Contributions of larval biology to crustacean research: a review

Identification and Physiological Assays of Crustacean Hyperglycemic Hormones in the Japanese Spiny Lobster, Panulirus japonicus

The Japanese spiny lobster Panulirus japonicus lives on rocky shores and is mainly distributed along the Pacific coast around Japan. Due to the high demand for it, the development of aquaculture systems and increasing its resource volume requires further expansive production. However, a major factor preventing the establishment of aquaculture technology for this lobster is the difficulty with rearing processes from larval to juvenile production. A recent study shed light on the molecular mechanisms underlying larval development from the perspective of physiological functions of endocrine factors such as molting hormones. However, physiological studies of P. japonicus are still lacking. In decapod crustaceans, the X-organ/sinus gland complex is a well-known endocrine system that secretes the crustacean hyperglycemic hormone (CHH)-superfamily peptides that regulate growth, molting, sexual maturation, reproduction, and change in body color. In this study, we identified two CHHs from the sinus glands of P. japonicus using reversed-phase high-performance liquid chromatography in order to elucidate their physiological function for the first time.

Boom and bust: Simulating the effects of climate change on the population dynamics of a global invader near the edge of its native range

Despite the increasing awareness of climate change, few studies have used the Intergovernmental Panel on Climate Change (IPCC) scenarios to simulate the effects of climate change on estuarine populations of crustaceans. The objective of this study was to investigate the effects of temperature and salinity fluctuations on the population dynamics of the shore crab Carcinus maenas at the southern edge of its native range. To this end, a population dynamics model was developed based on experimental and literature data on the biology, ecology and physiology of the species. Results showed that the shore crab will be more affected by changes in temperature than in salinity. The parameter sensitivity analysis revealed that the larval phase of the species is the most sensitive stage of the shore crab life cycle. Three IPCC scenarios (SSP1-2.6, SSP2-4.5, and SSP3-8.5) were used to simulate the effects of temperature increase on the population of C. maenas in the near- (2040), mid- (2060), and long-term (2100). Two scenarios of drought conditions accompanied by the estimated salinity change were also simulated (10 % and 40 % drought). Results suggested that slight increases in temperature (up to 2 °C) lead to a strong increase on the density of C. maenas in the mid-term, while further temperature increases lead to a decline or local extinction of the shore crab population at the southern edge of its distribution range. Results indicated that a salinity increase in the estuary had a negative effect on the shore crab population. Given the importance of the species to temperate coastal ecosystems, both population increase and local extinction are likely to have significant impacts on estuarine communities and food webs, with unknown ecological and socioeconomic consequences.

Ontogenetical development of branchial chambers of Litopenaeus vannamei (Boone, 1931) and their involvement in osmoregulation: ionocytes and Na+/K+-ATPase

Branchial chambers constitute the main osmoregulatory site in almost all decapod crustaceans. However, few studies have been devoted to elucidate the cellular function of specific cells in every osmoregulatory structure of the branchial chambers. In decapod crustaceans, it is well-known that the osmoregulatory function is localized in specific structures that progressively specialize from early developmental stages while specific molecular mechanisms occur. In this study, we found that although the structures developed progressively during the larval and postlarval stages, before reaching juvenile or adult morphology, the osmoregulatory capabilities of Litopenaeus vannamei were gradually established only during the development of branchiostegites and epipodites, but not gills. The cellular structures of the branchial chambers observed during the larval phase do not present the typical ultrastructure of ionocytes, neither Na⁺/K⁺-ATPase expression, likely indicating that pleura, branchiostegites, or bud gills do not participate in osmoregulation. During early postlarval stages, the lack of Na⁺/K⁺-ATPase immunoreactivity of the ionocytes from the branchiostegites and epipodites suggests that they are immature ionocytes (ionocytes type I). It could be inferred from IIF and TEM results that epipodites and branchiostegites are involved in iono-osmoregulation from PL15, while gills and pleura do not participate in this function.

Ecology and Distribution of Red King Crab Larvae in the Barents Sea: A Review

The red king crab (RKC) is a large invasive species inhabiting bottom communities in the Barents Sea. Larval stages of RKC play an important role in determining the spread and recruitment of the population in the coastal waters. We present a review of studies concerned with the ecology of RKC larvae in the Barents Sea focusing on their dynamics and role in the trophic food webs as well as on the role of environmental factors in driving RKC zoeae. Zoeal stages are larger, and their development time is shorter in the Barents Sea compared to the North Pacific. RKC larvae appear in late January–February and can be found in the coastal plankton until mid-July. Mass hatching of RKC larvae in the Barents Sea starts in late March-early April. The highest densities of RKC larvae are located in small semi-enclosed bays and inlets with weak water exchange or local eddies as well as in inner parts of fjords. Size structures of the zoeal populations are similar in the inshore waters to the west of Kola Bay but slightly differ from those in more eastern regions. RKC larvae perform daily vertical migrations and move to deeper depths during bright daylight hours and tend to rise during night hours. RKC larvae are plankton feeders that ingest both phyto- and zooplankton. A set of environmental variables including food conditions, water temperature, and advective influence are the most important factors driving the spatial distribution, phenology, survival rates, development, growth, and interannual fluctuations of RKC larvae. Recent climatic changes in the Arctic may have both negative and positive consequences for RKC larvae.

Factors Modulating the Female Reproductive Performance of the Fiddler Crab Leptuca uruguayensis with Short Reproductive Season

AbstractThis study aimed to evaluate the factors modulating the female reproductive performance of the fiddler crab Leptuca uruguayensis (Nobili, 1901) during the short reproductive season of a temperate population. We proposed two modulating factors: the age of females (young and old) and the periods of the reproductive season (beginning, middle, and end); we then evaluated the fecundity, reproductive output, egg volume, and biochemical composition of eggs. The fecundity of L. uruguayensis was affected by the size of females, a variable related to their age. Although young females showed lower fecundity, the reproductive output was not affected by the age or by the periods of the reproductive season, suggesting a constant reproductive effort, proportional to female size. The egg volume decreased, and carotenoid content increased at the end of the season for both female ages, probably as a consequence of variations in food availability and changes in the breeding strategies during the season. However, the content of protein and lipids in the egg clutches decreased at the end of the season only in old females spawning for the second time in the season. The main differences in the reproductive parameters were recorded between the beginning and the end of the reproductive season, probably because in these periods females exclusively use one of the breeding strategies. Finally, we determined that both factors, that is, female age and the periods of the short reproductive season, can modulate the reproductive performance of L. uruguayensis in temperate estuaries.

DNA barcoding allows identification of undescribed crab megalopas from the open sea

Megalopas of 15 brachyuran crab species collected in the open sea plankton, and unknown until now, were identified using DNA barcodes (COI and 16S rRNA). Specimens belonging to the families Portunidae, Pseudorhombilidae and Xanthidae (Crustacea, Decapoda, Brachyura), and corresponding to the species Achelous floridanus, Arenaeus mexicanus, Callinectes amnicola, C. arcuatus, C. ornatus, C. toxones, Charybdis (Charybdis) hellerii, Portunus hastatus, Thalamita admete, Scopolius nuttingi, Etisus odhneri, Liomera cinctimanus, Neoliomera cerasinus, Pseudoliomera variolosa, and Williamstimpsonia stimpsoni, are described and illustrated, and compared with other congeneric species previously described. We also provide a new geographical record for N. cerasinus and the most remarkable features for each species.

Correlated evolution of larval development, egg size and genome size across two genera of snapping shrimp

Across plants and animals, genome size is often correlated with life-history traits: large genomes are correlated with larger seeds, slower development, larger body size and slower cell division. Among decapod crustaceans, caridean shrimps are among the most variable both in terms of genome size variation and life-history characteristics such as larval development mode and egg size, but the extent to which these traits are associated in a phylogenetic context is largely unknown. In this study, we examine correlations among egg size, larval development and genome size in two different genera of snapping shrimp, Alpheus and Synalpheus, using phylogenetically informed analyses. In both Alpheus and Synalpheus, egg size is strongly linked to larval development mode: species with abbreviated development had significantly larger eggs than species with extended larval development. We produced the first comprehensive dataset of genome size in Alpheus (n = 37 species) and demonstrated that genome size was strongly and positively correlated with egg size in both Alpheus and Synalpheus. Correlated trait evolution analyses showed that in Alpheus, changes in genome size were clearly dependent on egg size. In Synalpheus, evolutionary path analyses suggest that changes in development mode (from extended to abbreviated) drove increases in egg volume; larger eggs, in turn, resulted in larger genomes. These data suggest that variation in reproductive traits may underpin the high degree of variation in genome size seen in a wide variety of caridean shrimp groups more generally.

Physiological basis of interactive responses to temperature and salinity in coastal marine invertebrate: Implications for responses to warming

Developing physiological mechanistic models to predict species' responses to climate-driven environmental variables remains a key endeavor in ecology. Such approaches are challenging, because they require linking physiological processes with fitness and contraction or expansion in species' distributions. We explore those links for coastal marine species, occurring in regions of freshwater influence (ROFIs) and exposed to changes in temperature and salinity. First, we evaluated the effect of temperature on hemolymph osmolality and on the expression of genes relevant for osmoregulation in larvae of the shore crab Carcinus maenas. We then discuss and develop a hypothetical model linking osmoregulation, fitness, and species expansion/contraction toward or away from ROFIs. In C. maenas, high temperature led to a threefold increase in the capacity to osmoregulate in the first and last larval stages (i.e., those more likely to experience low salinities). This result matched the known pattern of survival for larval stages where the negative effect of low salinity on survival is mitigated at high temperatures (abbreviated as TMLS). Because gene expression levels did not change at low salinity nor at high temperatures, we hypothesize that the increase in osmoregulatory capacity (OC) at high temperature should involve post-translational processes. Further analysis of data suggested that TMLS occurs in C. maenas larvae due to the combination of increased osmoregulation (a physiological mechanism) and a reduced developmental period (a phenological mechanisms) when exposed to high temperatures. Based on information from the literature, we propose a model for C. maenas and other coastal species showing the contribution of osmoregulation and phenological mechanisms toward changes in range distribution under coastal warming. In species where the OC increases with temperature (e.g., C. maenas larvae), osmoregulation should contribute toward expansion if temperature increases; by contrast in those species where osmoregulation is weaker at high temperature, the contribution should be toward range contraction.

Fine-scale conditions across mangrove microhabitats and larval ontogeny contributes to the thermal physiology of early stage brachyurans (Crustacea: Decapoda)

Most marine ectotherms require the successful completion of a biphasic larval stage to recruit into adult populations. Recruitment of larvae into benthic habitats largely depends on biological interactions and favourable environmental conditions such as the inescapable diurnal thermal and tidal exposures. Hence, assessing how different taxa metabolically respond to variations in temperature is imperative to understand the community and ecosystem dynamics at both local and global scales. The present study aimed to investigate the effects of acute temperature variation on the physiology of stage-specific brachyuran larvae collected from different microhabitats at two mangrove forests in South Africa. Results indicate that the conditions within microhabitats, which larvae experience, likely influence their physiology, based on respirometry, to short-term acute temperature exposures. Furthermore, the larval thermal optimum shifted ontogenetically to become increasingly eurythermic as individuals developed from stage I zoea through to megalopa. Mangrove crab larvae in their early stages are hence increasingly vulnerable to acute temperature exposures, which could be particularly harmful to the persistence of populations if thermally stressful events increase in magnitude and frequency.

The Neurobiology of Ocean Change - insights from decapod crustaceans

The unprecedented rate of carbon dioxide accumulation in the atmosphere has led to increased warming, acidification and oxygen depletion in the world's oceans, with projected impacts also on ocean salinity. In this perspective article, we highlight potential impacts of these factors on neuronal responses in decapod crustaceans. Decapod crustaceans comprise more than 8,800 marine species which have colonized a wide range of habitats that are particularly affected by global ocean change, including estuarine, intertidal, and coastal areas. Many decapod species have large economic value and high ecological importance because of their global invasive potential and impact on local ecosystems. Global warming has already led to considerable changes in decapod species' behavior and habitat range. Relatively little is known about how the decapod nervous system, which is the ultimate driver of all behaviors, copes with environmental stressors. We use select examples to summarize current findings and evaluate the impact of current and expected environmental changes. While data indicate a surprising robustness against stressors like temperature and pH, we find that only a handful of species have been studied and long-term effects on neuronal activity remain mostly unknown. A further conclusion is that the combined effects of multiple stressors are understudied. We call for greater research efforts towards long-term effects on neuronal physiology and expansion of cross-species comparisons to address these issues.

Global Analysis of Gene Expression Profiles Provides Novel Insights into the Development and Evolution of the Large Crustacean Eriocheir sinensis

Chinese mitten crab (Eriocheir sinensis) is an important aquaculture species in Crustacea. Functional analysis, although essential, has been hindered due to the lack of sufficient genomic or transcriptomic resources. In this study, transcriptome sequencing was conducted on 59 samples representing diverse developmental stages (fertilized eggs, zoea, megalopa, three sub-stages of larvae, juvenile crabs, and adult crabs) and different tissues (eyestalk, hepatopancreas, and muscle from juvenile crabs, and eyestalk, hepatopancreas, muscle, heart, stomach, gill, thoracic ganglia, intestine, ovary, and testis from adult crabs) of E. sinensis. A comprehensive reference transcriptome was assembled, including 19,023 protein-coding genes. Hierarchical clustering based on 128 differentially expressed cuticle-related genes revealed two distinct expression patterns during the early larval developmental stages, demonstrating the distinct roles of these genes in “crab-like” cuticle formation during metamorphosis and cuticle calcification after molting. Phylogenetic analysis of 1406 one-to-one orthologous gene families identified from seven arthropod species and Caenorhabditis elegans strongly supported the hypothesis that Malacostraca and Branchiopoda do not form a monophyletic group. Furthermore, Branchiopoda is more phylogenetically closely related to Hexapoda, and the clade of Hexapoda and Branchiopoda and the clade of Malacostraca belong to the Pancrustacea. This study offers a high-quality transcriptome resource for E. sinensis and demonstrates the evolutionary relationships of major arthropod groups. The differentially expressed genes identified in this study facilitate further investigation of the cuticle-related gene expression networks which are likely associated with “crab-like” cuticle formation during metamorphosis and cuticle calcification after molting.

Genetic analyses reveal temporal stability and connectivity pattern in blue and red shrimp Aristeus antennatus populations

Temporal variability of the genetic structure and connectivity patterns of the blue and red shrimp Aristeus antennatus in the seven most important fishing grounds of the Western Mediterranean Sea, were assessed using twelve microsatellite loci during 2 consecutive years (2016 and 2017), in a total of 1403 adult individuals. A high level of geographical connectivity among groups was observed in the two studied years. In fact, no significant geographical differentiation was found in 2016 (F_ST = 0.0018, p > 0.05), whereas it was indicated in 2017 (F_ST = 0.0025, p < 0.05). This small divergence in 2017 was not attributed to the distance among locations nor to the effect of the Ibiza Channel. Significant allele frequency changes were found at local level between the 2 years (F_CT = 0.0006, p < 0.05), mainly due to Blanes’ fishing ground. Larval dispersal from the North to the South through the main superficial current supports the high level of connectivity pattern found. The temporal genetic instability detected in the Blanes’ fishing ground could be explained by oceanographic temporary features. Our findings evidence only one biological unit in the study region and establish the baseline for an inter-federal management plan of A. antennatus.

Visual metamorphoses in insects and malacostracans: Transitions between an aquatic and terrestrial life

Arthropods operate in an outrageous diversity of environments. From the deep sea to dense tropical forests, to wide open arctic tundra, they have colonized almost every possible habitat. Within these environments, the presence of light is nearly ubiquitous, varying in intensity, wavelength, and polarization. Light provides critical information about the environment, such as time of day or where food sources may be located. Animals take advantage of this prevalent and informative cue to make behavioral choices. However, the types of choices animals face depend greatly on their environments and needs at any given time. In particular, animals that undergo metamorphosis, with arthropods being the prime example, experience dramatic changes in both behavior and ecology, which in turn may require altering the structure and function of sensory systems such as vision. Amphibiotic organisms maintain aquatic lifestyles as juveniles before transitioning to terrestrial lifestyles as adults. However, light behaves differently in water than in air, resulting in distinct aquatic and terrestrial optical environments. Visual changes in response to these optical differences can occur on multiple levels, from corneal structure down to neural organization. In this review, we summarize examples of alterations in the visual systems of amphibiotic larval and adult insects and malacostracan crustaceans, specifically those attributed to environmental differences between metamorphic phases.

Proteolytic profile of larval developmental stages of Penaeus vannamei: An activity and mRNA expression approach

In arthropods, the cleavage of specific proteins by peptidases has pivotal roles in multiple physiological processes including oogenesis, immunity, nutrition, and parasitic infection. These enzymes are also key players in the larval development, and well-described triggers of molting and metamorphosis. In this work the peptidase complement throughout the larvae development of Penaeus vannamei was quantified at the transcript and activity level using qPCR and fluorogenic substrates designed to be hydrolyzed by class-specific peptidases respectively, providing a detailed identification of the proteolytic repertoire in P. vannamei larvae. Significant changes in the peptidase activity profile were observed. During the lecithotrophic naupliar instars, the dominant peptidase activity and expression derive from cysteine peptidases, suggesting that enzymes of this class hydrolyze the protein components of yolk as the primary amino acid source. At the first feeding instar, zoea, dominant serine peptidase activity was found where trypsin activity is particularly high, supporting previous observations that during zoea the breakdown of food protein is primarily enzymatic. At decapodid stages the peptidase expression and activity is more diverse indicating that a multienzyme network achieves food digestion. Our results suggest that proteolytic enzymes fulfill specific functions during P. vannamei larval development.

X-Ray Microscopy of the Larval Crustacean Brain

Micro-computed X-ray tomography (μCT) coupled with visualization techniques such as three-dimensional reconstruction of internal morphological structures has opened up new pathways for analyzing the anatomy of nervous systems in intact specimens. The possibility for combining μCT with other techniques is one of the major advantages of μCT scanning, and the technical development of higher resolutions in lab-based μCT-scanners allows for investigating the anatomy of specimens in the sub-milimeter range. The European shore crab Carcinus maenas features a larval development over four zoeal and one megalopal stage with body lengths ranging from 500 μm to 2000 μm. The developing nervous system in the larvae of C. maenas is organized into a central brain which is connected via esophageal connectives with a ventral nerve chord and segmental ganglia. Since soft tissues such as the nervous tissues feature low contrasts compared to other tissues such as muscles or cuticularized body parts, the interpretation in μCT scans is challenging and needs some practice. The protocol described here is also applicable for larger specimens of a variety of species and spans over 2-3 days resulting in an image stack ready for postprocessing and visualization.

Genetic structure and population connectivity of the blue and red shrimp Aristeus antennatus

The blue and red shrimp Aristeus antennatus is a demersal marine species harvested by bottom trawling in the Mediterranean Sea, the adjacent Atlantic Ocean (AO) waters, and the Mozambique Channel in the Indian Ocean (IO). As it is considered to be a priority species for sustainable fishing, identification of its genetic stocks and the connectivity between them is essential. Using 12 microsatellite loci we detected at least four genetic stocks distributed in the Western Mediterranean (WM), Eastern Mediterranean (EM), AO, and IO and signals for a possible fifth stock in the Alborán Sea. We detected no additional population structuring within the WM. Thus, although the Almería-Orán Front exerts some isolating effect, high genetic homogeneity and gene flow are present within the WM Basin. The IO stock is genetically closer to the AO stock than to the others; thus, the species dispersion route is more likely via the Atlantic Ocean than via the Red Sea. Large effective population sizes suggest population sustainability, but moderate genetic diversity values indicate to proceed with caution. Our genetic results serve as a basis for species conservation to ensure long-term sustainability of this marine resource.

Inducers of settlement and metamorphosis of the shrimp Hippolyte inermis Leach in Posidonia oceanica

Larvae of the caridean shrimp Hippolyte inermis persist in the plankton of the Mediterranean up to about one month. Since they need to reach appropriate coastal areas for their recruitment in seagrass meadows, we hypothesized that leaves of Posidonia oceanica or, alternatively, algae present in their epiphytic biofilms, might be physically recognised as target substrates and trigger larval metamorphosis and settlement. Chemical cues could improve the finding of suitable habitats for settlement. Thus, the effects of leaves of P. oceanica and biofilms of the diatom Cocconeis scutellum parva, seasonally abundant in the leaf epiphytic stratum, were investigated along with the effect of volatile organic compounds (VOCs) extracted from the epiphytic diatom. The physical induction with P. oceanica accelerated larval settlement, stimulating an earlier and faster metamorphosis of larvae. C. scutellum parva produced a weaker effect on settlement; however, diatom’s VOCs had evident influence and accelerated metamorphosis and settlement. We concluded that such chemical cues as the VOCs produced by epiphytic diatoms, reinforce the effect of physical cues for the identification of suitable settlement locations for this shrimp.

Food Restrictions Affect the Larval Metamorphosis and Early Juvenile Performance in a Neotropical Mangrove Fiddler Crab (Leptuca cumulanta)

Sporadic fluctuations in food availability may affect larval biology and post-metamorphic development in many marine invertebrates. In an experimental study in the laboratory, we investigated whether different regimes (1, 3, and 5 days) of initial starvation or feeding affect the survival and duration of the last planktotrophic larval stage (i.e., megalopa) of the neotropical mangrove fiddler crab Leptuca cumulanta. Newly metamorphosed crabs originating from megalopae starved for 1 and 3 days were cultured through the first 5 juvenile stages to further evaluate whether prior nutritional experience affects the post-larval performance of this species. All megalopae that were starved continuously died, while 80% of the larvae that were fed constantly metamorphosed successfully into the juvenile stage. Megalopae initially starved for 3 and 5 days exhibited lower survival (55% and 30% of larval metamorphosis, respectively) than larvae starved for only 1 day (85%) or fed constantly. The starvation periods (1, 3, and 5 days) also significantly prolonged the mean megalopal stage duration (12.8, 13.9, and 14.3 days, respectively) compared to the continuous feeding regime (10.6 days). Survival of the megalopae subjected to different periods of initial feeding (1, 3, and 5 days) was significantly lower (15.0%, 57.5%, and 62.5%, respectively) than survival of the larvae fed constantly. The mean megalopal stage duration, by contrast, did not vary among megalopae initially fed for 3 and 5 days or fed continuously (10.4 days). The larval starvation did not affect survival and carapace shape of juveniles, but it did alter their intermolt period, growth, and body size. These carryover effects were stronger in the first juvenile crab stage than in other juvenile stages. Our results indicate that the timing and duration of the starvation or feeding regime experienced by the megalopae may affect their successful survival and developmental period until metamorphosis to juvenile life. In addition, the preceding larval starvation associated with a prolonged larval period may also affect early juvenile performance in specific crab stages of L. cumulanta.

Eco-physiological responses of copepods and pteropods to ocean warming and acidification

We compare physiological responses of the crustacean copepod Calanus pacificus and pelagic pteropod mollusk Limacina helicina to ocean temperatures and pH by measuring biomarkers of oxidative stress, antioxidant defences, and the activity of the respiratory electron transport system in organisms collected on the 2016 West Coast Ocean Acidification cruise in the California Current System. Copepods and pteropods exhibited strong but divergent responses in the same habitat; copepods had higher oxygen-reactive absorbance capacity, glutathione-S-transferase, and total glutathione content. The ratio between reduced to oxidised glutathione was higher in copepods than in pteropods, indicating lower oxidative stress in copepods. Pteropods showed higher activities of glutathione reductase, catalase, and lipid peroxidation, indicating increased antioxidant defences and oxidative stress. Thus, the antioxidant defence system of the copepods has a greater capacity to respond to oxidative stress, while pteropods already face severe stress and show limited capacity to deal with further changes. The results suggest that copepods have higher adaptive potential, owing to their stronger vertical migration behaviour and efficient glutathione metabolism, whereas pteropods run the risk of oxidative stress and mortality under high CO₂ conditions. Our results provide a unique dataset and evidence of stress-inducing mechanisms behind pteropod ocean acidification responses.

Presence of a stridulatory apparatus in the manca stages of isopods (Crustacea, Isopoda, Oniscidea)

Armadilloofficinalis Duméril, 1816 (Armadillidae) is a widespread terrestrial isopod species in the Mediterranean basin and on the western coasts of the Black Sea. The species is adapted to live in xeric environments and has mainly nocturnal habits. This species is capable of producing stridulations, which is nowadays recognized as a synapomorphy of the genus. In both sexes, these vibrations are produced by a line of scales on the propodus of pereopod 4 and 5. The main goals of this study are: to describe the manca stages of Armadilloofficinalis; to detect the presence of the stridulatory apparatus in the manca stages; to evaluate the differences of such apparatus in the various manca stages. The manca stages (I, II, III) of Armadilloofficinalis are described for the first time showing: i, the shortest duration (known in literature) of the manca stage I (approximately 30 minutes); ii, the presence of a rudimental stridulatory organ that may be of great importance in terms of evolutionary aspects and adaptation to terrestrial life. Notes on the reproductive biology are also reported. Furthermore, some considerations on future perspectives for A.officinalis as a model species in biotremology are also discussed.

An atlas of larval organogenesis in the European shore crab Carcinus maenas L. (Decapoda, Brachyura, Portunidae)

BACKGROUND

The life history stages of brachyuran crustaceans include pelagic larvae of the Zoea type which grow by a series of moults from one instar to the next. Zoeae actively feed and possess a wide range of organ systems necessary for autonomously developing in the plankton. They also display a rich behavioural repertoire that allows for responses to variations in environmental key factors such as light, hydrostatic pressure, tidal currents, and temperature. Brachyuran larvae have served as distinguished models in the field of Ecological Developmental Biology fostering our understanding of diverse ecophysiological aspects such as phenotypic plasticity, carry-over effects on life-history traits, and adaptive mechanisms that enhance tolerance to fluctuations in environmental abiotic factors. In order to link such studies to the level of tissues and organs, this report analyses the internal anatomy of laboratory-reared larvae of the European shore crab Carcinus maenas. This species has a native distribution extending across most European waters and has attracted attention because it has invaded five temperate geographic regions outside of its native range and therefore can serve as a model to analyse thermal tolerance of species affected by rising sea temperatures as an effect of climate change.

RESULTS

Here, we used X-ray micro-computed tomography combined with 3D reconstruction to describe organogenesis in brachyuran larvae. We provide a detailed atlas of the larval internal organization to complement existing descriptions of its external morphology. In a multimethodological approach, we also used cuticular autofluorescence and classical histology to analyse the anatomy of selected organ systems.

CONCLUSIONS

Much of our fascination for the anatomy of brachyuran larvae stems from the opportunity to observe a complex organism on a single microscopic slide and the realization that the entire decapod crustacean bauplan unfolds from organ anlagen compressed into a miniature organism in the sub-millimetre range. The combination of imaging techniques used in the present study provides novel insights into the bewildering diversity of organ systems that brachyuran larvae possess. Our analysis may serve as a basis for future studies bridging the fields of evolutionary developmental biology and ecological developmental biology.

Cuticle morphogenesis in crustacean embryonic and postembryonic stages

The crustacean cuticle is a chitin-based extracellular matrix, produced in general by epidermal cells and ectodermally derived epithelial cells of the digestive tract. Cuticle morphogenesis is an integrative part of embryonic and postembryonic development and it was studied in several groups of crustaceans, but mainly with a focus on one selected aspect of morphogenesis. Early studies were focused mainly on in vivo or histological observations of embryonic or larval molt cycles and more recently, some ultrastructural studies of the cuticle differentiation during development were performed. The aim of this paper is to review data on exoskeletal and gut cuticle formation during embryonic and postembryonic development in crustaceans, obtained in different developmental stages of different species and to bring together and discuss different aspects of cuticle morphogenesis, namely data on the morphology, ultrastructure, composition, connections to muscles and molt cycles in relation to cuticle differentiation. Based on the comparative evaluation of microscopic analyses of cuticle in crustacean embryonic and postembryonic stages, common principles of cuticle morphogenesis during development are discussed. Additional studies are suggested to further clarify this topic and to connect the new knowledge to related fields.

Developmental Transcriptomics of the Hawaiian Anchialine Shrimp Halocaridina rubra Holthuis, 1963 (Crustacea: Atyidae)

Many crustacean species progress through a series of metamorphoses during the developmental transition from embryo to adult. The molecular genetic basis of this transition, however, is not well characterized for a large number of crustaceans. Here, we employ multiple RNA-Seq methodologies to identify differentially expressed genes (DEGs) between "early" (i.e., Z₁ - Z₂) as well as "late" (i.e., Z₃ - Z₄) larval and adult developmental stages of Halocaridina rubra Holthuis (1963), an atyid shrimp endemic to the environmentally variable anchialine ecosystem of the Hawaiian Islands. Given the differences in salinity tolerance (narrow vs. wide range), energy acquisition (maternal yolk-bearing vs. microphagous grazing), and behavior (positively phototactic vs. not) between larvae and adults, respectively, of this species, we hypothesized the recovery of numerous DEGs belonging to functional categories relating to these characteristics. Consistent with this and regardless of methodology, hundreds of DEGs were identified, including upregulation of opsins and other light/stimulus detection genes and downregulation of genes related to ion transport, digestion, and reproduction in larvae relative to adults. Furthermore, isoform-switching, which has been largely unexplored in crustacean development, appears to be pervasive between H. rubra larvae and adults, especially among structural and oxygen-transport genes. Finally, by comparing RNA-Seq methodologies, we provide recommendations for future crustacean transcriptomic studies, including a demonstration of the pitfalls associated with identifying DEGs from single replicate samples as well as the utility of leveraging "prepackaged" bioinformatics pipelines.

Larval descriptions of the family Porcellanidae: A worldwide annotated compilation of the literature (Crustacea, Decapoda)

For most of the family Porcellanidae, which comprises 283 species, larval development remains to be described. Full development has been only described for 52 species, while part of the larval cycle has been described for 45 species. The importance of knowing the complete larval development of a species goes beyond allowing the identification of larval specimens collected in the plankton. Morphological larval data also constitute a support to cladistic techniques used in the establishment of the phylogenetic status (see Hiller et al. 2006, Marco-Herrero et al. 2013). Nevertheless, the literature on the larval development of this family is old and widely dispersed and in many cases it is difficult to collect the available information on a particular taxon. Towards the aim of facilitating future research, all information available on the larval development of porcellanids has been compiled. Following the taxonomic checklist of Porcellanidae proposed by Osawa and McLaughlin (2010), a checklist has been prepared that reflects the current knowledge about larval development of the group including larval stages and the method used to obtain the larvae, together with references. Those species for which the recognised names have been changed according to Osawa and McLaughlin (2010) are indicated.

Redefining metamorphosis in spiny lobsters: molecular analysis of the phyllosoma to puerulus transition in Sagmariasus verreauxi

The molecular understanding of crustacean metamorphosis is hindered by small sized individuals and inability to accurately define molt stages. We used the spiny lobster Sagmariasus verreauxi where the large, transparent larvae enable accurate tracing of the transition from a leaf-shaped phyllosoma to an intermediate larval-juvenile phase (puerulus). Transcriptomic analysis of larvae at well-defined stages prior to, during, and following this transition show that the phyllosoma-puerulus metamorphic transition is accompanied by vast transcriptomic changes exceeding 25% of the transcriptome. Notably, genes previously identified as regulating metamorphosis in other crustaceans do not fluctuate during this transition but in the later, morphologically-subtle puerulus-juvenile transition, indicating that the dramatic phyllosoma-puerulus morphological shift relies on a different, yet to be identified metamorphic mechanism. We examined the change in expression of domains and gene families, with focus on several key genes. Our research implies that the separation in molecular triggering systems between the phyllosoma-puerulus and puerulus-juvenile transitions might have enabled the extension of the oceanic phase in spiny lobsters. Study of similar transitions, where metamorphosis is uncoupled from the transition into the benthic juvenile form, in other commercially important crustacean groups might show common features to point on the evolutionary advantage of this two staged regulation.

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.

Roles of small RNAs in the immune defense mechanisms of crustaceans

Small RNAs, 21-24 nucleotides in length, are non-coding RNAs found in most multicellular organisms, as well as in some viruses. There are three main types of small RNAs including microRNA (miRNA), small-interfering RNA (siRNA), and piwi-interacting RNA (piRNA). Small RNAs play key roles in the genetic regulation of eukaryotes; at least 50% of all eukaryote genes are the targets of small RNAs. In recent years, studies have shown that some unique small RNAs are involved in the immune response of crustaceans, leading to lower or higher immune responses to infections and diseases. SiRNAs could be used as therapy for virus infection. In this review, we provide an overview of the diverse roles of small RNAs in the immune defense mechanisms of crustaceans.

Differential habitat use by demographic groups of the redfinger rubble crab Eriphia gonagra (Fabricius, 1781)

The structurally diverse rocky shores along the northern coast of the state of São Paulo, Brazil, support a varied fauna and provide refuges for many organisms. Some of these environments allow for extensive microhabitats, among them the sand reefs formed by the polychaete Phragmatopoma lapidosa, which occupy much of this area. The beauty of the landscape attracts large numbers of tourists, who contribute to the damage to the sand reef colonies, causing an imbalance in the patterns of population distribution and of this ecosystem. We describe the structure and population biology of the redfinger rubble crab Eriphia gonagra, and investigated the differential occupation of the habitat by each demographic category of this species. Crabs were sampled monthly for two consecutive years on the rocky coast of Grande Beach, Ubatuba, São Paulo, during spring low tides. Sampling was carried out over an area of approximately 1200 m2, during two hours on the rock surface and another two hours on the sand reefs. A total of 1407 crabs were collected; 776 on the sand reef (SR) and 631 on the rocky shore (RO). The majority of juvenile crabs inhabited the SR, while adult crabs were equally distributed in both microhabitats. This study showed that the SR is a natural nursery ground for the establishment of the early juvenile stages of E. gonagra, which use the reefs as a refuge and food resource. Many other organisms (mollusks, echinoderms, polychaetes etc.) settle on the reefs, and these areas may be among the most important in maintaining benthic diversity in the region.

Field assessment of the predation risk-food availability trade-off in crab megalopae settlement

Settlement is a key process for meroplanktonic organisms as it determines distribution of adult populations. Starvation and predation are two of the main mortality causes during this period; therefore, settlement tends to be optimized in microhabitats with high food availability and low predator density. Furthermore, brachyuran megalopae actively select favorable habitats for settlement, via chemical, visual and/or tactile cues. The main objective in this study was to assess the settlement of Metacarcinus edwardsii and Cancer plebejus under different combinations of food availability levels and predator presence. We determined, in the field, which factor is of greater relative importance when choosing a suitable microhabitat for settling. Passive larval collectors were deployed, crossing different scenarios of food availability and predator presence. We also explore if megalopae actively choose predator-free substrates in response to visual and/or chemical cues. We tested the response to combined visual and chemical cues and to each individually. Data was tested using a two-way factorial design ANOVA. In both species, food did not cause significant effect on settlement success, but predator presence did, therefore there was not trade-off in this case and megalopae respond strongly to predation risk by active aversion. Larvae of M. edwardsii responded to chemical and visual cues simultaneously, but there was no response to either cue by itself. Statistically, C. plebejus did not exhibit a differential response to cues, but reacted with a strong similar tendency as M. edwardsii. We concluded that crab megalopae actively select predator-free microhabitat, independently of food availability, using chemical and visual cues combined. The findings in this study highlight the great relevance of predation on the settlement process and recruitment of marine invertebrates with complex life cycles.

Determination of extremely high pressure tolerance of brine shrimp larvae by using a new pressure chamber system

Hydrostatic pressure is the only one of a range of environmental parameters (water temperature, salinity, light availability, and so on) that increases in proportion with depth. Pressure tolerance is therefore essential to understand the foundation of populations and current diversity of faunal compositions at various depths. In the present study, we used a newly developed pressure chamber system to examine changes in larval activity of the salt-lake crustacean, Artemia franciscana, in response to a range of hydrostatic pressures. We showed that A. franciscana larvae were able to survive for a short period at pressures of ≤ 60 MPa (approximately equal to the pressure of 6000 m deep). At a pressure of > 20 MPa, larval motor ability was suppressed, but not lost. Meanwhile, at a pressure of > 40 MPa, some of the larval motor ability was lost without recovery after decompression. For all experiments, discordance of movement and timing between right and left appendages, was observed at pressures of > 20 MPa. Our results indicate that the limit of pressure for sustaining active behavior of A. franciscana larvae is ∼20 MPa, whereas the limit of pressure for survival is within the range 30-60 MPa. Thus, members of the genus Artemia possess the ability to resist a higher range of pressures than their natural habitat depth. Our findings demonstrated an example of an organism capable of invading deeper environment in terms of physical pressure tolerance, and indicate the need and importance of pressure study as an experimental method.

The reaction of European lobster larvae (Homarus gammarus) to different quality food: effects of ontogenetic shifts and pre-feeding history

Young larval stages of many organisms represent bottlenecks in the life-history of many species. The high mortality commonly observed in, for example, decapod larvae has often been linked to poor nutrition, with most studies focussing on food quantity. Here, we focus instead on the effects of quality and have investigated its effects on the nutritional condition of lobster larvae. We established a tri-trophic food chain consisting of the cryptophyte Rhodomonas salina, the calanoid copepod Acartia tonsa and larvae of the European lobster Homarus gammarus. In a set of experiments, we manipulated the C:N:P stoichiometry of the primary producers, and accordingly those of the primary consumer. In a first experiment, R. salina was grown under N- and P-limitation and the nutrient content of the algae was manipulated by addition of the limiting nutrient to create a food quality gradient. In a second experiment, the effect on lobster larvae of long- and short-term exposure to food of varying quality during ontogenetic development was investigated. The condition of the lobster larvae was negatively affected even by subtle N- and P-nutrient limitations of the algae. Furthermore, younger lobster larvae were more vulnerable to nutrient limitation than older ones, suggesting an ontogenetic shift in the capacity of lobster larvae to cope with low quality food. The results presented here might have substantial consequences for the survival of lobster larvae in the field, as, in the light of future climate change and re-oligotrophication of the North Sea, lobster larvae might face marked changes in temperature and nutrient conditions, thus significantly altering their condition and growth.

The implications of temperature-mediated plasticity in larval instar number for development within a marine invertebrate, the shrimp Palaemonetes varians

Variations in larval instar number are common among arthropods. Here, we assess the implications of temperature-mediated variations in larval instar number for larval development time, larval growth rates, and juvenile dry weight within the palaemonid shrimp, Palaemonetes varians. In contrast with previous literature, which focuses on terrestrial arthropods, particularly model and pest species often of laboratory lines, we use wild shrimp, which differ in their life history from previous models. Newly-hatched P. varians larvae were first reared at 5, 10, 17, 25, and 30°C to assess their thermal scope for development. Larvae developed at 17, 25, and 30°C. At higher temperatures, larvae developed through fewer larval instars. Two dominant developmental pathways were observed; a short pathway of four instars and a long pathway of five instars. Longer developmental pathways of six to seven instars were rarely observed (mostly at lower temperatures) and consisted of additional instars as ‘repeat’ instars; i.e. little developmental advance over the preceding instar. To assess the implications of temperature-mediated variation in larval instar number, newly-hatched larvae were then reared at 15, 20, and 25°C. Again, the proportion of larvae developing through four instars increased with temperature. At all temperatures, larval development time and juvenile dry weight were greater for larvae developing through five instars. Importantly, because of the increasing proportion of larvae developing through four instars with increasing temperature, larval traits associated with this pathway (reduced development time and juvenile dry weight) became more dominant. As a consequence of increasing growth rate with temperature, and the shift in the proportion of larvae developing through four instars, juvenile dry weight was greatest at intermediate temperatures (20°C). We conclude that at settlement P. varians juveniles do not follow the temperature-size rule; this is of importance for life-history ecology in response to environmental change, as well as for aquaculture applications.

Nervous systems in 3D: a comparison of Caridean, anomuran, and brachyuran zoea-I (Decapoda)

Using serial semi-thin sections and digital 3D-reconstructions we studied the nervous systems of zoea-I larvae in three decapod species, Hippolyte inermis (Leach, 1815), Porcellana platycheles (Pennant, 1777), and Pachygrapsus marmoratus (Fabricius, 1787). These taxa represent three decapod lineages, that is, Caridea, Anomura, and Brachyura, each characterized by specific zoea-I morphology. Special attention was paid to development of ganglia, neuropil composition, and segmental nerves. In all zoeae studied, the overall elements, for example, the segmental ganglia, their neuropils and most of the nerves of the adult decapod nervous system are present. Ongoing differentiation processes are observable as well, most obvious in segments with well-developed limbs the ganglia are in a more advanced stage of differentiation and more voluminous compared to segments with only limb buds or without externally visible limb anlagen. Intra- and interspecific comparisons indicate that neuromere differentiation thus deviates from a simple anterior-posterior gradient as, for example, posterior thoracic neuromeres are less developed than those of the pleon. In addition, the differences in the progress of the development of ganglia between the studied taxa can best be attributed to heterochronic mechanisms. Taxon and stage-specific morphologies indicate that neuronal architecture reflects both, morphogenesis to the adult stage and specific larval adaptions, and provides sets of characters relevant to understanding the corresponding phylogeny.

Analysis of gene expression in Homarus americanus larvae exposed to sublethal concentrations of endosulfan during metamorphosis

Agricultural pesticide runoff has been suspected as the cause of numerous fish kills in rivers throughout Prince Edward Island but the impact on the surrounding marine environment is unknown. Endosulfan, an organochlorine pesticide, is a potent neurotoxin and molt inhibitor used to combat the Colorado potato beetle however it has the potential to affect non-target organisms including the American lobster (Homarus americanus). Metamorphosis is a critical stage of development and the effects of contaminant exposure during this time are largely unknown in lobster. A 14day endosulfan exposure was performed to identify the effects on survival, development and gene expression in lobster larvae during metamorphosis; all of which were predicted to be negatively impacted. The higher endosulfan concentrations resulted in greater mortality and a significant increase in the number of days required to reach metamorphosis in surviving animals. A custom made H. americanus microarray was used for monitoring the changes in expression of 14,592 genes at the termination of the exposure. Genes with >1.5 fold change and identified as being significant at p<0.05 using one-way ANOVA were selected for further analysis. A total of 707 genes were identified as being significantly differentiated, however with only ~40% annotation of the array, the majority of these genes were unknown. Annotated genes of interest were involved in many processes: development, metabolism, immunity and oxidative stress response and gene regulation. Nine genes of interest (histone H1, farnesoic acid O-methyltransferase, cuticle protein, glutathione S-transferase, thioredoxin, NADH dehydrogenase, ecdysone nuclear receptor Fushi tarazu F1 (FTZ-F1), ferritin and ecdysone inducible protein E75 (EIP-E75)) were selected for RT-qPCR validation of the microarray results. The RT-qPCR method was more sensitive than the microarray yet detected similar expression patterns. The two highest endosulfan concentrations resulted in increased mortalities, developmental delays in reaching metamorphosis and significant changes in gene expression. This research provides a foundation for using microarray gene expression profiles as screening tools for exploring the impact of environmental contaminants on lobster.

Brachyuran and anomuran crabs associated with Schizoporella unicornis (Ectoprocta, Cheilostomata) from southeastern Brazil

The main goals of this investigation were to describe the community structure of anomuran and brachyuran crabs inhabiting reefs constituted by colonies of Schizoporella unicornis, and to provide a species importance ranking for this community. Collections were carried out on S. unicornis reefs at two-month intervals from May 2003 to May 2004, in the rocky sublittoral of the southeastern Brazilian coast. Relative abundance and occurrence were used to rank these species in the hierarchy importance. A total of 2,018 individuals were obtained, in 11 families, 22 genera and 31 species. Porcellanidae and Pilumnidae were the most abundant families, comprising respectively almost 60% and 15% of individuals sampled. The species ranking indicated four main groups A, B, C and D, with group A subdivided. Subgroup A1 contained 9 species, including the species of greatest ecological importance for community regarding abundance and occurrence. The great abundance of crabs associated with S. unicornis seems to be the result of its recognized importance during the crab developmental cycle, and as shelter and food for some Decapod species. These observations reveal the importance of conserving the areas occupied by these reef colonies, which appear to be an important environment for maintaining local biodiversity.