Invertebrate Biology最新文献

Mechanical properties of the skeleton of four antipatharians (the whip species Cirrhipathes anguina and Stichopathes cf. maldivensis, and the branched species Cupressopathes abies and Cupressopathes cf. pumila) living in shallow waters off the southwestern coast of Madagascar were investigated using a three-point bending test. The Young's modulus did not differ according to species but was significantly higher in the distal segment of colonies, compared with the basal and median segments. By contrast, the flexural stiffness was significantly higher in whip species compared with branched ones, and in the whip species, flexural stiffness was higher in the basal segment compared with the other two segments, an observation consistent with a specific adaptation of the species to a strong current environment. Although both species cohabit identical flow conditions, whip species are able to maintain their stalk in vertical position, whereas branched species can readily bend over. This suggests that the specific flexural stiffness is linked to contrasting feeding strategies of species with different morphologies in a similar strong current environment.

Ophiopholis aculeata is a ubiquitous brittle star (Echinodermata: Ophiuroidea) known to occur from the upper subtidal to the bathyal zone. Individuals from shallow inshore habitats (rhodolith beds and rock fields) and deeper offshore locations in eastern Canada were studied to assess the population structure, habitat selection, diet, and feeding strategies of this species through use of stable isotope analyses, gut contents, and laboratory experiments. Potential drivers of habitat selection such as depth, light conditions, body size, sex, intraspecific competition, and presence of predators were examined. This study highlighted variable population size structures and abundances as well as diversified food sources and feeding strategies (i.e., suspension and deposit feeding, scavenging, predation on live organisms, and even cannibalism) as a function of native depth and habitat. It also revealed that studies on the feeding biology of brittle stars must carefully consider sex and life stage as driving factors.

Intertidal zones are highly dynamic environments. At low tide, temperatures and salinities in intertidal tide pools can change substantially and quickly, depending on the weather conditions on a given day and the volume of water in the pools. As we begin to feel the effects of climate change more strongly, conditions in tide pools will likely become even more extreme. The long-wristed hermit crab Pagurus longicarpus can be found intertidally and subtidally along the Atlantic coast of North America from Nova Scotia to Florida, as well as along the Gulf coast. At low tide, they can often be found in tide pools. We tested the effects of temperature, salinity and their combination on the ability of hermit crabs to select high-quality shells of appropriate size over relatively small shells and shells that had been drilled by predatory snails. Exposing hermit crabs to a temperature of 33°C and a salinity of 40 ppt after a gradual increase from 21°C and 30 ppt had the greatest effect on the quality of shells occupied by the hermit crabs over the next 24 h, compared with shells occupied by hermit crabs that remained at the control temperature and salinity of 21°C and 30 ppt. Changing the temperature and salinity to 30°C and 40 ppt also had a noticeable effect on shell choice, as did increasing the temperature alone to 33°C. Our results suggest that as the planet warms and precipitation patterns change, intertidal hermit crabs of the species P. longicarpus will likely more often be found occupying shells that are damaged or not of an appropriate size, leaving the hermit crabs more exposed to predation, desiccation and other stressors.

Infestations of commercially cultured eastern oysters (Crassostrea virginica) by shell-boring spionid polychaetes are common in the northeastern United States. Historically, infestations were attributed to Polydora websteri, also known as mud-blister worm. Among samples of shell-boring worms sampled from eight oyster farms in northern New England (Maine, New Hampshire, and Massachusetts), we detected P. websteri, as well as worms that were morphologically distinct from P. websteri. Using a combination of light and scanning electron microscopy, along with analysis of molecular variation at the nuclear 18S rRNA and mitochondrial cytochrome c oxidase I (COI) genes, we determined that specimens related to two other species of Polydora, Polydora onagawaensis and Polydora cornuta, were inhabiting burrows within the shells of oysters. Polydora cornuta is not recognized as a shell-boring species and likely invades existing burrows opportunistically. Our analysis of COI sequences identified three distinct genetic lineages among specimens morphologically identified as P. cornuta; one of these lineages is much more geographically widespread than previously had been reported. Polydora onagawaensis is considered a shell-boring species, and our article constitutes the first time this species has been documented in the Northwest Atlantic. We also provide evidence for three divergent COI genetic lineages that occur sympatrically among the specimens provisionally identified as P. onagawaensis in the northeastern United States.

Intertidal zonation of organisms is well studied on rocky shores but less so in soft sediment communities. On rocky shores, communities are two dimensional, with biotic factors such as competition and predation setting the lower bound of a zone, whereas abiotic factors such as desiccation set the upper bound. In soft sediment communities, these patterns persist, but with a dynamic three-dimensional ecosystem occupied by mobile infaunal organisms, zonation can be more difficult to quantify and detect. Hemichordate worms, however, deposit fecal casts at the surface, which can be easily identified and counted, making them a potential model system for identifying zonation in soft-sediment systems. Here, we describe the intertidal zonation of hemichordate worms at two sites in Maine and Virginia. In Virginia, Saccoglossus kowalevskii occurs in the mid-intertidal at densities up to 500 individuals per square meter, whereas a tube-building polychaete, Spiochaetopterus oculatus, dominates the lower intertidal. In Maine, two hemichordate species, Saccoglossus bromophenolosus and Protoglossus graveolens, co-occur at densities up to 100 individuals per square meter in the mid-intertidal, whereas hermit crabs and errant polychaetes are numerically dominant in the low intertidal. Despite known chemical defenses, crustaceans readily consumed hemichordates in lab assays, although polychaetes did not. In a field tethering experiment, loss rates of hemichordate-flavored agarose pellets increased as tidal height decreased, suggesting that the lower bound of the hemichordate zone could be set by biotic forces such as crustacean predation. Additionally, a field transplant experiment found low survivorship of hemichordates transplanted to the upper intertidal, suggesting that desiccation may set their upper bound. These results are broadly consistent with prior studies of zonation in soft sediments, and expand our limited understanding of basic hemichordate ecology.

The spider crab Maiopsis panamensis is the largest brachyuran crab in the Gulf of California and is found mainly in deep water. This study of the spider crab reproductive cycle in Mexican coastal waters used histological and chemical methods to describe oogenesis in detail and to define a scale of maturity based on visible characteristics for the different stages of gonial cells. The criteria used in the description of oogenesis were oocyte diameter, nucleus morphology, ooplasm characteristics, and degree of yolk accumulation, as well as lipid, protein, and carbohydrate content. These results showed that maturation and spawning are continuous in this species during most of the year, with small variations in the proportion of ovigerous females. The lowest frequency of mature females was found in spring (March to May) and summer (June to August). The organisms migrate to greater depths in the second half of the year. Maiopsis panamensis was found to have high reproductive potential because each female can produce multiple generations of oocytes in the ovaries while carrying the ovigerous mass. These characteristics mean that females spawn and hatch larvae numerous times throughout the year. Studies on the biology of this spider crab combined with study of techniques for catching them would allow informative strategies towards the sustainable use of this species in the Mexican Pacific Ocean and the Gulf of California.

Sponges are a diverse phylum of sessile filter-feeding invertebrates that are abundant on Caribbean reefs and provide essential ecological services, including nutrient cycling, reef stabilization, habitat, and food for a variety of fishes and invertebrates. As prominent members of the benthic community, and thus potential food resources, factors determining the biochemical and energetic content of sponges will affect their trophic contributions to coral reef ecosystems. In order to evaluate the influence of geographic variation on biochemical composition and energetic content in the tissue of sponges, we collected several common and widespread species (Agelas conifera, Agelas tubulata, Amphimedon compressa, Aplysina cauliformis, Niphates amorpha, Niphates erecta, and Xestospongia muta) from multiple shallow reefs in four countries across the Caribbean Basin, including Belize, Curaçao, Grand Cayman, and St. Croix, U.S. Virgin Islands. In addition, we correlated inherent species-level traits, including the production of antipredator chemical defenses and the relative abundance of microbial symbionts, with biochemical and energetic content. We found that energetic content was higher in sponges with antipredator chemical defenses, and was significantly correlated with the concentration of chemical extracts from these sponges. We also noted that sponges with high microbial abundance contained significantly more soluble protein than sponges with low microbial abundance. Finally, both biochemical and energetic content varied significantly among sponges from different locations; sponges from Grand Cayman had the highest lipid and energetic content, whereas sponges from Belize had the highest carbohydrate content but lowest energetic content. Despite similar environmental conditions at these sites, our results demonstrate that biochemical and energetic content of sponges exhibits geographic variability, with potential implications for the trophic ecology of sponges throughout the Caribbean Basin.

Among the least studied clade of velvet worms (Onychophora) is a clade of Neotropical Peripatidae (=Neopatida). Neopatida has been traditionally divided into an Andicoles group and a Caraïbes group, which now correspond to Oroperipatus and the remaining genera, respectively. Panama is located in a unique position bridging the faunas of both clades and of two large continents, both of which host an important diversity of velvet worms, yet taxonomic study of the Panamanian onychophorans has been largely neglected. In this study we critically evaluate the onychophoran diversity of Panama, redescribe a species from the former Canal Zone and describe a new species from the Pacific side, close to Costa Rica, as Epiperipatus bernali sp. nov., with a unique combination of characters visible under the SEM. We further discuss the existence of multiple lineages of Onychophora in Panama, both from the Andicoles and Caraïbes groups, and within the latter, with connections to different lineages, both from South and Central America.

Poliometra prolixa is a common species of comatulid crinoid in the Arctic deep sea. In this study, we characterize the ontogenetic development through the cystidean and pentacrinoid stages, using specimens from the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the Fram Strait, Arctic Ocean. While embryos and early larval stages (e.g., the doliolaria) were not observed, both post-settlement stages and adults of P. prolixa were observed on the same moored experimental platform at 2,500 m water depth, suggesting that larvae of P. prolixa do not disperse far from their mothers. This indicates that doliolariae may have an abbreviated pelagic duration period or may be brooded in this species. The cystidean has a short, translucent stalk with a star-shaped attachment disc and a diamond-shaped translucent head. Metamorphosis from the cystidean to the pentacrinoid is characterized by the formation of brachial ossicles from oral ossicles and by fusion of the basal and radial ossicles to form the calyx. The pentacrinoid stalk is opaque and first develops synarthrial joints at the distal end. Late pentacrinoids have a xenomorphic stalk, bifurcated arms with pinnules, and cirri. We discuss the reproductive and ecological niche of P. prolixa and also consider the question of whether cystidean and pentacrinoid stages undergo metamorphosis.

Despite their important ecological roles in marine ecosystems, reproduction and early life stages of the majority of marine sponges remain undescribed. Here we characterize the mode of reproduction and the early life stages of an abundant sponge in temperate Pacific waters, Crella incrustans. Through histology, we characterized the production of gametes and the sequential steps of larval ontogeny. Using in vivo observations, we described larval release, settlement, and metamorphosis. Specimens of C. incrustans presented spermatocytes, oocytes, and several developmental stages in the sponge mesohyl during the Australasian summer (from January to March 2020), demonstrating this sponge to be a simultaneous hermaphrodite with internal fertilization, asynchronous development, and brooded embryos. As in other viviparous demosponges, mature embryos were released during the Australasian summer as free-swimming non-tufted parenchymella larvae. Under laboratory conditions, 94.3% of larvae settled within 2 days and metamorphosed into functional settlers within a week. Gametogenesis, embryonic development, larval characteristics, settlement, and metamorphosis of C. incrustans are consistent with the reproductive features common to the majority of poecilosclerid sponges. Overall, our study provides important information on the early life stages of this temperate model species for future ecophysiological experiments.