the sponge. The pigment inclusions are intracellular, and appear to lie in a cell adjacent to the ciliated sensory cell (Fig. The absorbent mind makes our adult lives possible. A suite of papers describing the morphology and development of canals, choanocytes and spicules established this as an easy-to-use system (Weissenfels, 1976; Weissenfels and Landschoff, 1977; Weissenfels and Striegler, 1979; Weissenfels, 1980; Weissenfels, 1981; Weissenfels and Hündgen, 1981; Weissenfels, 1982; Weissenfels, 1983; Weissenfels, 1984; Wachtmann et al., 1990; Weissenfels et al., 1990; Weissenfels, 1992). could pass current to one another in the presence of calcium and magnesium, suggesting that something like a gap junction exists in these cells, but the work has never been repeated. ALL RIGHTS RESERVED. In short, the two systems are not easily compared. Oddly, many papers report serotonin or serotonin-like molecules (brominated cyclodipetides) in chemical extracts from sponges (e.g. Sponge larvae show phototaxis and geotaxis (Maldonado and Bergquist, 2002).Where phototaxis has been studied in depth, directional swimming has been shown to occur by a combination of rotation of the larva around its anterior–posterior (A–P) axis and the shading by pigment of a Alternatively, is the presence in genomes, and even expression in tissues, of ‘neuronal’ genes in sponges enough to even warrant the label ‘pre-nervous system’? are expressed in globular cells of the epithelium of the larva of Amphimedon queenslandica, which are interpreted to be potential sensory cells receiving signal cues that guide settlement behaviour (Sakaraya et al., 2007; Richards et al., 2008). Higher concentrations caused such a vigorous contraction that the top of the sponge tore, although the canals continued through their full inflation and contraction. Studies on hexactinellid sponges. Amphiblastula larvae of calcareous sponges show negative phototaxis (Elliott et al., 2004) and have curious ‘cross cells’ which express Smad1/5 (Leininger et al., 2014) as well as SoxB (Fortunato et al., 2012), genes that are also expressed in vertebrate sensory systems. A temperature- and mechano-sensitive cation channel has been found in Axinella polypoides, but it is not known to have a role in directional signalling or coordination of behaviour (Zocchi et al., 2001). The fossil record does not give any insight into early ctenophore body plans – except for the idea that frond-like animals of the Ediacaran may have had ctenophoran affinities (Dzik, 2002) – but if ctenophores were predatory as extant species are, then what would they have eaten? The sponge genomic ‘toolkit’ either reflects a simple, pre-neural system used to protect the sponge filter or represents the remnants of a more complex signalling system and sponges have lost cell types, tissues and regionalization to suit their current suspension-feeding habit. 3A). In glass sponges, electrical signalling is by action potentials which travel via syncytia and also prevent damage to feeding chambers. Both Prosser (Prosser, 1967) and Adams et al. 3B,C) (Elliott and Leys, 2007). Some researchers compare the process to sneezing, since the water and inedible matter is expelled through a rapid bodily contraction throughout the sponge. Sponges are unique members of the animal kingdom. Sponge larvae settle and metamorphose more rapidly in the presence of GLW-amide peptides (Whalan et al., 2012), so peptides may be used by sponge larva for locating the right settlement substrate. The Kir channel isolated from Amphimedon shows rapid inactivation, which indicates that the channel resets the membrane potential quickly – as though it might respond to depolarization, a hint that electrical signalling may occur in Amphimedon (Tompkins-MacDonald et al., 2009). There is evidence for slow signalling in cellular sponges, probably using metabotropic receptors and calcium waves, which are slow, but effective at closing the intake system to prevent damage to feeding chambers and sufficiently fast to eject inedible material that may have entered and clogged chambers. The most obvious tissue of a sponge is the epithelium, which has the sensory cells and is thought to be the conducting pathway. region of cilia (Fig. Glass sponges form cellular embryos, which become syncytial after the 64-cell stage (6th cleavage) by fusion of macromeres (Leys et al., 2006). Or do we just want to believe these dolphin myths because they're so darn cute? Tethya wilhelma lives easily in aquaria and has an interesting contraction behaviour (Nickel 2001; Nickel, 2004). ‘Systems’ and ‘pathways’ are terms that typically refer to a constant morphological structure: tissues. The absolute refractory period, the period during which a second AP cannot be generated, is 29 s. The second of a pair of APs with delays between 30 s and 150 s have a lower amplitude and slower conduction velocity, indicating that 150 s is the relative refractory period (Fig. (B) Contraction of the osculum (left) and choanosomal region with feeding chambers (right) of Ephydatia muelleri with tracings showing the time of both events below. The elements described do not fit the scheme of a loss of sophistication, but seem rather to reflect an early specialization for suspension feeding, which fits with the presumed ecological framework in which the first animals evolved. Sponges are animals that belong to the phylum Porifera, which means "pore bearer." Scale bars: 20 μm (B); 1 mm (C). The five senses – scent, taste, sight, touch and hearing – are important tools for survival for humans and animals alike. Could the cost of filtering in the deep sea have triggered the evolution of syncytia concurrent with electrical signalling as a way to prevent intake of materials that might damage the filter? In an attempt to address these questions, I first briefly describe the nature of species from which data derives and then evaluate whether what we now know of the molecules, tissues and physiology of sponges best reflects elements of a potential (pre)nervous system, loss of one, or elements of a distinct system specialized for non-neural functions. (Rossellidae), Ecological regulation of development: induction of marine invertebrate metamorphosis, Conference presentation, World Sponge Conference, Developmental gene expression provides clues to relationships between sponge and eumetazoan body plans, Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era, Histochemical localization of neurohumors in a sponge, Fine structures of sponge cell membranes: comparative study with freeze-fracture and conventional thin section methods, Cytoskeletal architecture and organelle transport in giant syncytia formed by fusion of hexactinellid sponge tissues, Cytological basis of photoresponsive behavior in a sponge larva, Embryogenesis and metamorphosis in a haplosclerid demosponge: gastrulation and transdifferentiation of larval ciliated cells to choanocytes, Nutrient transport pathways in the neotropical sponge, The sponge pump: the role of current induced flow in the design of the sponge body plan, Evolutionary origins of sensation in metazoans: functional evidence for a new sensory organ in sponges, Conduction in the nerve-free epithelia of siphonophores, Neuroid conduction and the evolution of conducting tissues. (J) Response of the long posterior cilia in A. queenslandica to changes in light intensity: (I) bent when suddenly dark and (II) straightened when suddenly light (from Leys et al., 2002). A full ‘sneeze’ is triggered by 75 μmol l−1 l-Glu; lower concentrations generate localized contractions and higher concentrations cause the surface of the sponge to tear, whereas the canals continue a full inflation–contraction event (from Elliott and Leys, 2010). Are dolphins really that smart? Larvae have other sensory needs, which are attuned to helping them find the best settlement sites, but even these are morphologically simple compared with those of Cnidaria or Ctenophora. The very different phylogenetic hypotheses under discussion today suggest very different scenarios for the evolution of tissues and coordination systems in early animals. Anti-serotonin immunoreactivity was suggested for a sponge larva, but distribution of the label was difficult to associate with any particular cell or cells, and specificity of the antibody was not confirmed by western blotting (Weyrer et al., 1999). Gert Wörheide, an evolution expert of sponges … 2G,H). Top traces, electrical records; bottom traces, thermistor flow records: (i) a single stimulus causes and AP and arrest of flow; (ii,iii) repeated stimuli cause further APs even though the flow is still arrested; (iv) after pumping resumes a second stimulus causes a second AP and arrests the flow again. These experiments suggested that clogging of chambers with dye must trigger stretch receptors or reduce flow enough to make the sensory cells in the osculum (Ludeman et al., 2014) respond and cause the osculum to contract; the hypothesis is that glutamate receptors lie at the base of the osculum and along the entire epithelium of the sponge incurrent canal system. Solid line (both panels): ASW control. I thank members of my research group, in particular N. Farrar, A. Kahn and J. Mah, and my colleague J. Paps (Oxford University) for stimulating discussions that helped formulate the ideas presented in this paper. 4A). Recent work has referred to them as actinocytes and there is some evidence that actinocytes are largely epithelial, i.e. Many molecules are known to trigger contractions of the osculum, ostia or whole body of sponges (Emson, 1966; Prosser, 1967; Ellwanger et al., 2004; Ellwanger and Nickel, 2006). These cells are equipped with small tentacles called flagellae that whip back and forth to pull water into the sponge's body. Ongoing work by A. Kahn (Kahn and Leys, 2013) on the energetics of filtration promises new data on this question. The sum of knowledge of sponge coordination systems shows that sponges are largely epithelial animals, with sensory cells that are epithelial, effectors that are contractile epithelial cells as well as flagellated collar bodies lining the feeding chambers of glass sponges; signalling pathways also seem to use the epithelia. ). NF-κB (Gauthier and Degnan, 2008); bHLH and Delta (Richards et al., 2008); Frizzled (Adamska et al., 2010); TIRs (Gauthier et al., 2010)] so experimental work is needed to determine whether the gene expression is linked to sensory function. The next step would have involved innovation of more agile movement, including muscle and signalling systems (possibly epithelial); these body plans may have co-opted the elements found in sponges but would have required more sophisticated gene regulatory networks (Peter and Davidson, 2011) to build. This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Nevertheless, if sponges use peptidergic signalling, larval cells would be the place to look for receptors. But even for those that can be kept in tanks, few species release gametes (most of them brood embryos) and spawning events are usually unpredictable; only one, Tetilla serica (Watanabe, 1978) is known to have reproduced in captivity. Earlier workers identified the effectors of contractions in sponges as a type of smooth muscle cell called a myocyte (Bagby, 1966; Prosser, 1967); it was thought that these could be both in the mesohyl and epithelium.
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