Invertebrate Biology最新文献

The reproductive biology of the branching octocoral Antillogorgia americana was studied at a site on the Caribbean coast of Panama in 1990–1991 by examining the reproductive status of 11 colonies across 14 months. Colonies were gonochoric. The presence of large and mature eggs or spermaries was allochronic across colonies and months, with peak gonad volumes occurring in months ranging from October through May. Reproductive effort varied between branches on a colony, with variation between branches and branchlets accounting for 25% of the random variation between polyps. Branchlets at the tip of the colony had fewer mature eggs than those lower on the branch, and polyps at the tips of the branchlets had fewer still. Although the simultaneous release of eggs and sperm is critical to reproductive success, the lack of synchrony among colonies on the scale of months may reflect less need for all colonies to spawn in a single event among abundant species that release large numbers of gametes. Such a strategy also spreads the risk of reproductive failure due to environmental conditions during any single month. The presence of multiple spawning episodes can also drive the reproductive isolation of populations and may reflect the presence of cryptic species within the taxon. Studies of reproductive timing can be an important adjunct in identifying variation in life history strategies as well as assessing the validity of species boundaries.

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.