Abstract The thermal responses and tolerance of organisms can be influenced by synergistic interactions with other environmental stresses. Although the heat sensitivity of the whiteleg shrimp (Penaeus vannamei Boone, 1931 = Litopenaeus vannamei) has been extensively researched, little is known about how hypoxia impacts the thermal tolerance of the species. We assessed the thermotolerance of P. vannamei postlarvae under combined hyperthermia and hypoxia conditions. Simultaneous hypoxia significantly decreased the thermotolerance (LT50) of the postlarvae at temperatures close to the upper thermal limit of the species.

Abstract We characterized the digestive enzymes in adults of Macrobrachium americanum (Spence Bate, 1868) in southeastern Mexico. The digestive enzyme extracts were made from the specimens’ hepatopancreas. Alkaline proteases, trypsin, chymotrypsin, carboxypeptidase A, leucine aminopeptidase, lipases, α-amylase and alkaline phosphatase activities were determined, as well as the percentage of inhibition, pH, and temperature stabilities through biochemical and electrophoretic techniques. The maximum digestive activity of proteases was at 35 °C and pH 11. Alkaline digestive proteases were highly stable at pHs 4, 9 and 11 at 55 °C after 30 min pre-incubation. PMSF inhibited two bands with proteolytic activity (35.1 and 23.2 kDa), and SBT1 inhibited all bands, including the one with the highest molecular weight (64.2 kDa). We concluded that enzymes in M. americanum coincide with those of omnivorous decapods with a tendency to carnivory.

Abstract Trophic discrimination or fractionation factors (TDFs), such as ∆15N and ∆13C, are used in stable isotope mixing models to account for differences between source tissues (diet/prey) and consumer tissues (predator). We aimed firstly to obtain TDF values for a spiny lobster, the southern rock lobster Jasus edwardsii (Hutton, 1875), to better understand lobster diet in the wild and secondly to investigate variability in isotope signature within tissues of individuals and across a temporal scale to test if non-lethal sampling can be used in an ecological context. We conducted an 18-mo captive feeding trial with juvenile lobsters using three diet treatments and analysed dorsal and leg muscle, along with dorsal and leg exoskeleton for δ13C and δ15N values. Average TDFs for the three diet treatments were 3.86 ± 0.98‰ (∆13C) and 5.06 ± 0.65‰ (∆15N) for leg muscle, and 4.45 ± 1.04‰ (∆13C) and 4.36 ± 0.6‰ (∆15N) for dorsal muscle. When tested against wild lobsters and prey, these TDFs outperformed multi-taxa TDFs found in the literature. Isotope values from lobster leg muscle were not identical to associated dorsal muscle but the two were highly correlated, indicating that non-lethal sampling is acceptable. Values for exoskeleton isotope were significantly different from muscle, likely due to the exoskeleton not being in a constant state of growth and replacement, unlike the muscle tissue, which constantly incorporates new material. We conclude that our experimentally derived TDFs are suitable for mixing model analysis for J. edwardsii and when tested on a wild sample of lobsters they outperformed other TDFs reported in the literature. We show that non-lethal sampling using leg muscle is an appropriate sampling method, since this tissue is highly correlated to the commonly used dorsal muscle. This option for non-lethal sampling enhances the potential to widely sample wild populations or sample during industrial processing without the need to sacrifice whole animals.

Abstract Traditional methods to study precopulatory mate guarding in Hyalella azteca (Saussure, 1858) have some limitations because precopulatory pairs are usually observed in isolation. This condition precludes researchers from testing the role of the social environment in the duration of precopulatory mate guarding. We present the use of a sampling method to investigate the influence of sex ratios on guarding success (the proportion of precopulatory pairs per trial) in mixed-sex groups of H. azteca. The presence/absence of precopulatory pairs over eight consecutive days, morning and afternoon samplings, was analysed as a series of successes (runs) to estimate the mean precopula duration. The non-random nature of the observed duration of the precopula was tested against a probabilistic distribution based on the set of all ways every possible duration may occur. While skewed sex ratios increased guarding success of the rarest sex, even sex ratios decreased it. The mean duration of observed precopulas (2.32 and 2.08 d for the morning and afternoon periods, respectively) is consistent with theoretical and empirical results, which confirms the accuracy and usefulness of the sampling method we used. The use of this method and the associated probabilistic analysis of the relevant data can enhance the study of the effect of biotic and abiotic factors on precopulatory mate guarding. It can also be used to test predictions derived from hypothesis concerned with mate guarding among crustaceans.

Abstract Mutations may lead to the evolution and diversification of color phenotypes in animals. Much of the research on this topic, however, has been conducted on vertebrates. I compile here records of color variants in freshwater crayfishes (Decapoda: Astacidea). I found color variants to be surprisingly common, with 115 documented occurrences. The overwhelming majority of these variants were blue-colored (71.3%), although there are records of document red and orange variants, among others. Whether these variants are all due to mutations or can lead to adaptive evolution in crayfishes is unknown. Some crayfish species exhibit conspicuous colors like blue, orange, and red in nature. Many of these conspicuously colored species are also semi-terrestrial burrowers, which have limited migration potential, smaller population sizes, and thus reduced gene flow compared to aquatic burrowing crayfishes. I speculate that in at least some species, conspicuous colors may be a neutral color trait that faces little to no selective pressure. This is one potential explanation as to why semi-terrestrial burrowing species are more likely to be conspicuously colored. Genetic studies and behavioral experiments are required to test this hypothesis.

Abstract Isopods of the genus Janiralata Menzies, 1951 (Asellota: Janiridae) are known from shallow and deep waters of the Northern Hemisphere. Most species are free-living, but some are symbiotic on the surface of other benthic invertebrates. We obtained from three beam- and four otter-trawl hauls 18 Janiralata asellote specimens from the bathyal zone off the Pacific coasts of Tohoku, northeastern Japan. Partial nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene (505 bp) were determined for 16 of the 18 collected specimens. Non-significant genetic differences (< 0.8%) indicated that the individuals were conspecifics. Morphological analysis indicated that all the specimens belonged to a single species, Janiralata planasp. nov. based on the unique morphology of the anterolateral and distolateral projections on the head and pleotelson, surface and lateral margins of the body, antennula article 1, and of the male pleopod 1. Six of the 18 collected specimens were found attached to the surface of an unidentified sea anemone (Hormathiidae), ten to the solasterid starfish Crossaster borealis Fisher, 1906 and two were obtained from the bottom sediment. Three COI haplotypes of the new species were shared by individuals from two neighboring sites, which suggests that genetic isolation occurs on a relatively narrow horizontal scale, although the bathymetric distribution range was rather wide. We describe a case study of the geographic and bathymetric distributions of an asellote species with low dispersal ability and its genetically differentiated populations. Such approach could help elucidate the diversity and distribution of deep-sea organisms and their diversification processes.

Abstract The elkhorn coral crab Domecia acanthophora inhabits shallow-water coral reefs in the Western Atlantic. The species has a wide distribution and, although primarily associated with endangered Acropora corals, has been recorded from a myriad of hosts. Here we conducted the first genomic survey and complete mitochondrial assemblage and characterisation of any species of Domeciidae, as well as the first species within Trapezioidea. The estimated size of the nuclear genome ranged from 0.64 Gbp to 1.76 Gbp, revealing a small genome. Repetitive elements of the genome were estimated here at 66.4% and 74%, respectively, with the majority of the repetitive elements consisting of LINE, LTR, and satellite DNA. The assembled A-T rich mitochondrial genome consisted of 15,568 bp in length, with 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes and two ribosomal RNA (rRNA) genes. A 619 bp long non-coding region was identified as the supposed D-loop/control region, containing eight microsatellites. The 22 tRNA genes, ranging from 65 to 71 bp in length, displayed a typical “cloverleaf” secondary structure, with the exception of tRNA-Ser1 which lacked part of the DHU arm and tRNA-Asp displayed a deletion of the TΨC loop but not the arm. Two transposition events of two tRNA genes were also found when comparing the gene order of D. acanthophora to that of the brachyuran basic gene order, which had not been reported before. Despite belonging to a widely distributed, well-known superfamily of coral-associated crabs, the Trapezioidea, very little was known about this species from a genetics perspective, which is remedied here by providing a new genomic resource for D. acanthophora.

Abstract The decapod fauna on intertidal shores in northern Chile is characterized by its relatively high diversity and abundance due to the presence of continuous upwelling by the Humboldt Current, which results in a high productivity. The decapod fauna on intertidal rocky shores is characterized by coexisting species that inhabits in natural shelters such as cracks and eroded rocks, as well as among macroalgae. We aimed to monitor the brachyuran and anomuran (porcellanid) crabs in three intertidal sites during two periods of time in September-December 2019 in the Antofagasta region, one site without human intervention and two sites in the city of Antofagasta, for which we applied null models in ecology. We assumed that the communities are random, a viewpoint that is more robust because it reduces the risk of error type I. The results of the application of null models on the co-occurrence species revealed that species associations are mainly structured for all sites, whereas the niche-sharing null model revealed that the reported species did not share ecological niches and in consequence there is not interspecific competition. The results would probably indicate that the species of intertidal decapods have a micro-specific ecological-niche differentiation, which would explain the existence of structured pattern in species associations. The results were compared with information for other sites along the continental Chilean coast.

Abstract The crustacean fossil record is dominated by mineralized forms. These fossils, in turn, are mainly decapod chelae or parts of chelae. Studies of the composition of modern crustacean cuticles have likewise been dominated by decapods. We summarize major element chemical analyses (Ca, Mg, Na, P) using SEM-EDS of modern crustacean exoskeletons from Bermuda, Georgia (USA), and Lake Tanganyika (Burundi). Although most specimens were brachyuran and anomuran crabs, material also included examples of stomatopods, isopods, caridean shrimps, and achelatans. Transects were made of sections of the carapace, palm of the propodus, and tips of either the dactyl or propodus. Multiple transects were made of the Bermudan land crab Gecarcinus lateralis. Additional studies were made of brachyuran fossil crabs from Texas and South Dakota and of brachyuran crabs having undergone ten months of burial in marine sediments. Overall, the tips of the chela were the thickest and most heavily mineralized regions and had the lowest phosphorus content. In nearly all cases, they also had the lowest ratios of Mg to Ca. One notable exception was Gecarcinus, where the denticles had elevated Mg:Ca values. Anomura and Brachyura had markedly different composition from Stomatopoda and possibly Isopoda, suggestive of independent evolutionary origins of biomineralization within the Crustacea. There were also significant differences in composition between brachyuran crabs from Georgia and Bermuda, perhaps due to differences in water temperature. The fossil crustaceans had much more phosphate in their cuticles, likely as a result of diagenetic processes. Composition should be a first order control on the fossil record of crustaceans. Future studies need to expand the taxonomic and geographic ranges of material examined, determine whether there are environmental controls on composition, and explore the relevant diagenetic processes.

Abstract Following an incidental observation of captive Clibanarius corallinus (H. Milne Edwards, 1848) supposedly removing algae from each other’s shells, we conducted a feeding experiment over 72 hours to understand its potential role as a mesograzer in coral reef ecosystems. Epiphyte-covered, coral rubble fragments of Acropora spp. were exposed to hermit crab (N = 41) activity for 72 h in a flow-through seawater aquarium system at Heron Island, southern Great Barrier Reef, Australia to understand whether hermit crabs could remove epilithic algae and if so, to what extent. Coral fragments exposed to the hermit crabs had 9.1% less chlorophyll at the end of the experiment. The detritus generated in the experimental set-up had 2.4 times more chlorophyll and 33.4% less organic biomass than the detritus generated in the control environment. The crabs did on average lose 0.11 g of their initial weight, which could have been a consequence of the experimental set-up. These results suggest that C. corallinus has the potential to contribute to the control of epilithic algae in coral reefs, with such effect having hitherto been overlooked as a result of the cryptic behaviour of this hermit crab species.