Invertebrate Biology最新文献

Sex chromosome degeneration is documented in various animal taxa and is predicted to be due, in part, to a buildup of transposable elements (TE) on the non-recombining sex chromosome (Y in mammals and W in many crustaceans). Recombination in XX (or ZZ) individuals is predicted to reduce the buildup of TEs on the X (Z), but because there are no YY (WW) individuals, such TE buildup goes unchecked on the Y or W. Herein, we report an analysis of TEs in the genome of a crustacean that has both ZZ and WW individuals. The purported W chromosome did show linkage with several known sex-linked loci. However, the prediction of a buildup of TEs throughout the purported W was not found: neither the predicted accumulation of the TE types LINE and LTR nor the expected higher TE numbers were observed on the purported W. We could not exclude the possibility of TE buildup in a smaller non-recombining region of the W chromosome, which is predicted in species in the earliest stages of sex chromosome development. These results allow a glimpse into the earliest stages of sex chromosome evolution in these branchiopod crustaceans.

To understand the seasonality of spermatogenesis in cultured males of Mytilus edulis from a cold-ocean environment, we investigated the cellular transitions occurring within the spermatogenic epithelium of the testicular acini during early and advancing spermatogenesis, with specific reference to the histology of the epithelium, gene specific spermatogenic response, condition, culture environment, and season. A combination of histological evaluation, qPCR analysis, and in situ hybridization was used to examine the cellular transitions taking place in the germinal epithelium from late winter through to a seasonal spawn in summer. We observed clear seasonal transitionary changes in the spermatogenic cell population making up the germinal epithelium (i.e., spermatogonial stem cells, spermatocytes, spermatids, and spermatozoa) extending from February to July. These seasonal transitions in spermatogenic cell type coincided with significant variation in the spatiotemporal expression of two molecular markers for spermatogenesis (i.e., Kelch-like protein 10 [KLHL10] and Armadillo repeat-containing protein 4 isoform X2 [ARMC4]) but not for expression of a gamete-specific Mitochondrial cytochrome oxidase I (MT-COI). The spatiotemporal expression of these genes is directly linked to the cellular changes taking place in the germinal epithelium during spermatogenesis. These observations not only corresponded to seasonal changes in physiological condition but also environmental temperature and chlorophyll a, thus further supporting the link between male gametogenesis and environment in higher latitude regions.

Road salt (NaCl) is the most common deicer used to melt snow and ice from roadways in cold climates, but its use results in runoff of sodium and chloride ions into sewers and into soil and freshwater ecosystems. Road salt causes harmful effects on wetland habitats, which host an abundance of macroinvertebrate species. Alternatives to road salt, such as beet juice, are commercially available, but their impact on invertebrates is less well studied. We examined the impact of road salt alternatives on four invertebrate species (Daphnia pulex, Eisenia fetida, Heterocypris sp., and Culicoides sp. larvae), some of which come from a naturally brackish area. Our expectation was that road salt alternatives (beet salt, molasses, pickle juice, and sand) would be less toxic to the animals than traditional road salt. This study comprised two experiments: the first exposed individuals of the four invertebrate species to road salt alternatives, and the second exposed the invertebrates to a range of road salt concentrations. Only individuals of D. pulex were negatively impacted by road salt. The other invertebrates were not significantly affected by any salt alternative, demonstrating interspecific differences in response to salt. Species found in naturally salty environments were more tolerant of both road salt and alternatives. This research shows species- and habitat-specific responses to road salt alternatives, which has implications for municipalities looking to salt roads without negatively impacting freshwater ecosystems.

The musculature of parasitic flatworms plays a central role in locomotory movement, attachment to the host, and in the function of the digestive, reproductive, and excretory systems. We examine for the first time the muscle system of the flatworm Dicrocoelium dendriticum, a causative agent of the parasitic disease dicrocoeliosis, by use of fluorescently labeled phalloidin and confocal laser scanning microscopy. Somatic musculature of D. dendriticum consists of the circular, longitudinal, and diagonal muscles. The distribution of the muscle fibers in the body wall differed among the anterior, middle, and posterior body regions of the worm. The musculature of the attachment organs, the oral and ventral suckers, includes several types of muscles: the external equatorial and meridional muscles, internal circular and semicircular muscles, and radial muscles. Inside of the ventral sucker the diagonally located muscles were revealed and the supplementary u-shaped muscles were found adjoined to the base of the sucker from outside. The musculature of the internal organs composed of the excretory, reproductive, and digestive systems were characterized. Our results increase our knowledge of the morphology of trematodes and the arrangement of their muscle system.

Echinoderm skeletons are composed of calcium carbonate ossicles that join in a variety of ways to form flexible or, more rarely, fixed joints. Ossicle “fusion” in echinoderms has been widely reported in the literature to form various types of fixed joint, but fusion in the sense of chemical union (ankylosis) of the calcitic ossicles has rarely been demonstrated. The arm skeleton of ophiuroids is primarily composed of a series of vertebral ossicles; each vertebra is a compound ossicle that consists of paired ambulacral ossicles united by a fixed joint, often reported to be fused. Development of vertebral ossicles in the amphiurid brittlestar Ophiophragmus filograneus from the arm tip to the oral frame was examined using scanning electron microscopy to follow ontogeny of the vertebra. As an ambulacral ossicle grew, its stereomal trabeculae interdigitated and interlocked by hooking around those of its paired ambulacral, forming the characteristic sinuous suture line central to ophiuroid vertebrae. This three-dimensional interlocking of stereom formed the joint between paired ambulacrals. With further growth of the vertebra, limited fusion of trabeculae of the paired ambulacrals added to the structure of the joint, primarily at the articular surfaces between successive vertebrae. The joint found here with interlocked trabeculae between ambulacral ossicles of O. filograneus appears to be the same type described in the literature in some echinoids and other ophiuroids. This unique type of fixed joint is described here and named the “campylogomphosis” (Greek: campylos, bent; gomphos, bolt). This newly recognized joint might have implications in echinoderm phylogeny, comparative biology, medicine, and materials science.

Olivancillaria carcellesi occurs in shallow sandy shores from north Patagonia, in intertidal and subtidal sandy bottoms. Females of O. carcellesi exhibited a remarkable specificity for spawning on the shells of living males and females, indiscriminately, of the buccinanopsid Buccinastrum deforme, measuring 26.9 ± 4.7 mm in shell length. The egg capsule was semispherical and attached to B. deforme shells by a small elliptical and wide base. The capsule was translucid when spawned, with a thick and semirigid wall and a hatching aperture of 1.8 ± 0.1 mm (n = 111) in diameter. Each egg capsule contained a single egg that measured 1367 ± 34 μm (n = 5) in diameter before cleavage. The embryo developed a small bilobed velum and an operculum, which were both lost before hatching as a crawling juvenile of 1762 ± 47 μm (n = 28) in shell length. As in other species in the genus, the eggs of O. carcellesi are among the largest in the caenogastropods with direct development. The time from oviposition to hatching is estimated to be approximately 6 months.

The eastern oyster (Crassostrea virginica) is a protandrous hermaphrodite of commercial importance. As with many marine invertebrates, little is known about sex determination and differentiation systems in this species. Such knowledge has important implications not only for understanding the evolution of sex but also for applied questions in aquaculture. In order to examine mechanistic differences in reproductive development between the sexes, we compared the transcriptomes of gonad and mantle tissues from six male and six female oysters. A total of 7675 transcripts were differentially expressed between male and female gonads (3936 and 3739 were upregulated in males and females, respectively). Transcripts identified include those associated with sex in other invertebrate and vertebrate species such as Dmrt1, Sox-30, Bindin, Dpy-30, and Histone H4 in males and Foxl2, Vitellogenin, and Bystin in females. GO terms associated with transcripts upregulated in male gonads include protein modification, reproductive process, and cell projection organization, whereas RNA metabolic process and amino acid metabolic process were associated with transcripts upregulated in females. Far fewer transcripts were differentially expressed between male and female mantle tissues, with 87 transcripts upregulated in females and 16 upregulated in males. However, 41% of transcripts identified as differentially expressed between mantle tissues were also differentially expressed between male and female gonads including Histone H4 and Bystin. This study represents the first characterization of eastern oyster male and female gonad transcriptomes. We further identify differing expression profiles between male and female mantle tissues, which provides evidence for sex-specific functions of the mantle and suggests that this tissue could harbor biomarkers for identifying oyster sex non-destructively.

Dicyemids (Phylum Dicyemida) are the most common and characteristic endosymbiont living in the renal sac of benthic cephalopod molluscs. Precocious development of a hermaphroditic gonad occurs in the larvae and smaller juveniles of 40 dicyemid species from 17 cephalopod species so far and is the usual phenomenon in dicyemids. Based on the developmental and morphological features of precocious individuals, progenesis (a form of heterochrony) is the appropriate term for such precocious development. In general, progenetic individuals have much lower fecundity than normal ones because of their smaller body size, and therefore, it appears to be a disadvantageous reproductive trait. Nonetheless, the number of progenetic individuals consists of 30%–50% of the population, a relatively large proportion suggesting that the presence of progenetic individuals probably plays an important role in life history strategy. Precocious development significantly reduces growth time and enables early maturation. Progenetic individuals are common in short-living cephalopod species, in which precocious development seems appropriate for dicyemids, enabling fast larval release before the end of the host's life span.

The vast majority of species interactions in nature go unnoticed because they occur under circumstances unamenable to observation. This is unfortunate, as our understanding of trophic ecology is predicated on our ability to quantify the nature and magnitude of species interactions. Here, we use specimens from museums and private collections to estimate prey breadth and morphological patterns between predator and prey pairs of the malacophagous Cychrini beetles collected alongside their snail prey. We identified each pair, measured a series of morphological traits on each, and tested for relationships between the morphological characteristics of beetles and the snails they were found eating. Of 38 specimen pairs, we identified 12 species of Cychrini beetles from two genera (Scaphinotus and Cychrus) eating 22 species of snail prey from 12 genera and ranging from 1 to 9 species of snail prey per beetle species. We found 29 unique predator–prey species pairs. Irrespective of species identity, we found that female beetles were discovered eating larger snails compared to male beetles. We detected two trends in which larger beetles were found eating snails with relatively larger aperture openings, and beetles with more slender body shapes (longer, thinner mandibles, heads, and pronota) were found eating snails whose shells had relatively smaller aperture openings. This suggests that, even within the carabid tribe Cychrini, variation in the cychrine body form may influence prey availability. This study provides the most comprehensive list to date of predator–prey pairs in this understudied group of beetles and also demonstrates the utility of museum collections for documenting cryptic species interactions.

Gastropod molluscs, which serve as obligatory intermediate hosts for digenetic trematodes, possess an internal defense system (IDS) consisting of phagocytic hemocytes and plasma factors. This IDS is responsible for resistance to infection with larval trematodes, which are encapsulated and killed by hemocytes in incompatible snails. Like other physiological systems, the IDS probably undergoes maturation during early stages of life, and the relatively undeveloped state of the IDS in young snails has been hypothesized to be a factor in their increased susceptibility to infection with larval trematodes. In this study, hemocytes were examined in the BS-90 laboratory strain of Biomphalaria glabrata that is resistant to infection with Schistosoma mansoni as adults but susceptible to infection as neonates. Compared with hemocytes from adults, hemocytes from neonates had a smaller perimeter and lower intrinsic directional motility on glass microscope slides. Additionally, in vitro assays showed a lower association with fucoidan-linked polystyrene beads and less ability to produce superoxide anion in hemocytes from neonates compared to hemocytes from adults. These results support the hypothesis that the gastropod IDS undergoes maturation during growth. However, whether the observed differences between hemocytes of neonatal and adult BS-90 snails play a role in the susceptibility of the former and resistance of the latter to infection with S. mansoni is not known.