Experimental evidence of a sex reversal process in the shrimpHippolyte inermis

Cell-Death Metabolites from Cocconeis scutellum var. parva Identified by Integrating Bioactivity-Based Fractionation and Non-Targeted Metabolomic Approaches

Epiphytic diatoms growing in Mediterranean seagrass meadows, particularly those of the genus Cocconeis, are abundant and ecologically significant, even in naturally acidified environments. One intriguing aspect of some benthic diatoms is their production of an unidentified cell-death-promoting compound, which induces destruction of the androgenic gland in Hippolyte inermis Leach, 1816, a shrimp exhibiting protandric hermaphroditism, principally under normal environmental pH levels. The consumption of Cocconeis spp. by this shrimp is vital for maintaining the stability of its natural populations. Although many attempts have been made to reveal the identity of the apoptotic compound, it is still unknown. In this study, we strategically integrated a bioactivity-based fractionation, a metabolomic approach, and two different experimental avenues to identify potential apoptotic metabolites from Cocconeis scutellum var. parva responsible for the sex reversal in H. inermis. Our integrated analysis uncovered two potential candidate metabolites, one putatively identified as a lysophosphatidylglycerol (LPG) (16:1) and the other classified as a fatty acid ester. This is the first time LPG (16:1) has been reported in C. scutellum var. parva and associated with cell-death processes. These candidate metabolites mark substantial progress in elucidating the factors responsible for triggering the removal of the androgenic gland in the early post-larval phases of H. inermis.

Ferroptosis precedes apoptosis to facilitate specific death signalling by fatty acids

Cell death is physiologically induced by specific mediators. However, our power to trigger the process in selected cells is quite limited. The protandric shrimp Hippolyte inermis offers a possible answer. Here, we analyse a de novo transcriptome of shrimp post-larvae fed on diatoms. The sex ratio of diatom-fed shrimps versus shrimps fed on control diets was dramatically altered, demonstrating the disruption of the androgenic gland, and their transcriptome revealed key modifications in gene expression. A wide transcriptomic analysis, validated by real-time qPCR, revealed that ferroptosis represents the primary factor to re-shape the body of this invertebrate, followed by further apoptotic events, and our findings open biotechnological perspectives for controlling the destiny of selected tissues. Ferroptosis was detected here for the first time in a crustacean. In addition, this is the first demonstration of a noticeable effect prompted by an ingested food, deeply impacting the gene networks of a young metazoan, definitely determining its future physiology and sexual differentiation.

Reproductive Variability in Hippolytid Shrimp Shape Morphotypes

Shape morph-specific studies in hippolytid shrimps revealed significant results on their ecomorphology and evolutionary adaptations. Among the species of the genus Hippolyte, only one exhibits an unusual, sharp rostral dimorphism and has been used as an animal model for the investigation of mechanisms of the morph-specific adaptation: the intertidal Hippolyte sapphica. The species is endemic of the Central/Eastern Mediterranean basin and exhibits morph-A with a long dentate rostrum and morph-B with a short, juvenile-like one. The two morphotypes were recently confirmed to be conspecific, while offspring and morphological studies showed significant microevolutionary adaptations, which balance the disadvantage of the “rostral loss.” The present study aims to investigate the effect of such phenotypic variation on the reproductive traits of the species. We collected ovigerous females of H. sapphica in mixed (morph-A and morph-B) and unmixed populations (morph-A) along the species geographical range. We measured seven morphometric and maternal investment traits: carapace length, fecundity, embryo volume, egg density, female dry weight, brood dry weight, and reproductive output. Our results showed that ovigerous females were bigger in morph-A than in morph-B, whereas fecundity did not show any significant differences between the two morphotypes. High egg volume might be attributed to the latitudinal differences of our sampling sites compared to congenerics. Interestingly, the reproductive output was found to be bigger in morph-A specimens, suggesting that the maternal energy investment is selectively determined from the rostral presence/absence and the morphotype’s higher viability in the species populations.

Ocean acidification influences plant-animal interactions: The effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis

Ocean acidification (O.A.) influences the ecology of oceans and it may impact plant-animal interactions at various levels. Seagrass meadows located at acidified vents in the Bay of Naples (Italy) are considered an open window to forecast the effects of global-changes on aquatic communities. Epiphytic diatoms of the genus Cocconeis are abundant in seagrass meadows, including acidified environments, where they play key ecological roles. A still-unknown apoptogenic compound produced by Cocconeis triggers the suicide of the androgenic gland of Hippolyte inermis Leach 1816, a protandric hermaphroditic shrimp distributed in P. oceanica meadows located both at normal pH and in acidified vents. Feeding on Cocconeis sp. was proven important for the stability of the shrimp's natural populations. Since O.A. affects the physiology of diatoms, we investigated if, in future scenarios of O.A., Cocconeis scutellum parva will still produce an effect on shrimp's physiology. Cell densities of Cocconeis scutellum parva cultivated in custom-designed photobioreactors at two pH conditions (pH 7.7 and 8.2) were compared. In addition, we determined the effects of the ingestion of diatoms on the process of sex reversal of H. inermis and we calculated the % female on the total of mature individuals-1 (F/mat). We observed significant differences in cell densities of C. scutellum parva at the two pH conditions. In fact, the highest cell densities (148,808 ±13,935 cells. mm-2) was obtained at day 13 (pH 7.7) and it is higher than the highest cell densities (38,066 (±4,166) cells. mm-2, day 13) produced at pH 8.2. Diatoms cultured at acidified conditions changed their metabolism. In fact, diatoms grown in acidified conditions produced in H. inermis a proportion of females (F/mat 36.3 ±5.9%) significantly lower than diatoms produced at normal pH (68.5 ±2.8), and it was not significantly different from that elicited by negative controls (31.7 ±5.6%).

Noxious effects of the benthic diatoms Cocconeis scutellum and Diploneis sp. on sea urchin development: Morphological and de novo transcriptomic analysis

Diatoms are often the dominating group of benthic microalgae living on different types of bottom substrates. Their effects on invertebrate consumers is not well-documented. We here investigate the effects of feeding on another two benthic diatoms, Cocconeis scutellum and Diploneis sp., isolated from leaves of the seagrass Posidonia oceanica, on the sea urchin Paracentrotus lividus. Our results indicate a noxious effect on sea urchin embryos spawned from adults fed on Diploneis sp., with an increasing number of malformed embryos with respect to those spawned from adults fed on Ulva rigida (used as a feeding control). In contrast C. scutellum did not induce any morphological effect on embryos, similar to control non-diatom diets. Moreover, de novo obtained transcriptome indicated that oxidation-reduction process, translation, proton and electron transmembrane transport, ATP/RNA/GTP/heme/calcium and metal ion binding, NADH dehydrogenase activity, cytochrome c oxidase were affected by feeding of sea urchins on Diploneis sp. Our findings have considerable ecological significance considering that diatom biomass ingested by the sea urchin in these experiments is within the range of cell densities characterizing P. oceanica leaves where sea urchins live and spawn.

The sex change of the caridean shrimp Hippolyte inermis Leach: temporal development of the gonopore morphology

Sex reversal is a process observed in several marine organisms, including some lineages of caridean shrimps. We investigated the gonopore shape and size, to study the sex reversal using Hippolyte inermis as a model. A method was developed which can be applied to identify the sex in juveniles of H. inermis, especially, useful when the standard method of sex assessment is not applicable. The position and the shape of gonopores was recorded under a light macroscope. The sex of mature individuals was then determined by observing the presence/absence of the appendix masculina. In addition, analysis of ontogenetic changes of gonopores were performed to compare their morphology with other species of shrimps whose gonopore morphology was previously known. Female gonopores are located at the far proximo-medial end of the third pair of pereiopod coxae and distally they bear cup-shaped structures, whilst male gonopores are located at the far proximo-medial end of the fifth pair of pereiopod coxae and they have a simpler structure. The shape and structure of gonopores in H. inermis resembled that of other caridean decapods. Intersex individuals were never observed, although this species was demonstrated to be protandric. This observation confirmed previous assumptions indicating that the process of sex reversal is very fast in H. inermis and that it takes place within a single moult. The identification of sex based on the position and shape of gonopores is feasible in this species, and it provides helpful insights for studying sex reversal in small decapods.

Toxigenic effects of two benthic diatoms upon grazing activity of the sea urchin: morphological, metabolomic and de novo transcriptomic analysis

Diatoms are unicellular algae playing a key role as photosynthetic organisms in the world's ocean food webs. The chemical ecology of planktonic diatoms is well documented, but few studies have reported on the effects of benthic diatoms on their consumers, also due to difficulties in the collection, quantification and massive culturing of benthic species. Here for the first time we investigate the effects of feeding on two abundantly occurring benthic diatoms, Nanofrustulum shiloi and Cylindrotheca closterium, isolated from the leaves of the seagrass Posidonia oceanica, on the sea urchin Paracentrotus lividus. Adult P. lividus were fed for one month on diets of either one of the two diatoms and on the green alga Ulva rigida, used as a feeding control. By combining morphological, metabolomic and de novo transcriptomic approaches, we demonstrate toxigenic effect on embryos generated by females fed with these benthic diatoms. Furthermore, chemical analysis reveal the presence of polyunsaturated aldehydes only for N. shiloi, and a high production of other oxylipins (cytotoxic compounds on their grazers and on cancer cell lines) for both diatoms, including some additional peaks not correlated to the canonic oxylipins commonly observed in planktonic diatoms. These findings open new perspectives in the study of diatom secondary metabolites influencing their grazers.

Automated culture of aquatic model organisms: shrimp larvae husbandry for the needs of research and aquaculture

Modern research makes frequent use of animal models, that is, organisms raised and bred experimentally in order to help the understanding of biological and chemical processes affecting organisms or whole environments. The development of flexible, reprogrammable and modular systems that may help the automatic production of 'not-easy-to-keep' species is important for scientific purposes and for such aquaculture needs as the production of alive foods, the culture of small larvae and the test of new culture procedures. For this reason, we planned and built a programmable experimental system adaptable to the culture of various aquatic organisms, at different developmental stages. The system is based on culture cylinders contained into operational tanks connected to water conditioning tanks. A programmable central processor unit controls the operations, that is, water changes, temperature, light irradiance, the opening and closure of valves for the discharge of unused foods, water circulation and filtration and disinfection systems, according to the information received by various probes. Various devices may be set to modify water circulation and water changes to fulfil the needs of given organisms, to avoid damage of delicate structures, improve feeding performances and reduce the risk of movements over the water surface. The results obtained indicate that the system is effective in the production of shrimp larvae, being able to produce Hippolyte inermis post-larvae with low mortality as compared with the standard operation procedures followed by human operators. Therefore, the patented prototype described in the present study is a possible solution to automate and simplify the rearing of small invertebrates in the laboratory and in production plants.

Trophic Ecology of Benthic Marine Invertebrates with Bi-Phasic Life Cycles: What Are We Still Missing?

The study of trophic ecology of benthic marine invertebrates with bi-phasic life cycles is critical to understand the mechanisms shaping population dynamics. Moreover, global climate change is impacting the marine environment at an unprecedented level, which promotes trophic mismatches that affect the phenology of these species and, ultimately, act as drivers of ecological and evolutionary change. Assessing the trophic ecology of marine invertebrates is critical to understanding maternal investment, larval survival to metamorphosis, post-metamorphic performance, resource partitioning and trophic cascades. Tools already available to assess the trophic ecology of marine invertebrates, including visual observation, gut content analysis, food concentration, trophic markers, stable isotopes and molecular genetics, are reviewed and their main advantages and disadvantages for qualitative and quantitative approaches are discussed. The challenges to perform the partitioning of ingestion, digestion and assimilation are discussed together with different approaches to address each of these processes for short- and long-term fingerprinting. Future directions for research on the trophic ecology of benthic marine invertebrates with bi-phasic life cycles are discussed with emphasis on five guidelines that will allow for systematic study and comparative meta-analysis to address important unresolved questions.

Apoptogenic metabolites in fractions of the Benthic diatom Cocconeis scutellum parva

Benthic diatoms of the genus Cocconeis contain a specific apoptogenic activity. It triggers a fast destruction of the androgenic gland in the early post-larval life of the marine shrimp Hippolyte inermis, leading to the generation of small females. Previous in vitro investigations demonstrated that crude extracts of these diatoms specifically activate a dose-dependent apoptotic process in human cancer cells (BT20 breast carcinoma) but not in human normal lymphocytes. Here, a bioassay-guided fractionation has been performed to detect the apoptogenic compound(s). Various HPLC separation systems were needed to isolate the active fractions, since the apoptogenic metabolite is highly active, present in low amounts and is masked by abundant but non-active cellular compounds. The activity is due to at least two compounds characterized by different polarities, a hydrophilic and a lipophilic fraction. We purified the lipophilic fraction, which led to the characterization of an active sub-fraction containing a highly lipophilic compound, whose molecular structure has not yet been identified, but is under investigation. The results point to the possible medical uses of the active compound. Once the molecular structure has been identified, the study and modulation of apoptotic processes in various types of cells will be possible.