Holothuria Leucospilota Research Articles

The interplay between host-specificity and habitat-filtering influences sea cucumber microbiota across an environmental gradient of pollution

Environmental gradients can influence morpho-physiological and life-history differences in natural populations. It is unclear, however, to what extent such gradients can also modulate phenotypic differences in other organismal characteristics such as the structure and function of host-associated microbial communities. In this work, we addressed this question by assessing intra-specific variation in the diversity, structure and function of environmental-associated (sediment and water) and animal-associated (skin and gut) microbiota along an environmental gradient of pollution in one of the most urbanized coastal areas in the world. Using the tropical sea cucumber Holothuria leucospilota, we tested the interplay between deterministic (e.g., environmental/host filtering) and stochastic (e.g., random microbial dispersal) processes underpinning host-microbiome interactions and microbial assemblages. Overall, our results indicate that microbial communities are complex and vary in structure and function between the environment and the animal hosts. However, these differences are modulated by the level of pollution across the gradient with marked clines in alpha and beta diversity. Yet, such clines and overall differences showed opposite directions when comparing environmental- and animal-associated microbial communities. In the sea cucumbers, intrinsic characteristics (e.g., body compartments, biochemistry composition, immune systems), may underpin the observed intra-individual differences in the associated microbiomes, and their divergence from the environmental source. Such regulation favours specific microbial functional pathways that may play an important role in the survival and physiology of the animal host, particularly in high polluted areas. These findings suggest that the interplay between both, environmental and host filtering underpins microbial community assembly in H. leucospilota along the pollution gradient in Hong Kong.

Sea cucumbers and their symbiotic microbiome have evolved to feed on seabed sediments

Sea cucumbers are predominant deposit feeders in benthic ecosystems, providing protective benefits to coral reefs by reducing disease prevalence. However, how they receive sufficient nutrition from seabed sediments remains poorly understood. Here, we investigate Holothuria leucospilota, an ecologically significant tropical sea cucumber, to elucidate digestive mechanisms underlying marine deposit-feeding. Genomic analysis reveals intriguing evolutionary adaptation characterized by an expansion of digestive carbohydrase genes and a contraction of digestive protease genes, suggesting specialization in digesting microalgae. Developmentally, two pivotal dietary shifts, namely, from endogenous nutrition to planktonic feeding, and from planktonic feeding to deposit feeding, induce changes in digestive tract enzyme profiles, with adults mainly expressing carbohydrases and lipases. A nuanced symbiotic relationship exists between gut microbiota and the host, namely, specific resident bacteria supply crucial enzymes for food digestion, while other bacteria are digested and provide assimilable nutrients. Our study further identifies Holothuroidea lineage-specific lysozymes that are restrictedly expressed in the intestines to support bacterial digestion. Overall, this work advances our knowledge of the evolutionary innovations in the sea cucumber digestive system which enable them to efficiently utilize nutrients from seabed sediments and promote food recycling within marine ecosystems.

Genomic and Transcriptional Analysis of the Necroptosis Pathway Elements RIPK and MLKL in Sea Cucumber, Holothuria leucospilota.

Background: Receptor-interacting protein kinases (RIPKs) and mixed-lineage kinase domain-like protein (MLKL) are crucial in regulating innate immune responses and cell death signaling (necroptosis and apoptosis), and are potential candidates for genetic improvement in breeding programs. Knowledge about the RIPK family and MLKL in sea cucumber remains limited. Methods: We searched the genomes of sea cucumber Holothuria leucospilota for genes encoding RIPKs and MLKL, performed phylogenetic tree, motif and functional domain analyses, and examined tissue distribution and embryonic development patterns using qPCR. Results: RIPK5 (Hl-RIPK5), RIPK7 (Hl-RIPK7) and MLKL (Hl-MLKL) were identified in sea cucumber H. leucospilota. Hl-RIPK5 and Hl-RIPK7 were mainly expressed in coelomocytes, suggesting that they play a role in innate immunity, whereas Hl-MLKL exhibited relatively low expression across tissues. During embryonic development, Hl-MLKL was highly expressed from the 2-cell stage to the morula stage, while Hl-RIPK5 and Hl-RIPK7 were primarily expressed after the morula stage, indicating different roles in embryonic development. In primary coelomocytes, Hl-RIPK5 transcriptional activity was significantly depressed by LPS, poly(I:C), or pathogen Vibrio harveyi. Hl-RIPK7 expression levels were unchanged following the same challenges. Hl-MLKL mRNA levels were significantly decreased with poly(I:C) or V. harveyi, but did not change with LPS. Conclusions: These findings provide valuable insights into the evolutionary tree and characterization of RIPK and MLKL genes in sea cucumber, contributing to the broader understanding of the RIPK gene family and MLKL in ancient echinoderms.

Searching for drivers of the patchy distribution of sympatric deposit‐feeding sea cucumbers: A multi‐scale monitoring study

AbstractThree sea cucumber species, Holothuria atra, Holothuria leucospilota, and Stichopus chloronotus, are patchily distributed within the coral reefs of Reunion Island, exhibiting locally high densities (> 1 ind m−2). Previous studies stated that these sympatric species have thrived for almost four decades; however, factors involved in their distribution and spatiotemporal dynamics are not well understood yet. The aims of this study are to analyze the fine‐scale spatiotemporal dynamics of these sympatric species and identify the key sedimentary factors (substrate composition and cover) involved in their distribution. Sea cucumber populations and sedimentary factors were monitored along back‐reef and shore‐to‐ocean gradients during four consecutive seasons. Meanwhile, feeding behavior was assessed by measuring motility and excretion rates. Each species presents its own dynamic between the beginning and the end of the monitoring: increase of density for H. leucospilota, stability for H. atra, and decrease for S. chloronotus. Distribution of H. atra was closely related to substrate organic features (high organic matter, chlorophyll a, and ∂13C), H. leucospilota with the occurrence of seagrass and S. chloronotus with none. Results on feeding behavior showed that S. chloronotus emerges as a specialist while the two others appear to be generalists. Conspecific attraction or recruitment pattern may drive the high‐density patchy distribution of both Holothuria species, while the drastic decrease of S. chloronotus could be linked to unstudied factors related to predation or climate change. Water flow regime could also have a significant effect on the patchy distribution of these species, therefore, further studies should pay particular attention to this factor.

Hepatoprotective effect of Holothuria leucospilota methanolic extract on dimethyl nitrosamine-induced hepatotoxicity in rats.

Complementary medicine is an interesting field for extracting bioactive compounds from various plant and animal sources. The hepatoprotective effect of the methanolic extract of a species of sea cucumber called Holothuria leucospilota in an animal model of liver cancer caused by dimethyl nitrosamine (DMN) was studied. Wistar female rats were randomly divided into five groups (n = 12): control (intact), positive control (received 1% DMN [10 mg/kg/week, intraperitoneally] for 12 weeks), and three treatment groups (received 50, 100, and 200 mg/kg/day H. leucospilota extract orally for 12 weeks along with intraperitoneal administration of 1% DMN [10 mg/kg/week]). In all groups, ultrasound was performed on the liver every week to check its density. Blood sampling and liver isolation were performed on three occasions, at 4, 8, and 12 weeks, to check liver enzymes and the histopathological condition of the liver tissue (every week, four animals from each group were randomly selected). Liver density changes were evident from the eighth week onward in the positive control group. Histopathological results indicated pathologic changes in the positive control group after 4 weeks. The increase in liver enzymes in the positive control group was significantly different from that in the treatment and control groups. We demonstrated the hepatoprotective effect of H. leucospilota on DMN-induced liver damage in rats using biochemical and histological parameters and ultrasonography. More additional research (in silico or invitro) is needed to find the exact mechanism and the main biological compound in H. leucospilota.

Pipeline for identification of genome-wide microsatellite markers and its application in assessing the genetic diversity and structure of the tropical sea cucumber Holothuria leucospilota

Microsatellite DNA (SSR) is extensively used as molecular markers in diverse fields, including molecular ecology, conservation biology, and molecular breeding. Nevertheless, the efficient and easy acquisition of high-quality SSR molecular markers for economically cultured marine animals remains a challenge. Holothuria leucospilota is an economically and ecologically important tropical sea cucumber. Recently, artificial breeding and cultivation of this species have been reported. However, there is still a lack of highly polymorphic SSR molecular markers for geographical population differentiation and genetic breeding. This study aims to develop and utilize SSR markers from genomic data to assess the genetic variation and population structure of H. leucospilota in the South China Sea. A comprehensive pipeline was created, integrating microsatellite discovery, primer design, and assessment into a single platform. Through this, 15 highly polymorphic microsatellite loci were identified and validated. The results revealed high genetic diversity and low genetic differentiation among H. leucospilota populations. Larval dispersal and ocean currents in the South China Sea were identified as the primary factors influencing genetic connectivity between populations. In addition, the artificial culture and releasing of H. leucospilota have influenced the genetic structure of their wild populations in the South China Sea. This study provides a pipeline for identifying SSR markers within genome data, and applies it to assess the genetic diversity and structure of H. leucospilota. The outcomes of this research are expected to be beneficial and applicable to the future aquaculture of tropical sea cucumbers.

Detection of Chromium (Cr) and Lead (Pb) in Marine Sediments and its Bioaccumulation in Holothuria leucospilota (Sea Cucumber) in Jasaan, Misamis Oriental, Philippines

Detection of Chromium (Cr) and Lead (Pb) in Marine Sediments and its Bioaccumulation in Holothuria leucospilota (Sea Cucumber) in Jasaan, Misamis Oriental, Philippines

Holothuria leucospilota polysaccharides (HLP) ameliorate colitis rats via regulation of the metabolic profiling and TLR4/NLRP3 signaling pathways

AbstractRecently, the development of natural polysaccharides for ameliorating immunity and gut metabolism has attracted extensive attention. This study used Holothuria leucospilota polysaccharides (HLP) to explore the improvement mechanism in ulcerative colitis rats on perspectives of immunity and metabolism. The results showed that HLP increased goblet cells’ number and the content of tight junction proteins (zona occludens 1 and occludin) and improved intestinal barrier permeability. The levels of immune cytokines (IL‐4, IL‐6, IL‐10, IL‐18, TNF‐α, and IL‐1β) and the activity of oxidative stress‐related enzymes (superoxide dismutase, catalase, malondialdehyde, and glutathione peroxidase) were regulated. HLP regulated the related genes and proteins expression of immune cytokines, MAPK, and NLRP3 inflammasome. Furthermore, HLP treatment increased the concentration of short‐chain fatty acids (SCFAs) and regulated serum metabolic disorders by regulating amino acid metabolism, SCFA metabolism, and energy metabolism. These results provide a new perspective for developing HLP as a promising functional food for preventing and mitigating colitis.

Relationship of Water Physicochemical Factors with White Thread Fish Holothuria leucospilota (Brandt, 1835) Biomass in the Northern Waters of the Oman Sea

Relationship of Water Physicochemical Factors with White Thread Fish Holothuria leucospilota (Brandt, 1835) Biomass in the Northern Waters of the Oman Sea

Transcriptomic analysis reveals the early body wall regeneration mechanism of the sea cucumber Holothuria leucospilota after artificially induced transverse fission

BackgroundSea cucumbers exhibit a remarkable ability to regenerate damaged or lost tissues and organs, making them an outstanding model system for investigating processes and mechanisms of regeneration. They can also reproduce asexually by transverse fission, whereby the anterior and posterior bodies can regenerate independently. Despite the recent focus on intestinal regeneration, the molecular mechanisms underlying body wall regeneration in sea cucumbers still remain unclear.ResultsIn this study, transverse fission was induced in the tropical sea cucumber, Holothuria leucospilota, through constrainment using rubber bands. Histological examination revealed the degradation and loosening of collagen fibers on day-3, followed by increased density but disorganization of the connective tissue on day-7 of regeneration. An Illumina transcriptome analysis was performed on the H. leucospilota at 0-, 3- and 7-days after artificially induced fission. The differential expression genes were classified and enriched by GO terms and KEGG database, respectively. An upregulation of genes associated with extracellular matrix remodeling was observed, while a downregulation of pluripotency factors Myc, Klf2 and Oct1 was detected, although Sox2 showed an upregulation in expression. In addition, this study also identified progressively declining expression of transcription factors in the Wnt, Hippo, TGF-β, and MAPK signaling pathways. Moreover, changes in genes related to development, stress response, apoptosis, and cytoskeleton formation were observed. The localization of the related genes was further confirmed through in situ hybridization.ConclusionThe early regeneration of H. leucospilota body wall is associated with the degradation and subsequent reconstruction of the extracellular matrix. Pluripotency factors participate in the regenerative process. Multiple transcription factors involved in regulating cell proliferation were found to be gradually downregulated, indicating reduced cell proliferation. Moreover, genes related to development, stress response, apoptosis, and cell cytoskeleton formation were also involved in this process. Overall, this study provides new insights into the mechanisms of whole-body regeneration and uncover potential cross-species regenerative-related genes.

Metabolome and Transcriptome Association Analysis Reveals the Link Between Pigmentation and Nutrition Utilization in the Juveniles of Sea Cucumber Holothuria leucospilota.

The sea cucumber Holothuria leucospilota is an economically and ecologically important tropical species. Following development into juveniles, H. leucospilota undergoes a color change from white to black, involving a pigmentation process for over a period of several months. In this study, a combination of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and Next-Generation sequencing (NGS) were employed to investigate the changes in metabolomic and transcriptomic profiles during pigmentation in H. leucospilota juveniles. The metabolomic analysis identified a total of 341 metabolites, of which 52 were found to be differentially regulated (P < 0.05 and VIP > 1), with 27 being upregulated in white individuals and 25 in black individuals. Additionally, 632 differentially expressed genes (DEGs) were identified, with 380 genes upregulated in white samples and 252 genes upregulated in black samples. Interestingly, the melanin content and tyrosinase transcript levels did not display significant differences between the two groups. Metabolomic data suggested the involvement of the linoleic acid metabolic pathway in pigmentation. Transcriptomic analysis, coupled with realtime PCR validation, revealed a decrease in the transcript levels of digestive enzymes like α-amylase, maltase-glucoamylase, and trehalase after the juveniles changed to black. Furthermore, the mRNA expressions of major yolk proteins showed a decline, indicating a shift in the accumulation of protein nutrient sources. Overall, our findings suggest that during the pigmentation process in H. leucospilota, no significant changes were observed in the classical melanin pathway, while notable alterations were observed in their nutritional status. This study provides valuable insights into the regulatory mechanisms of pigmentation in marine organisms.

UPLC-Q-TOF/MS-based metabonomics reveals mechanisms for Holothuria leucospilota polysaccharides (HLP)-regulated serum metabolic changes in diabetic rats.

This study aimed to use metabolomic methods to explore how Holothuria leucospilota polysaccharides (HLP) improved metabolism disorders in the liver of Goto-Kakizaki (GK) rats with spontaneous type 2 diabetes. The results showed that HLP effectively improved the metabolic disorder. Based on KEGG functional analysis, five key biomarkers associated with bile acid metabolism were detected and screened (P<0.05). The results of serum total bile acid levels and liver damage in diabetic rats further showed the regulatory effects of HLP on bile acid metabolism. The results of bile acid-related gene expression in the liver showed that HLP inhibited liver farnesoidXReceptor - small heterodimer partner (FXR-SHP) signalling and increased the expression of bile acid synthesis genes (P <0.05). Our results explored the underlying mechanisms by which HLP accelerated cholesterol consumption to anti-hypercholesterolemia and anti-diabetic by inhibiting liver FXR-SHP signaling. HLP's effect on bile acid regulation provides insights into treating T2DM.

Timing of the reproductive cycle of Holothuria (Mertensiothuria) leucospilota (Brandt, 1835) from the Persian Gulf based on evaluation of gonad histomorphology and sex hormones

Timing of the reproductive cycle of Holothuria (Mertensiothuria) leucospilota (Brandt, 1835) from the Persian Gulf based on evaluation of gonad histomorphology and sex hormones

Understanding the internal differences behind unsynchronized growth in sea cucumber Holothuria leucospilota by integration of transcriptomic and metabolomic data

In China, there is a rapidly increasing need for the seedlings of tropical sea cucumber, Holothuria leucospilota, as they are often used for releasing to restore fishery resources and marine environments. Unsynchronized growth (NG) of H. leucospilota has been a problem during its culture, and the molecular mechanisms behind NG are rarely explored. In the present study, unsynchronized growing seedlings of H. leucospilota cultured in same environment were random collected after 100 days rearing, and they were classified into a fast-growing (FG) group and a slow-growing (SG) group based on their body weight. Body wall tissues were sheared for metabolomic analysis based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) and transcriptomic analysis with RNA sequencing (RNA-seq). 3243 Differentially expressed genes (DEGs) and 1574 different metabolites (DMs) were identified between two group. Integrated metabolomic and transcriptomic analysis revealed 47 jointly enriched pathways and the FG group had a better capacity for protein and fatty acid synthesis, vitamin synthesis, and oxidative stress regulatory while the SG group experienced more frequent apoptosis. The results facilitate to discover underlying mechanism of NG, which offers prospective benefits for the aquaculture of sea cucumbers.

Transcriptome and metabolome analyses reveal gender-specific expression genes in sea cucumber (Holothuria leucospilota)

The sea cucumber Holothuria leucospilota, a nutritive and commercial marine species, has a high protein and low lipid content. To date, the mechanisms underlying gender determination and differentiation in sea cucumbers remain unclear. Identifying gender-specific molecular markers is an effective method of revealing the genetic basis of gender determination and differentiation. The inability to distinguish between male and female individuals causes reproductive efficiency to decline in aquaculture. In this study, we used the gonads of the sea cucumber H. leucospilota as samples to conduct the experiment. The differentially abundant metabolites (DAMs) detected by liquid chromatography-mass spectrometry were enriched in pathways associated with prolactin metabolism, insulin metabolism, hypoxia-inducible factor-1 signaling, and calcium signaling. At the transcriptome level, Illumina sequencing was performed on H. leucospilota, demonstrating that gender-specific expression genes were enriched in the retinoic acid-inducible gene I-like receptor signaling pathway, C-type lectin receptor signaling pathway, alpha-linolenic acid metabolism, and ether lipid metabolism by the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. By analyzing the common pathways between DAMs and differentially expressed genes, we found that gender-related genes of H. leucospilota were mostly enriched in the necroptosis pathway and the cysteine and methionine metabolism pathways. According to the common pathways, uch-sc1 and uch-sc2 are male-specific expression genes, and uch-sc3 and bhmt are female-specific expression genes at the mRNA level. These results provide information on gender differences in H. leucospilota.

Antibacterial and antioxidant activity of sea cucumber extracts collected from Lampung waters, Indonesia

Sea cucumbers are the most prevalent marine invertebrates in Indonesian waters, yet little research has been conducted on the bioactive substances found in the sea cucumbers harvested from these waters. To investigate the potential use of sea cucumber extracts and fractions such as antibacterial and antioxidant agents, five sea cucumber species were harvested from Lampung waters in Indonesia. The extraction process used the maceration method with methanol solvent, while fractionation was carried out with n-hexane, ethyl acetate, and butanol solvents. The antibacterial activity was evaluated using the agar diffusion method, and the antioxidant activity was assessed using the ABTS (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) method. The GC–MS method was used to identify the compounds in the methanol extract and butanol fraction of Holothuria lessoni. The results showed that only the n-hexane fraction of Stichopus quadrifasciatus and the methanol extract of H. lessoni had antibacterial activity against Propionibacterium acnes, while the methanol extract of H. lessoni and the ethyl acetate fraction of H. leucospilota showed activity against Staphylococcus aureus. The n-hexane fraction of S. quadrifasciatus and the methanol extract of H. lessoni and Bohadschia marmorata recorded activity against Staphylococcus epidermidis. Among the tested extracts, Holothuria leucospilota showed the highest antioxidant activity in methanol extracts, with an IC50 value of 155.07 ​± ​3.05 ​μg/mL, followed by H. lessoni (163.83 ​± ​4.46 ​μg/mL), Stichopus vastus (209.45 ​± ​2.40 ​μg/mL), S. quadrifasciatus (245.85 ​± ​34.97 ​μg/mL), and B. marmorata (382.86 ​± ​45.37 ​μg/mL), respectively. Cyclononasiloxane, octadecamethyl- (C18H54O9Si9), cyclohexasiloxane, dodecamethyl (C12H36O6Si), and cyclooctasiloxane, hexadecamethyl- (C16H48O8Si8) were identified as the main compounds in the tested samples using GC–MS analysis. In conclusion, H. lessoni is a valuable source of natural antibacterial and antioxidant agents.

Genome-wide analysis of the intrinsic apoptotic pathway in the tropical sea cucumber Holothuria leucospilota

To date, studies on apoptosis in echinoderms mainly focus on the caspase-dependent extrinsic apoptotic pathway, while knowledges regarding the intrinsic apoptotic pathway is still limited. In this study, 55 genes belong to 7 families of the intrinsic apoptotic pathway, namely, Bcl-2, caspase, AIF, Cyt c, Apaf-1, Smac, HTRA2 and Endo G, were identified by screening of the genomic database of the tropical sea cucumber Holothuria leucospilota. The Bcl-2 family showed significant gene expansion in H. leucospilota but not in other echinoderms, while the pro-apoptotic factor Endo G is generally lost in echinoderms. Transcriptomic data showed that the genes of the intrinsic apoptotic pathway were ubiquitously expressed in all tissues, and all embryonic and larval developmental stages of H. leucospilota. The gene numbers and functional domains of the caspase family and AIF family were further clarified and showed conserved with their counterparts in vertebrates. In primary coelomocytes, the transcript expression of different caspases showed different responses to pathogenic challenges of vibrio and pathogen-associated molecular patterns, and environmental challenges of heave metal and reactive oxygen species. Overall, this study indicates that the intrinsic apoptotic pathway is conserved between vertebrates and echinoderms by using the sea cucumber H. leucospilota as a model. This study may contribute in increasing the knowledge of development and innate immunity in ancestral deuterostomia species.

Bioecology study of Holothuroidea (sea cucumbers) in the northern coastal area of Timor Island, East Nusa Tenggara

Holothuroidea is one of the marine biotas with crucial economic value in Asia and is usually served fresh or dried in various cuisines. Although it has significant market demand, the potential of sea cucumbers in the northern part of Timor Island has yet to be investigated. This study was carried out to understand existing bioecological conditions and investigate the location’s suitability to support the development of sea cucumber farming in this area. The method employed in the bioecology study followed a line transect and quadrants perpendicular to the beach. Various water quality measurements were applied to quantify the location suitability index. The results observed four species in the Poanboun coastal area: Holothuria leucospilota, H. hilla, Bohadschia argus, and H. atra (the order indicates the highest to lowest density and abundance). The substrate types in the area were a combination of sandy, muddy sand, coral fragments, and surrounded sea grapes macroalgae. The region has a high location suitability index where secluded area, water depth and bed, temperature, salinity, pH, DO, and wave conditions are prime indicators to support the suitability, followed by water clarity and current as secondary (quite supportive indicators).

Artificial spawning, hatchery and culture of the tropical sea cucumber (Holothuria leucospilota) using non-living food

Artificial breeding and farming of sea cucumber is considered as a sustainable way to meet market demand and minimize the pressure on wild populations. This study reports a method for large-scale artificial spawning, hatchery and culture of the tropical sea cucumber (Holothuria leucospilota). Spawning induction was performed by constant stimulation and dry shock. Both methods could obtain active and healthy fertilized eggs, but constant stimulation could get a greater oviposition amount of H. leucospilota. Among the six tested non-living food, the Spirulina platensis meal contains the highest contents of crude protein and total amino acids, and the Chlorella pyrenoidosa powder contains most abundant types of fatty acid. However, only the C. pyrenoidosa powder fed larvae could successfully develop to doliolaria stage. H. leucospilota fed C. pyrenoidosa powder had similar (P > 0.05) growth rate and survival rate but higher (P < 0.05) metamorphosis rate than that fed living Chaetoceros muelleri. The contents of crude protein and total amino acids of Saccharomyces cerevisiae yeast meal between that of C. muelleri and C. pyrenoidosa powder, but it failed to induce larval metamorphosis. The best diet scheme was mixing C. pyrenoidosa powder, S. cerevisiae yeast powder and sea mud followed by the ratio of 2:1:2 with the installment feeding mode, which reached the highest development rate of H. leucospilota. In summary, a simple and successful technology for large-scale artificial reproduction of H. leucospilota is set up in this study, which not only provide an excellent candidate for aquaculture in tropical regions, but also conducive to recover and reconstruct the wild population of sea cucumber.

Sex or Fission? Genetics Highlight Differences in Reproductive Strategies of Two Sympatric Fissiparous Sea Cucumber Species in Reunion Island (Southwestern Indian Ocean)

Holothuria leucospilota and Stichopus chloronotus are among the most widespread tropical sea cucumber species usually harvested for food and medicine in Asian countries, for which natural stocks have collapsed worldwide. Both species can reproduce sexually and asexually, and a better understanding of their reproductive strategy can provide useful information for conservation purposes. To describe the genetic structure and diversity of sympatric populations from these species in space and time, individuals were sampled over different sites and seasons in Reunion Island (Southwestern Indian Ocean). They were genotyped using 24 and 9 specific microsatellite markers for H. leucospilota and S. chloronotus, respectively. Multi-locus genotypes (MLG) and lineages (MLL) were identified, and analyses of population structure were performed among sites and seasons. No repeated MLG nor MLL were found for H. leucospilota, demonstrating the absence of asexual reproduction. Populations of H. leucospilota were not genetically differentiated, acting as a metapopulation, with larval exchanges within the reef. Contrarily, repeated MLGs were found for S. chloronotus and all populations were genetically differentiated. Asexual reproduction seems to reach a high level for this species (mean clonal richness = 0.24). For both species, genetic structure was stable through seasons. Thus, these sympatric fissiparous sea cucumber species use two different strategies of reproduction, which may allow them to reduce interspecific competition.