Invertebrate Biology最新文献

Coelomocytes in the Holothuroidea are traditionally identified according to their morphology through light, fluorescence, or electron microscopy. Former studies have typically used only one method, with few works combining two or more approaches. Studies using cytocentrifugation to study these cells are scarcer. Thus, for the first time, an integrative approach was used to compare coelomocytes in Holothuroidea. This approach consisted of living and stained cells, scanning electron microscopy (for spherule cells), and accurate morphometric analyses. Specifically, we used specimens of Holothuria grisea, Holothuria arenicola, and Holothuria tubulosa to test whether cytocentrifugation could be valuable in comparative studies with coelomocytes, whether an integrative approach could help to understand spherule cell diversity, and whether closely related species, even those having distinct geographic distributions and ecological requirements, would have a similar population of coelomocytes. Our results showed seven distinct cell types in these species, including phagocytes, fusiform cells, morula cells, acidophilic spherulocytes, spherulocytes, progenitor cells, and crystal cells. Total and differential cell counts, along with morphometric parameters, were similar among species. Morphometric analyses of spherule cells revealed consistent differences among the diameter of their cytoplasmic spherules, as well as a set of different morphotypes in acidophilic spherulocytes and spherulocytes. Cytospin preparations proved to be quite useful because they provided constant morphological and morphometric data, allowing accurate identification of the cell types and comparisons among species. Moreover, this study highlighted (1) that the spherule diameter is a good parameter to separate spherule cells and (2) a putative maturation process to acidophilic spherulocytes and spherulocytes. Lastly, we showed that the cells of these species are very similar, regardless of their geographic distribution and ecology. Thus, our work contributes to a better understanding of the coelomocytes in Holothuria, a genus with a wide geographic distribution. The present study may be useful to establish these species as important model organisms, as well as bring insights into the functions of coelomocytes.

Cephalopoda have no true larval stage because they lack any abrupt morphological changes during growth. However, in shallow-water merobenthic octopuses, changes occur in the relative proportions of their body parts during the planktonic paralarval phase and the transitional phase from plankton to benthos. How this lifestyle transition is achieved is unclear because the morphological changes during their early life have yet to be fully elucidated. To address this issue, using laboratory-raised East Asian common octopus, Octopus sinensis, aged 0–100 days after hatching, measurements were taken of total length (TL), mantle length (ML), arm length (AL), the number of suckers on an arm (ASC), and body dry weight (DW). These values were used to explore break points (BPs) in the log-transformed allometric growth equation: lny = lna + blnx, where x is TL (a reference body dimension) and y is one of the other measurements. In all measurements, a three-segmented allometric growth model with two BPs was statistically evident, and each segment had a different relative growth coefficient b along with growth, indicating that there are distinct stages of ontogenetic morphological change. Taking into account the times of behavioral changes reported so far, four stepwise phases were detected in the progress of O. sinensis towards settlement: (1) a true planktonic paralarval phase with rapid increase of ASC; (2) a transitional phase between plankton and benthos, characterized by rapid AL increase; (3) a provisional initial benthic juvenile phase, attaining longer AL than ML and approaching adult-like proportion; and (4) a true benthic juvenile phase, reaching almost completion of the change in body proportion. The stepwise morphological changes seem to be a compromise measure to achieve changes in functional morphology and behavior necessary to lifestyle transition from plankton to benthos for an organism that goes through morphological change without metamorphosis.

The giant keyhole limpet, Megathura crenulata, lives in rocky intertidal and subtidal environments along the Southern California coast, where it is exposed to viruses, bacteria, and other potential pathogens. We demonstrate that when exposed to bacteria or latex beads, hemocytes from specimens of M. crenulata in vivo and in vitro immediately become adhesive and form nodules. The rapid activation of hemocytes suggests a role for an array of recognition proteins, and inhibition of nodulation by the tripeptide Arg–Gly–Asp indicates that integrins are involved. The morphological changes involved with nodule formation include the rapid extension of lamellipodia, phagocytosis of particles, and compaction of the hemocyte aggregates. The number of nonadherent hemocytes rapidly decreases as aggregates form. The elimination of bacteria is due to a dynamic hemocyte response, rather than antibacterial factors in the plasma. These findings are compared to work on other gastropods and expand the current knowledge on the immune response of molluscs, such as M. crenulata, which is increasing in importance as they continue to be raised in aquaculture for pharmacological use.

Understanding how water limitation affects the performance of herbivorous insects is relevant in a context of worldwide alterations of rainfall regimes due to climate change. Apart from its influence on insect growth and development, water availability has also been considered a cue for color polyphenism in some species. This is the case of the grassland-inhabiting admirable grasshopper (Syrbula admirabilis), for which water content in plant tissues, a potentially reliable cue to predict future vegetation conditions, has been proposed to determine the frequency of green–brown color morphs. We performed an experiment that manipulated water content of the diet (dry/wet treatment) in a group of individually monitored admirable grasshoppers to explore the effects on imago size, timing of female first mating, and coloration. Our results showed that grasshoppers in the wet treatment achieved larger sizes, and females mated comparatively earlier, than their counterparts in the dry treatment. We also found that hue (the dominant color) in imagines was significantly lower (browner) than in nymphs, but the magnitude of this color shift did not differ between treatments. This study supports the idea that water limitation has a negative impact on grasshopper growth and development, but rules out dietary water content as a cue for color polyphenism. This result encourages additional research to assess the actual contribution of environmental and genetic factors to color determination in admirable grasshoppers. Such information could help to better understand how color polymorphism is maintained in natural populations and to predict how it could evolve in a future in which environmental conditions will become more unpredictable.

The annelid clade Amphinomidae, commonly known as “fireworms,” is notorious for causing skin inflammations after physical contact. These injuries are caused by the chaetae of the animals, which are calcified and particularly brittle. The incorporation of calcium carbonate particles and their disintegration cause the chitinous lamellae within a chaeta to break apart and result in a prominent inner cavity. Although the chaetae of Amphinomidae are well studied, data concerning their sister group, Euphrosinidae, are scarce. In this study, we examined the chaetae of two species of Euphrosine for the first time regarding the variety of chaetal types, their ultrastructure, elemental composition, and arrangement. This allows us to get a better understanding of chaetal characteristics in the ground pattern of Amphinomida. We were able to determine bifurcate chaetae as the primary chaetal type in Amphinomida and provide evidence that their aciculae must have evolved secondarily. Calcification is a common feature among amphinomidan chaetae and regarded as autapomorphy of Amphinomida. Finally, a single dorsal formative site in each notopodium and neuropodium, found in Euphrosine foliosa, likely represents the ancestral state in Amphinomida. There is no evidence for venom production or secretory cells associated with the chaetae of Euphrosine, which is in accordance with what was previously observed in Amphinomidae. Our study also complements further studies into chaetal characteristics such as the number and arrangement of formative sites.

Suspension-feeding bivalves are critical members of aquatic ecosystems worldwide, which is why research into their host-associated microbiota is growing. Experiments that artificially diminish the native microbial communities of bivalves in vivo will be increasingly necessary to evaluate the functional role of microbes within their hosts. Previous methods to manipulate the microbiome of bivalves lack standardization and, often, verification of successful disturbance. The goal of this study was to evaluate antibiotic administration as a method for perturbing the gut microbiome of bivalves in two separate, but related, experiments. In the first, a mixture of antibiotics was delivered to eastern oysters for 4 days to probe effects on gut microbial carbon usage, diversity, and taxonomic composition. In the second, the same antibiotic mixture was administered to blue mussels for 21 days to probe effects on microbial abundance, diversity, and taxonomic composition. In both experiments, animals were administered antibiotics in isolation, and stringent sterilization methods were employed, which included sterilized seawater and microalgal food. The results of the oyster experiment revealed that antibiotics substantially reduced microbial carbon usage and perturbed community composition. In the mussel experiment, antibiotics lowered microbial abundance and species richness and significantly altered community composition. Taken together, results from the two experiments demonstrate that antibiotics can be used to effectively alter the function and composition of the gut microbial community of bivalves. Future research that aims to perturb the microbiomes of suspension-feeding animals should incorporate aspects similar to the protocols described herein. Additionally, future studies must include verification, ideally high-throughput DNA sequencing coupled with microbial quantification, that the antibiotic perturbation was successful.

Little is known about reproduction of the sea pen Pennatula aculeata, which is found at high densities and constitutes vulnerable habitat in the Gulf of St. Lawrence, Canada. Sex ratio, size at maturity, and reproductive status were investigated for colonies collected in May, August, and October 2015 along the Gaspé Peninsula. Reproductive status was assessed by histological determination of gamete sex and maturity and by stereomicroscope measurement of the diameters of the leading cohort of oocytes (LCO) or sperm cysts of histologically mature colonies. Colonies were gonochoric, with a sex ratio of 1:1. Based on the distribution of gamete diameters in May, three groups of female and a single group of male colonies were identified. Female colonies classified in the group of LCO with the smallest diameter (0.10–0.39 mm) were shorter in total length (TL < 130 mm) than females in the other two groups of LCOs with larger diameters, and very few spawned from May to October. A major reduction in the proportion of large female colonies (TL ≥ 130 mm) belonging to the group with the largest diameter (≥0.55 mm) and of mature male colonies between May and August indicated one annual spawning event. Persistence of histologically mature (vitellogenic) female colonies classified in the two smaller oocyte diameter groups after spawning is indicative of prolonged oogenesis (at least 24 months). The fact that only approximately half of the large female colonies had ripe oocytes (diameter ≥0.55 mm) in May prior to spawning, while the other half had vitellogenic oocytes of much smaller diameter which persisted after the spawning period, suggests that they reproduce only every other year. Estimated size and age at which 50% of colonies spawned were greater in females (148 mm TL, 11–14 years) than in males (101 mm TL, 8–11 years). These reproductive characteristics may reduce resilience of P. aculeata to various anthropic stressors.

Caudofoveata is a clade of worm-like mollusks that lead a burrowing lifestyle in soft marine sediments. There are only a few references to peristaltic movement in members of Caudofoveata. The movement of individuals of Chaetoderma nitidulum collected from the White Sea and set into a transparent gelatin substrate was described by direct observation. The morphology and ultrastructure of the musculature and circulatory system were described in detail using morphological methods (light and electron microscopy, and 3D reconstruction from a series of semithin sections). Based on the analysis of the movement and morphology of the body wall and body cavities, the main phases of movement were distinguished. The peristaltic movement observed in C. nitidulum is superficially similar to the peristalsis phases described for Annelida and completely coincides with the classical description of direct peristalsis.

This study explores the potential use of photos for extracting basic data on spider eggs and presents a first rough but comprehensive overview of egg sizes, egg numbers per egg sac, and egg sac shapes in 468 species of pholcid spiders representing 73 genera. Egg diameters ranged 0.29–1.73 mm; egg numbers ranged 3–110. Egg sacs were mostly round or oval, but tended to be elongated in species with elongated abdomens, and flattened in very short-legged species. Potential effects of female body size, abdomen shape, and microhabitat on egg size and number were evaluated by phylogenetic generalized linear models across all investigated species. Our analyses showed that both egg size and egg number are strongly determined by female body size. We found a clear trend for small species to have relatively larger eggs. Ecology and body shape also played a role, albeit at a considerably lower level and with complex interactions among variables: Relative to body size, ground-dwelling species had smaller eggs than space and leaf dwellers; species with a long abdomen had larger eggs than species with a short abdomen. The effect of body size on clutch size depended on body shape and microhabitat: It was slightly weaker in space-dwelling than in other species; species with long abdomens had more eggs in ground and leaf microhabitats, whereas space dwellers carried more eggs when having short abdomens.

South Africa harbors a rich and diverse terrestrial snail fauna. Despite their importance in ecosystem functioning and structure, their alpha taxonomic diversity is poorly understood, and most groups have not been the subject of molecular systematic scrutiny. During the present study, we used the mitochondrial cytochrome c oxidase subunit I (COI) locus to start a DNA barcode reference library, to examine intra- and interspecific genetic divergence, and to explore the presence of cryptic diversity among terrestrial gastropods from forested regions in the country. We generated 399 COI barcodes comprising 70 morphospecies in 26 genera and 15 families, representing nearly 10% of the described gastropod diversity in South Africa. Our results showed a substantial overlap between mean intraspecific and interspecific genetic variation and no barcoding gap. Three species delimitation methods—Poisson Tree Processes (PTP), Refined Single Linkage (RESL) algorithm in Barcode of Life Data Systems, and the Automatic Barcode Gap Discovery (ABGD)—applied to selected widespread species retrieved incongruent operational taxonomic units (OTUs). These results, coupled with high intraspecific variation, suggested cryptic diversity among several terrestrial gastropod genera in the country. We further demonstrated that DNA barcoding analysis holds the potential for highlighting cryptic lineages in snails and for revealing taxa in need of taxonomic revision. We recommend that future taxonomic studies of South African terrestrial snails incorporate multiple sources of information for species delimitation.