Explanations for the coexistence of many closely related species in inland waters continue to be generated more than 50 years after Hutchinson's question: why are there so many kinds of animals? This ...review focuses on the hypothesis that high species diversity of freshwater gastropods results, in part, from predators maintaining biodiversity across a range of deep- and shallow-water habitats. Invertebrate predators, such as aquatic insects, and leeches consume soft tissue of pulmonate snails by penetrating shells of various shapes and sizes. Crayfish and large prawns chip around the shell aperture to enter thick shells and crush small shells with their mandibles. Crabs use their strong chelae to crush thin and thick shells. Fishes with pharyngeal teeth are major shell-breaking predators that combine with other vertebrate predators such as turtles and wading birds to increase the diversity of gastropod communities by regulating the abundance of dominant species. Although the generalized diets of most freshwater predators preclude tight co-evolutionary patterns of responses, there are combinations of predators that modify gastropod behavior and shell morphology in aquatic assemblages of different ages and depths. This combination of invertebrate and vertebrate predatory impacts led to competitive advantages among individual gastropods with different adaptations: (1) less vulnerable shell morphologies and sizes; (2) predator-avoidance behaviors; or (3) rapid and widespread dispersal with variable life histories. Some individuals develop thicker and/or narrow-opening shells or shells with spines and ridges. Other thin-shelled species crawl out of the water or burrow to lower their risk to shell-breaking or shell-entering predators. Some alter their age at first reproduction and grow rapidly into a size refuge. Fluctuations in water levels and introductions of non-native species can change competitive dominance relationships among gastropods and result in major losses of native species. Many different gastropod predators control species that are human disease vectors. Most snails and their predators provide other ecosystem services such as nutrient cycling and transfer of energy to higher trophic levels. Their persistence and diversity of native species require adaptive management and coordinated study.
Studies on food web structure in estuaries based on stable isotopes have usually not taken spatiotemporal variations in the isotopic variability of food web components into account. We investigated ...temporal and between-habitat variations in the isotopic composition (13C/12C and 15N/14N) of basal food sources—i.e. primary producers, particulate organic matter (POM) in the sediment or in suspension, and biofilm—and consumers and explored their implications for food web structure and dynamics. Samples of 9 basal sources (N = 224) and 6 representative invertebrates and fish (N = 303) were collected monthly over 1 yr in a marsh creek and a mudflat of the Patos Lagoon, a large southwestern Atlantic estuary. The relative contributions of food sources to consumers were estimated by mixing models. Overall, δ13C values of food sources and consumers were higher (p < 0.05) in the mudflat, whereas δ15N values were enriched (p < 0.05) in the marsh creek for most primary producers and consumers. C and N isotope values varied on both monthly and seasonal scales, with several food sources and consumers exhibiting higher values (p < 0.05) during the spring and summer. The primary food sources were POM in the sediment, C₄ plants (e.g. widgeon grass), and, to a lesser extent, suspended POM. Biofilm and macroalgae were also food sources for consumers in the marsh creek and mudflat, respectively, especially during warmer seasons. Our findings corroborate the hypothesis that the Patos lagoon food web is spatially structured and supported by local basal sources and detritus of different origins, which can be seasonally important for consumers in each particular habitat.
To maximise productivity, a better understanding of the underlying causes of subfertility that lead to inferior offspring and high mortality is imperative. In decapod crustaceans, most research has ...focused on female reproductive performance, with little attention given to male fertility. Paternal genetic contribution is critical to both successful embryonic and post‐embryonic development. Assessment of sperm quality can be a direct method to determine male subfertility in decapods. Sperm quality parameters such as sperm concentration and morphology have traditionally been used to determine male reproductive performance, but these procedures are time‐consuming and can only assess a limited number of sperm cells and males. Alternative diagnostic biomarkers used widely in humans and other mammals could be adapted to decapod crustaceans and may be more indicative of sperm fertilisation competence and male reproductive performance. These predictive biomarkers use fluorescent cellular dyes and high‐throughput flow cytometry or computer‐assisted sperm microscopic analysis to evaluate sperm viability, mitochondrial function, acrosome reaction and DNA fragmentation. This review examines current and advanced biomarkers to evaluate sperm quality and further explores state‐of‐the‐art procedures of sperm cryopreservation (conventional vs. vitrification techniques) and artificial fertilisation in decapod crustaceans. Sperm freezing coupled with artificial fertilisation in decapods permits the long‐term storage, controlled timing and selection of individuals for reproduction. Collectively, these tools can be applied to commercial broodstock management to improve productivity and accelerate selective breeding in the crustacean aquaculture industry.
A new alpheid shrimp genus, Pachelpheus gen. nov., is established to accommodate Pachelpheus pachyacanthus sp. nov., described based on two specimens from the Las Perlas Archipelago, Pacific coast of ...Panama. Pachelpheus pachyacanthus sp. nov. appears to be an obligate symbiont dwelling in burrows of yet unknown infaunal hosts, on shallow near-shore subtidal sand flats. The main morphological characters of Pachelpheus gen. nov. are: (1) frontal margin of carapace with broadly rounded rostral projection, without orbital teeth; (2) sixth pleonite with articulated plate; (3) telson with two pairs of cuspidate setae dorsally, without anal tubercles; (4) eyes concealed in dorsal view, partly visible in lateral view; (5) chelipeds equal in size, symmetrical in shape, moderately enlarged, stout, carried extended; (6) cheliped carpus without rows of setae mesially; (7) cheliped fingers without snapping mechanism, each finger armed with one stout tooth; (8) second pereiopod carpus with five sub-articles; (9) third, fourth and fifth pereiopods with ischia armed with single robust cuspidate seta, meri armed with one to several unusually robust cuspidate setae; (10) second pleopod with appendix masculina in males only; (11) uropodal exopod and endopod with rows of slender spiniform setae on their distal margins; (12) uropodal diaeresis unusually thickened laterally, with two very stout spiniform setae; and (13) lateral lobe of the uropodal protopod rounded. The new genus appears to be morphologically most similar to Jengalpheops Anker Dworschak, 2007 and Leslibetaeus Anker, Poddoubtchenko Wehrtmann, 2006.
This study reports on the prevalence and severity of infections caused by the parasitic dinoflagellate, Hematodinium in juvenile edible crabs (Cancer pagurus) found in 2 intertidal survey sites ...(Mumbles Head and Oxwich Bay) in the Bristol Channel, UK. Crabs were assessed for the presence and severity of Hematodinium infections by the histological examination of infected tissues. Such infections were found to exhibit a seasonal trend in the 2 study areas with high numbers of animals (ca. 30%) infected in the spring to summer but with low severity. Conversely, in November only ca. 10% of crabs were infected but these animals had large numbers of parasites in their haemolymph and other tissues. At this time, the carapace and underlying tissues of infected crabs had the chalky, pinkish-orange appearance that is characteristic of this disease. Hematodinium-infected crabs ranged in size from 12 to 74 mm carapace width. Overall, it is concluded that the high prevalence of infection of juvenile crabs in this area may have implications for the sustainability of the edible crab fishery in the Bristol Channel.
Environmental gradients between marine biogeographical provinces separate distinct faunal communities. However, the absence of absolute dispersal barriers allows numerous species to occur on both ...sides of such boundaries. While the regional populations of such widespread species are often morphologically indistinguishable from each other, genetic evidence suggests that they represent unique ecotypes, and likely even cryptic species, that may be uniquely adapted to their local environment. Here, we explored genomic divergence in four sympatric southern African decapod crustaceans whose ranges span the boundary between the cool-temperate west coast (south-eastern Atlantic) and the warm-temperate south coast (south-western Indian Ocean) near the southern tip of the African continent. Using genome-wide data, we found that all four species comprise distinct west coast and south coast ecotypes, with molecular dating suggesting divergence during the Pleistocene. Transcriptomic data from the hepatopancreas of twelve specimens of one of these species, the mudprawn Upogebia africana, which were exposed to either 10 °C or 20 °C, showed a clear difference in gene expression profiles between the west- and south coast ecotypes. This difference was particularly clear at 10 °C, where individuals from the south coast experienced a ‘transcriptomic shock’. This low temperature is more typical of the west coast during upwelling events, and the physiological stress experienced by the south coast ecotype under such conditions may explain its absence from that coastline. Our results shed new light on the processes involved in driving genomic divergence and incipient speciation along coastlines with porous dispersal barriers.
The aim of this study was to assess the regulatory process of digestive peptidases of crustaceans in the presence of soybean trypsin inhibitor (SBTI). This naturally occurring inhibitor in soybean ...meal was used to inhibit the activity of digestive serine peptidases of the whiteleg shrimp Litopenaeus vannamei. In vitro, SBTI inhibited the total proteolytic activity and chymotrypsin activity by 65%. Trypsin activity was reduced by SBTI from 40% to 15% from 2 to 4 hr of incubation, which is the average time of residence of feed in the shrimp digestive system. During the bioassays, experimental groups were fed with increasing concentration of supplemental SBTI (1 g kg−1 and 2 g kg−1) and digestive gland and faeces of individual specimens were collected daily. At the end of the bioassay, peptidase activity of digestive gland and faeces was shown, revealing differential inhibition after feeding for 5 days. Several serine peptidases were observed in zymograms, showing a compensation effect on the digestive gland through the activation of peptidases from different catalytic type. These results provide evidence that the shrimp digestive gland can overcome the effect of SBTI by two adaptive mechanisms: synthesis of additional peptidases of the serine class and other unidentified peptidases.
Pleuroncodes monodon from the Chilean coast has seasonal reproduction. During the seasonal period, females and their eggs are exposed to seasonal variation in environmental conditions. In P. monodon ...populations inhabiting the Southern Pacific coast near Concepción, Chile, we quantified late summer (February-March 2014) and late winter (August-September 2014) seasonal variations in female reproductive parameters (carapace length, fecundity, reproductive output (RO), ash weight, organic content) as well as eggs parameters (length, volume, dry weight, organic content). There was conspicuous seasonal variation in the main reproductive parameters of this species. During the summer, the number of eggs and organic content of females were higher than winter, whereas RO was slightly higher in winter than in summer. Significant variation in the size and biomass of the eggs was also found between seasons. For example, eggs laid in summer were smaller, had a lower measured dry mass, and had a lower organic content than eggs laid in winter. Seasonal variations in the fecundity and size of the eggs have implications for fishery models, which can be used to estimate the relative contribution of different cohorts to recruitment and stability of adult benthic populations.
Biofilms are sticky exopolymer matrices with embedded microorganisms that form on virtually all submerged surfaces. Depending on the context, biofilms are beneficial or detrimental to macroorganisms. ...Two groups of decapod crustaceans, sand fiddler crabs (Uca pugilator) and blue crabs (Callinectes sapidus), were investigated to test whether externally secreted enzymes were present and if they were used to remove or prevent biofilm formation in the environment and on their surfaces. Three hydrolytic enzymes were of interest because of their ability to degrade biofilm components: amylase, trypsin and lysozyme. The role of these enzymes was investigated in two contexts, removal of biofilms from the environment for food detection and processing and prevention of biofilm formation on the macroorganism surface itself. To test this, enzyme activity was measured on feeding appendages of fiddler crabs, which feed on biofilms, and on egg masses externally brooded by blue crabs. All three enzyme activities were found on feeding appendages of fiddler crabs and in egg masses of blue crabs. For the context of removal of biofilms from the environment, the combined data of the enzymes present in fiddler crab saliva and the high diatom extraction efficiency (60–90% removal in less than 9s), suggests a role in separation of organic content from sand particles. Secondly, the data of enzymes present on fiddler crab legs (the main location of their chemoreceptors) and that leg exposure to a human amylase inhibitor significantly decreased fiddler crab feeding responses, suggests a role of the enzymes on fiddler crab legs in generating phagostimulants. For the context of prevention of microfouling, it was found that the same enzymes are present in blue crab egg mass fluids and that the activity levels increase as the eggs mature, particularly amylase, which increased dramatically in clutches with late stage embryos. These findings of enzymes present in egg mass fluid throughout maturation inform a large body of work on pheromones and hatching cues for blue crabs. Detachment of brooded eggs and incubation with enzymes at levels found in egg masses resulted in survival and hatching while detachment without addition resulted in death. These findings suggest that the same suite of enzymes is important to biochemically manage biofilms in two ecologically relevant contexts. Biochemical management of biofilms may be more prevalent in macroorganisms than previously thought.
•We probed two groups of crustaceans, fiddler crabs and blue crabs, for externally secreted enzymes involved in degradation of biofilm components, including: carbohydrates (by amylase), protein (by trypsin) and bacteria (by lysozyme).•All three enzymes were present on fiddler crab feeding appendages including dactyls and buccal secretions and found in blue crab egg masses throughout their development.•This work shows two examples of semi—terrestrial and aquatic organisms using the same suite of enzymes for biofilm removal in the different contexts of feeding and fouling management.
Latent phenoloxidase activity of hemocyanin (Hc) in whiteleg shrimp Penaeus vannamei was assayed to determine its potential involvement in postmortem melanosis. Conversion of pure 12-mer, but not ...6-mer, hemocyanin to phenoloxidase by endogenous (serine proteinases) and exogenous (SDS) effectors demonstrated the need of complex aggregation for displaying enzyme activity. Because Hc was converted to Hc-phenoloxidase (HcPO) by hemocytes extracts, the mechanism of conversion seems to be the same for polyphenoloxidases. HcPO has similar biochemical and kinetic properties as real polyphenoloxidases and uses mono- and diphenols as substrates. The kinetics of hydroxygenation of monophenols has a lag phase, typical for tyrosinases, contrary to oxidation of diphenols. Regardless of the structure of the substrate, melanin is finally formed. Because of the abundance, distribution, and resistance of Hc to freezing−thawing, involvement of Hc in black spot formation postmortem is suggested. This has important implications for commercialization of shrimp and related seafood.
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