Sea Star Species Research Articles

New Polyhydroxysteroid Glycosides with Antioxidant Activity from the Far Eastern Sea Star Ceramaster patagonicus.

Four new glycosides of polyhydroxysteroids, ceramasterosides A, B, D, and E (1-4), and two previously known compounds, ceramasteroside C1 (5) and attenuatoside B-I (6), were isolated from an extract of a deep-sea sea star species, the orange cookie star Ceramaster patagonicus. The structures of 1-4 were elucidated by the extensive NMR and ESIMS methods. Steroid monoglycosides 1 and 2 had a common 3β,6α,8,15β,16β-pentahydroxysteroid nucleus and a C-29 oxidized stigmastane side chain and differed from each other only in monosaccharide residues. Ceramasteroside A (1) contained 3-O-methyl-4-O-sulfated β-D-xylopyranose, while ceramasteroside B (2) had 3-O-methyl-4-O-sulfated β-D-glucopyranose, recorded from starfish-derived steroid glycosides for the first time. Their biological activity was studied using a model of lipopolysaccharide-induced (LPS) inflammation in a SIM-A9 murine microglial cell line. During the LPS-induced activation of microglial cells, 1, 3, and 5, at a non-toxic concentration of 1 µM, showed the highest efficiency in reducing the production of intracellular NO, while 4 proved to be most efficient in reducing the extracellular nitrite production. All the test compounds reduced the LPS-induced malondialdehyde (MDA) production. The in vitro experiments have demonstrated, for the first time, the antioxidant activity of the compounds under study.

Keanekaragaman dan Kelimpahan Bintang Laut Di Daerah Pesisir Dusun Pandanan, Kecamatan Sekotong Barat, Kabupaten Lombok Barat

Sea stars have morphological characteristics that are radially symmetrical, have 5 (five) or more arms, do not have a skeleton and move freely using tube legs. Sea stars not only function as litter cleaners in the waters, but are also utilized as food processing and handicraft materials. The study aimed to determine the diversity and abundance of sea star species in the coastal area of Pandanan Hamlet, West Sekotong, West Lombok Regency. This study used the belt transect method. All starfish found in the transect recorded the type, number, and habitat characteristics. The results found 6 species of starfish from 4 families namely Echinasteridae, Archasteridae, Ophidiasteridae, and Oreasteridae. The six species are Henricia sp., Archaster typicus, Linckia laevigata, Culcita sp., and Pentaceraster sp. The diversity index (H') has a value of 0.3 - 1.7, the uniformity index (E) is 0.5 - 0.9, and the dominance index (C) ranges from 0.2 - 0.8. The highest abundance in the species Linckia laevigata with a value of 571 ind/ha (station 1) and 333 ind/ha (station 1), while the lowest abundance in the species Pentaceraster sp. 33 ind/ha. All starfish were found to be associated with seagrass plants except Pentaceraster sp.

Larval development of Holothuria tubulosa, a new tractable system for evo-devo

To explore animal diversity, new experimentally tractable organisms must be established. Echinoderms include five groups of marine animals that have been used as developmental models for over a century thanks to their low costs, high fecundity, optically clear larvae and genetic tractability. An additional advantage of echinoderms is that their larval forms display diverse morphologies. This rich diversity enables comparative studies to investigate the evolutionary relationships among cell types, tissues, and organs. However, reproducible protocols to obtain gametes, detailed information on embryogenesis, and genomic tools have been optimized only for selected species of sea urchins and sea stars. To address this gap, we established the abundant Mediterranean sea cucumber Holothuria tubulosa as a new experimental system. Here we describe a method to reliably obtain gametes and make embryonic cultures multiple times from the same animal and characterize unique larval tissues combining immunohistochemistry and high-resolution microscopy. This work represents a step forward in our understanding of holothurian development and establishes H. tubulosa as an emerging experimental system for evo-devo and other biological disciplines.

Noble hosts: effects of internal parasites on the physiology of an intertidal brooding Sea-star

Introduction: The endoparasite Dendrogaster argentinensis infects the intertidal brooder sea star Anasterias antarctica. This sea-star species is in the highest trophic level in the Beagle Channel.
 Objective: To study the effects of parasitism by D. argentinensis on the fitness and reproduction of A. antarctica.
 Methods: Adults from the brooder sea-star were collected from the rocky intertidal of Ensenada Zaratiegui bay (54°51’ S & 68°29’ W), Argentina. Eight seasonal samplings were performed (four seasons in two years) in the upper and low intertidal. During dissection, parasites were removed, and all organs were extracted and weighed separately.
 Results: Dendrogaster argentinensis prevalence was the highest for the region (20.4 %). Parasitized individuals were more frequent in the low intertidal in all seasons, with a higher difference in summer, where it is likely that the higher temperatures and strong winds could make the upper intertidal more challenging for a parasitized individual. Five parasitized individuals were castrated. Generally, the gonadal (GI) and somatic (pyloric caeca, PCI; stomach, SI; body wall, WI) indexes were lower in parasitized than non-parasitized individuals.
 Conclusions: Parasitism by D. argentinensis negatively affects A. antarctica condition. It affects reproduction because it reduces the GI, and can also produce castration. The parasite competes for the sea-stars’ energetic resources, also decreasing the individual’s capacity for feeding (reduced stomach) and growth (reduced body wall).

An open‐source general purpose machine learning framework for individual animal re‐identification using few‐shot learning

Abstract Animal re‐identification remains a challenging problem due to the cost of tagging systems and the difficulty of permanently attaching a physical marker to some animals, such as sea stars. Due to these challenges, photo identification is a good fit to solve this problem whether evaluated by humans or through machine learning. Accurate machine learning methods are an improvement over manual identification as they are capable of evaluating a large number of images automatically and recent advances have reduced the need for large training datasets. This study aimed to create an accurate, robust, general purpose machine learning framework for individual animal re‐identification using images both from publicly available data as well as two groups of sea stars of different species under human care. Open‐source code was provided to accelerate work in this space. Images of two species of sea star (Asterias rubens and Anthenea australiae) were taken using a consumer‐grade smartphone camera and used as original datasets to train a machine learning model to re‐identify an individual animal using few examples. The model's performance was evaluated on these original sea star datasets which contained between 39–54 individuals and 983–1204 images, as well as using six publicly available re‐identification datasets for tigers, beef cattle noses, chimpanzee faces, zebras, giraffes and ringed seals ranging between 45–2056 individuals and 829–6770 images. Using time aware‐splits, which are a data splitting technique ensuring that the model only sees an individual's images from a previous collection event during training to avoid information leaking, the model achieved high (>99%) individual re‐identification mean average precision for the top prediction (mAP@1) for the two species of sea stars. The re‐identification mAP@1 for the mammalian datasets was more variable, ranging from 83% to >99%. However, this model outperformed published state‐of‐the‐art re‐identification results for the publicly available datasets. The reported approach for animal re‐identification is generalizable, with the same machine learning framework achieving good performance in two distinct species of sea stars with different physical attributes, as well as seven different mammalian species. This demonstrates that this methodology can be applied to nearly any species where individual re‐identification is required. This study presents a precise, practical, non‐invasive approach to animal re‐identification using only basic image collection methods.

Xyloplax princealberti (Asteroidea, Echinodermata): A New Species That Is Not Always Associated with Wood Falls

Xyloplax is a genus of three species of sea stars previously found only on sunken wood in the deep ocean. Their circular and petaloid bodies, which lend them their common name “sea daisy”, and their presumed exclusive diet of wood make them an unusual and rare element of deep-sea ecosystems. We describe here the fourth species of Xyloplax from the eastern Pacific Ocean, Xyloplax princealberti n. sp., which ranges from offshore Canada to the Gulf of California (Mexico) and Costa Rica. Though sampled geographically close to another described species of Xyloplax from the northeastern Pacific, X. janetae, this new species is unique morphologically and according to available DNA data. The short abactinal spines are the most obvious feature that distinguishes X. princealberti n. sp. from other Xyloplax. The minimum distance for mitochondrial cytochrome c oxidase subunit I from Xyloplax princealberti n. sp. to the only other available Xyloplax, X. janetae, was 13.5%. We also describe Ridgeia vestimentiferan tubeworm bushes from active hydrothermal vents as a new Xyloplax habitat, the first record of a non-wood substrate, and a new reproductive strategy, simultaneous hermaphroditism, for this genus. We generated the first mitochondrial genome for a member of Xyloplax and analyzed it with other available asteroid data using nucleotide-coding or amino acid (for protein-coding genes) plus nucleotide coding (for rRNA genes). The nucleotide-coding results place Xylopax as part of the clade Velatida, consistent with a previous phylogenomic analysis that included Xyloplax princealberti n. sp. (as Xyloplax sp.), though the placement of Velatida within Asteroidea differed. The amino acid plus nucleotide coding recovered Velatida to be a grade with X. princealberti n. sp. as sister group to all other Asteroidea.

Conservation and contrast in cell states of echinoderm ovaries.

Echinoderms produce functional gametes throughout their lifespan, in some cases exceeding 200 years. The histology and ultrastructure of echinoderm ovaries has been described but how these ovaries function and maintain the production of high-quality gametes remainsa mystery. Here, we present the first single cell RNA sequencingdata sets of mature ovaries from two sea urchin species (Strongylocentrotus purpuratus [Sp] and Lytechinus variegatus [Lv]), and one sea star species (Patiria miniata [Pm]). We find 14 cell states in the Sp ovary, 16 cell states in the Lv ovary and 13 cell states in the ovary of the sea star. This resource is essential to understand the structure and functional biology of the ovary in echinoderms, and better informs decisions in the utilization of in situ RNAhybridization probes selective for various cell types. We link key genes with cell clusters in validation of this approach. This resource also aids in the identification of the stem cells for prolonged and continuous gamete production, is a foundation for testing changes in the annual reproductive cycle, and is essential for understanding the evolution of reproduction of this important phylum.

Evidence of introgression, ecological divergence and adaptation in Asterias sea stars.

Hybrid zones are important windows into the evolutionary dynamics of populations, revealing how processes like introgression and adaptation structure population genomic variation. Importantly, they are useful for understanding speciation and how species respond to their environments. Here, we investigate two closely related sea star species, Asterias rubens and A. forbesi, distributed along rocky European and North American coastlines of the North Atlantic, and use genome-wide molecular markers to infer the distribution of genomic variation within and between species in this group. Using genomic data and environmental niche modelling, we document hybridization occurring between northern New England and the southern Canadian Maritimes. We investigate the factors that maintain this hybrid zone, as well as the environmental variables that putatively drive selection within and between species. We find that the two species differ in their environmental niche breadth; Asterias forbesi displays a relatively narrow environmental niche while conversely, A. rubens has a wider niche breadth. Species distribution models accurately predict hybrids to occur within environmental niche overlap, thereby suggesting environmental selection plays an important role in the maintenance of the hybrid zone. Our results imply that the distribution of genomic variation in North Atlantic sea stars is influenced by the environment, which will be crucial to consider as the climate changes.

Zenopontonia soror caridean shrimp exhibits dynamical mimicry with sea star host switching

Zenopontonia soror (Nobili, 1904) (Caridea: Palaemonidae) is a shrimp symbiont of several sea star species that exhibits homochromy with distinct mimetic coloration according to host species. To date, populations of Z. soror have been studied extensively in the Indo-Pacific and Gulf of Panama; however, those present in the Gulf of California (Mexico) have not been evaluated. Here we conduct the first evaluation of the diversity of chromotypes present in Z. soror populations in Bahía de La Paz (Baja California Sur, Mexico), and experimentally tested how long shrimp take to archieve mimicry post sea star switch. We hypothesized that Z. soror individuals rapidly change coloration (minutes to few hours) throughout their ontogeny to mimic the coloration of host species to decrease risk of predation. This hypothesis was tested by translocating Z. soror individuals to a different sea star species with different coloration and background in the field and under laboratory conditions for three consecutive days. At least 18 chromotypes of Z. soror were identified among 386 observed specimens based on the RGB color system; and colors were independent of body size. Each chromotype holds different relative abundance in the population. Coloration was not distinctive of each individual, while color intensity increased along ontogeny development from semi-transparent (juveniles) to solid coloration (adult phase). Dynamic contraction or dispersion of the chromatophores (pigment migration) caused changes in coloration to resemble coloration of the basibiont sea star. Full mimicry of new host was achieved within 36 h in field and laboratory conditions. Zenopontonia soror individuals were observed to mimic the white spines of the sea star host Acanthaster solaris by exhibiting a white dorsal band, while others selected color-concealing hosts to stay cryptic for a short time. We conclude that Z. soror dynamically shifts coloration as an adaptation to match the symbiont shrimp–sea star host coloration to minimize or prevent predation, but individuals are vulnerable to be detected by visual predators during the color transition (<36 h period). The combined use of the Hogben and Slome index and the RGB color system from digital images provide the most precise method to assign intensity and color in epibiont-host organisms to understand the complex process of homochromy.

Species-specific metabolites mediate host selection and larval recruitment of the symbiotic seastar shrimp

In marine environments, host selection, defining how symbiotic organisms recognize and interact with their hosts, is often mediated by olfactory communication. Although adult symbionts may select their hosts detecting chemosensory cues, no information is available concerning the recruitment of symbiotic larvae which is a crucial step to sustain symbioses over generations. This study investigates the olfactory recognition of seastar hosts by adult Zenopontoniasoror shrimps and the recruitment of their larvae. We examine the semiochemicals that influence host selection using chemical extractions, behavioural experiments in olfactometers, and mass spectrometry analyses. After describing the symbiotic population and the embryonic development of shrimps, our results demonstrate that asterosaponins, which are traditionally considered as chemical defences in seastars, are species-specific and play a role in attracting the symbiotic shrimps. Adult shrimps were found to be attracted only by their original host species Culcitanovaeguineae, while larvae were attracted by different species of seastars. This study provides the first chemical identification of an olfactory cue used by larvae of symbiotic organisms to locate their host for recruitment. These findings highlight the importance of chemical communication in the mediation of symbiotic associations, which has broader significant implications for understanding the ecological dynamics of marine ecosystems.

A Decade of Death and Other Dynamics: Deepening Perspectives on the Diversity and Distribution of Sea Stars and Wasting.

AbstractMass mortality events provide valuable insight into biological extremes and also ecological interactions more generally. The sea star wasting epidemic that began in 2013 catalyzed study of the microbiome, genetics, population dynamics, and community ecology of several high-profile species inhabiting the northeastern Pacific but exposed a dearth of information on the diversity, distributions, and impacts of sea star wasting for many lesser-known sea stars and a need for integration across scales. Here, we combine datasets from single-site to coast-wide studies, across time lines from weeks to decades, for 65 species. We evaluated the impacts of abiotic characteristics hypothetically associated with sea star wasting (sea surface temperature, pelagic primary productivity, upwelling wind forcing, wave exposure, freshwater runoff) and species characteristics (depth distribution, developmental mode, diet, habitat, reproductive period). We find that the 2010s sea star wasting outbreak clearly affected a little over a dozen species, primarily intertidal and shallow subtidal taxa, causing instantaneous wasting prevalence rates of 5%-80%. Despite the collapse of some populations within weeks, environmental and species variation protracted the outbreak, which lasted 2-3 years from onset until declining to chronic background rates of ∼2% sea star wasting prevalence. Recruitment began immediately in many species, and in general, sea star assemblages trended toward recovery; however, recovery was heterogeneous, and a marine heatwave in 2019 raised concerns of a second decline. The abiotic stressors most associated with the 2010s sea star wasting outbreak were elevated sea surface temperature and low wave exposure, as well as freshwater discharge in the north. However, detailed data speaking directly to the biological, ecological, and environmental cause(s) and consequences of the sea star wasting outbreak remain limited in scope, unavoidably retrospective, and perhaps always indeterminate. Redressing this shortfall for the future will require a broad spectrum of monitoring studies not less than the taxonomically broad cross-scale framework we have modeled in this synthesis.

Anti-predatory responses of two native gastropods to an invasive predator

As native prey species lack a co-evolutionary history with invasive predators, they often have limited capacity to identify and respond to the threat of predation. This phenomenon has led to the prey naivety hypothesis. Invasive predators can have devastating impacts on native prey populations. Thus, there is a need to better understand the ability of native species to respond to invasive predators. Here, laboratory behavioural experiments tested the anti-predatory responses of two gastropods, Cominella lineolata and Dicathais orbita, against an invasive predator, Asterias amurensis, and a native predator, Coscinasterias muricata. There was no chemical exudate released by any D. orbita to either species of seastar or a wax seastar control. Only a small percentage of D. orbita individuals fled from the invasive (12.5%) and native (17%) seastars. The overall separation distance between D. orbita and the two seastars was recorded for a further three minutes. While the measured distance between the invasive seastar and D. orbita was greater (61 ± 7 mm) than the distance between the native seastar (39 ± 10 mm), this was not statistically significant. In contrast, C. lineolata exhibited strong responses to the native seastar, but less strongly to the invasive seastar. Only 50% of snails fled and 15% released an exudate in response to A. amurensis, compared to 80% of snails fleeing and releasing an exudate to the native seastar. In contrast to expectations, C. lineolata collected from naïve populations tended to respond less frequently (25% of snails) by fleeing from the invasive seastar than snails collected from exposed (50% of snails), however this was not significant. This same trend was observed for C. muricata with 70% and 90% of snails fleeing from exposed and naïve populations, respectively. After recording the behavioural responses of both seastars and snails for three minutes, the release of exudate resulted in an increased separation distance between C. lineolata and C. muricata of 122 mm (± 31 mm) compared with just 28 mm (± 16 mm) when the snails failed to release the exudate, whereas the separation distances between C. lineolata and A. amurensis was 143 mm (± 31 mm) and 87 mm (± 10 mm) with and without exudate release, respectively. This latter result indicates that while the exudate appears to be an effective anti-predatory mechanism against the native seastar, it appears less effective against the invasive seastar.

Exploring the Effects of Varying Retinol Vitamin A Concentrations on Tissue Regeneration in the Species Asterina coronata

The following study will look at the relationship between tissue and regeneration rate in the sea star species Asterina and retinol vitamin A. The overall purpose of the study is to evaluate whether concentrations of retinol vitamin A will produce a positive, negative, or null effect on the tissue regeneration in Asterina coronata. After amputation of the ray, 48 sea stars were subjected to four different retinol vitamin A concentration levels for sixteen hours and observed over a thirty-to-forty-day time period. The results show that the second highest concentration group produced the most consistent and noticeable growth. Moreover, the highest concentration group showed the second highest rate compared with the lowest concentration group and the control. Through these results, it can be concluded that retinol vitamin A does support tissue regeneration in Asterina coronata to a limit before it begins a negative feedback. The findings in this study add to an understanding of the mechanisms behind cell differentiation and whether stem cells involving tissue regeneration can be activated with the treatment of vitamin A. Hopefully the connections made in this paper can impact current research on human stem cell therapy itself, and the topic of whether sea stars can be made into viable stem cell therapy models.

Antibacterial potential of Luidia clathrata (sea star) tissue extracts against selected pathogenic bacteria.

As resistance to traditional antibiotics has become a major issue, it is essential to explore natural sources for new antimicrobial agents. The marine environment offers a variety of natural bioactive compounds. In this study, we examined the antibacterial potential of Luidia clathrata, a tropical sea star species. The experiment was conducted against both gram-positive (Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus and Mycobacterium smegmatis) and gram-negative (Proteus mirabilis, Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae) bacteria using disk diffusion method. Specifically, we extracted the body wall and gonad using methanol, ethyl acetate, and hexane. Our findings show that the body wall extract using ethyl acetate (1.78μg/ml) was particularly effective against all tested pathogens, while the gonad extract (0.107μg/ml) showed activity against six out of ten selected pathogens. This is a crucial and new discovery that suggests L. clathrata may be a useful source for discovering antibiotics and more research is required to pinpoint and comprehend the active ingredients.

Prevalence of the scuticociliate Orchitophrya stellarum in seastars from the Pacific and Atlantic oceans

As part of a study to investigate the use of the scuticociliate Orchitophrya stellarum as a biological control for the invasive seastar Asterias amurensis in Australia, we collected prevalence data for O. stellarum from 3 seastar species (A. amurensis, A. rubens, Pisaster ochraceus) between 1996 and 1999 from the Pacific (Australia, Japan, Korea, Canada) and Atlantic (France, Netherlands, Canada) oceans. In the Pacific Ocean, for the first time, we found O. stellarum in male A. amurensis in Korea and female A. amurensis in Japan. The parasite was not detected in the invasive A. amurensis from Australia. There was no significant difference between size of infected and uninfected male seastars, nor a correlation between biased sex ratio and parasite prevalence in populations in the Pacific or Atlantic oceans. Therefore, unlike other studies, we found size and sex ratio in seastar populations in the field are unreliable indicators of parasite impacts. Regular monitoring of infected seastar populations in the field would be useful to better understand how sex ratio varies with parasite prevalence. We recommend laboratory studies under controlled conditions to determine the effect of O. stellarum on seastar populations.

Genetic population structure of the blue sea star (Linckia laevigata) and the boring giant clam (Tridacna crocea) across Malaysia

Various studies on population genetics in the Indo-Pacific that include the Coral Triangle region have revealed phylogeographic patterns in marine species populations. However, little is known about the population structure and connectivity pattern among the coral reefs in four seas surrounding Malaysia: the Strait of Malacca (Andaman Sea), the South China Sea, the Sulu Sea, and the Sulawesi Sea. In view of this, we examined the genetic population structure of two invertebrate species: the blue sea star (Linckia laevigata) and the boring clam (Tridacna crocea) from seven localities across Malaysia, including Pulau Layang-Layang in the Spratly Islands. Additional samples of L. laevigata were obtained from the Davao Gulf, the Philippines. The analyses were based on partial mitochondrial cytochrome oxidase I sequences of L. laevigata and T. crocea. Populations of L. laevigata and T. crocea showed departure from neutrality, indicating selection or population expansion. However, a mismatch analysis suggested population expansion. Lack of genetic population structure in L. laevigata (ΦST = − 0.001, P = 0.399) implies high connectivity among the sampled reef sites. There was subtle genetic structuring in populations of T. crocea (ΦST = 0.032, P = 0.009), but AMOVA did not detect any structure in the a priori groupings. The genetic population structure and scale in connectivity are most likely attributed to the life history traits of the sea star and giant clam species, and also to the geological history and seasonal current patterns of the region.

Comparison of swab DNA extraction methods for examining sea star dermal microbiomes

Marine invertebrates are surrounded by and interact with an array of microbes, yet their microbiomes remain largely unexplored. With a seemingly endless choice of nucleic acid extraction kits, there is a need to assess the compatibility across approaches to determine whether microbiome results are comparable across studies employing different extraction methods. In this study, 5 kits were compared for extracting DNA from dermal swabs from 2 sea star species: Pisaster ochraceus and Dermasterias imbricata. DNA yield varied by kit, as did the ease of PCR amplification. Using 16S rRNA amplicon sequencing, differences in microbial richness and diversity were observed between sea star species, but not among extraction kits. Relative abundances of the most abundant prokaryotic phyla were largely attributed to sea star species rather than kit: the D. imbricata microbiome was dominated by Proteobacteria, whereas P. ochraceous had more even representation of Proteobacteria, Spirochaetota and Bacteroidota. Our results suggest that, despite some differences in ease of amplification, all 5 extraction kits examined here provide comparable and suitable results for characterizing sea star dermal microbiomes.

Death of A Star

&#x0D; Sea star wasting disease (SSWD), originally identified in 2013, is an epidemic impacting 20 species of sea stars along the west coast of North America. Two of the most impacted species, Pisaster ochraceus and Pycnopodia helianthoides are keystone species. The loss of these sea stars impacts oceanic life. Literature reviews were conducted from January to May 2022 to investigate the effect of SSWD on the food web of sea stars and decline of kelp. The apex predators of the ecosystem, P. helianthoides and P. ochraceus, have decreased drastically, while their prey, urchins, have increased immensely. As a result, kelp, a producer, has decreased significantly. The decline of the keystone species is highly concerning and could have drastic ecological impacts. The loss of kelp is extremely damaging for both marine life and Earth itself. If sea stars continue to decline, the amount of carbon dioxide and loss of kelp will become increasingly problematic for the ocean and health of the planet.&#x0D;

Lineage tracing shows that cell size asymmetries predict the dorsoventral axis in the sea star embryo

BackgroundCell size asymmetries are often linked to cell fate decisions, due to cell volumes and cell fate determinants being unequally partitioned during asymmetric cell divisions. A clear example is found in the sea urchin embryo, where a characteristic and obvious unequal 4th cleavage generates micromeres, which are necessary for mesendoderm cell fate specification. Unlike sea urchin development, sea star development is generally thought to have only equal cleavage. However, subtle cell size asymmetries can be observed in sea star embryos; whether those cell size asymmetries are consistently produced during sea star development and if they are involved in cell fate decisions remains unknown.ResultsUsing confocal live imaging of early embryos we quantified cell size asymmetries in 16-cell stage embryos of two sea star species, Patiria miniata and Patiriella regularis. Using photoconversion to perform lineage tracing, we find that the position of the smallest cells of P. miniata embryos is biased toward anterior ventral tissues. However, both blastomere dissociation and mechanical removal of one small cell do not prevent dorsoventral (DV) axis formation, suggesting that embryos compensate for the loss of those cells and that asymmetrical partitioning of maternal determinants is not strictly necessary for DV patterning. Finally, we show that manipulating cell size to introduce artificial cell size asymmetries is not sufficient to direct the positioning of the future DV axis in P. miniata embryos.ConclusionsOur results show that although cell size asymmetries are consistently produced during sea star early cleavage and are predictive of the DV axis, they are not necessary to instruct DV axis formation.

A Review of Asteroid Biology in the Context of Sea Star Wasting: Possible Causes and Consequences.

AbstractSea star wasting-marked in a variety of sea star species as varying degrees of skin lesions followed by disintegration-recently caused one of the largest marine die-offs ever recorded on the west coast of North America, killing billions of sea stars. Despite the important ramifications this mortality had for coastal benthic ecosystems, such as increased abundance of prey, little is known about the causes of the disease or the mechanisms of its progression. Although there have been studies indicating a range of causal mechanisms, including viruses and environmental effects, the broad spatial and depth range of affected populations leaves many questions remaining about either infectious or non-infectious mechanisms. Wasting appears to start with degradation of mutable connective tissue in the body wall, leading to disintegration of the epidermis. Here, we briefly review basic sea star biology in the context of sea star wasting and present our current knowledge and hypotheses related to the symptoms, the microbiome, the viruses, and the associated environmental stressors. We also highlight throughout the article knowledge gaps and the data needed to better understand sea star wasting mechanistically, its causes, and potential management.