Zoology最新文献

Birds living at high latitudes perceive the photoperiod through deep-brain photoreceptors (DBP) located in deep-brain neurons. During long photoperiods the information transmitted by these photoreceptors increases the activity of the hypothalamic-pituitary-gonadal (HPG) axis, leading to gonadal development. The presence of photopigments such as VA-Opsin, Opn4, Opn5 and Opn2 in brain areas implicated in reproductive behaviors has been firmly established in several avian species with seasonal breeding, whereas their existence in opportunistic breeding birds remains unconfirmed. The Eared Dove is an urban and peri-urban dove that breeds throughout the year. Males of this species do not exhibit the typical gonadal regression/recrudescence cycle, thus posing the question of what occurs upstream of the HPG axis. We addressed this issue by first studying the presence of diverse opsins located in DBP in the brains of Eared Dove males and whether these photopigments changed their expression throughout the year. We carried out an immunohistochemistry analysis on three different opsins: Opn2 (rhodopsin), Opn3 and Opn5. Our results demonstrate the discrete neuroanatomical distribution of these opsins in the brain of Eared Dove males and strongly indicate different seasonal expressions. In the anterior region of the hypothalamus, Opn2-positive cells were detected throughout the year. By contrast, Opn5 was found to be strongly and seasonally expressed during winter in the anterior and the hypothalamic region. Opn3 was also found to be significantly and seasonally expressed during winter in the hypothalamic region. We thus demonstrate for the first time that males of the Eared Dove, have three different deep-brain opsin-expressing photoreceptors with differential location/distribution in the anterior and hypothalamic region and differential seasonality. The persistence of Opn2 and the strong seasonal expression of nonvisual photopigments Opn3 and Opn5 in two areas of the avian brain, which are associated with reproduction, could be the primary distinction between seasonal and opportunistic breeders.

Otoliths are small calcium carbonate structures found in the inner ear of fish and they, as one of important information carriers, are applied in diverse ecological fields. Otoliths are usually photographed and used to explore many unsolved biological and ecological questions. However, many anomalies may occur in the large volume of otolith image data due to natural or artificial consequences, which brings a huge bias to the aimed study and even misleading results. In this study, we first propose a specific definition of otolith anomalies and provide a dataset of otolith anomalies with Electrona carlsbergi, one of the most abundant species of lanternfishes, as the study subject. We modify a multiresolution knowledge distillation neural network model, the state-of-the-art anomaly detection model to a multiresolution knowledge distillation network model with asymmetric inputs, which uses grayscale maps to align the features of color maps in the feature space, to help improve otolith anomalies detection. Our fine-tuned anomaly detection network obtains a better anomaly identification performance with a Receiving Operating Characteristic Area Under the Curve value of 0.9843. Our result shown that multiresolution knowledge distillation networks can efficiently identify abnormal otolith image sample, which is of great importance for conducting otolith-based science.

The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the epithelium, muscles, and elements of connective and nerve tissue. The integument acts as a physical barrier between the external environment and the internal environment that serves to protect and maintain the body of the animal. The body of nudibranch mollusks undergo significant changes during ontogenesis, with the subepidermal space changing as the mollusk grows. As the extracellular subepidermal matrix is modified, the number of collagen fibers increases, muscles and nerves develop, and calcite spicules appear and grow. Yet, specific knowledge pertaining to the transformation of the epithelium is absent. In the present work, the ontogenetic dynamics of the surface epithelium of nudibranch mollusks are traced for the first time using Onchidoris muricata (O. F. Müller, 1776) during the postlarval stages of development. Ontogenetic changes in the epithelium of O. muricata were studied using a complex set of morphological methods. According to our data, the degree of modification to the epithelium in ontogenesis depends on individual body parts and is not consistent throughout. First x-cells were recognized as the probable precursors to sclerocytes.

Reproduction in female mammals is characterized by major changes in steroid hormone concentrations, which can be linked to fluctuations in energy expenditure (EE). Estradiol and cortisol can increase EE and metabolic rates (MRs), but knowledge on MR changes during the estrous cycle and gestation is scarce for many species. This also applies to the domestic guinea pig, a species exhibiting an exceptional estrous cycle among rodents. In this study, MRs were measured through oxygen (O₂) consumption in female guinea pigs during different reproductive stages. Mean O₂ consumption over 2.5 h, resting metabolic rate (RMR, lowest and most stable O₂ consumption over 3 min), body mass, fecal estrogen and progesterone, and saliva cortisol concentrations were measured in twelve female guinea pigs in a repeated measurements design during diestrus, estrus, and the second trimester of gestation. In estrus, body mass was significantly lower and estrogen and cortisol concentrations were significantly higher compared to diestrus and gestation. Mean O₂ consumption and RMR both were significantly increased in estrus compared to diestrus. Additionally, a positive effect of body mass on MRs detected during diestrus and gestation was not found during estrus. Mean O₂ consumption was also higher during gestation compared to diestrus, and a significant increase in cortisol concentrations during the 2.5-h MR measurement was recorded. The results indicate that estrus in guinea pigs is energetically demanding, which probably reflects catabolic effects of estrogens and cortisol that uncoupled MRs from body mass. Knowledge on the energetic requirements associated with different reproductive stages is important for future physiological and behavioral studies on female guinea pigs.

Physogastric termite queens are characterized by a notorious enlargement of the abdomen triggered by an equal development of the ovaries. Other physogastry-related modifications have been reported on the fat body, cuticle, midgut, tracheal system, and hemolymph. Surprisingly, modifications on the lateral oviducts of these females, important sites for ovulation and egg transport, have received little attention. Here we took advantage of the high fecundity of physogastric queens in three termitid species to evaluate ovary development and also to compare the morphophysiological features of the lateral oviducts between early-mated and physogastric queens of Cornitermes cumulans. Older queens show well-developed ovaries, with numerous ovarioles connected to the lateral oviducts through pedicels. At these sites, several corpora lutea were observed, residual follicle cells from previous ovulation events. Such features were absent among early-mated queens and reflect then the maturity and ageing of the queens. Histological and histochemical analyses indicated that secretory activity of the lateral oviducts was also restricted to physogastric queens, in which proteins, but not polysaccharides, are secreted into the oviduct lumen. The likely function of these proteins, based on previous studies, is to lubricate the lateral oviducts and stimulate muscular contractions to the egg transport. The physogastry of termite queens is a notorious feature, characterized by several body modifications, especially concerning the ovaries. Our results shed light on the physogastry-related changes in the lateral oviducts of termite queens, as their increasing secretory activity is in agreement with the high number of eggs produced and transporting through these structures. Thus, such changes correspond to an important step allowing the high egg-laying rate shown by physogastric termite queens.

An organism’s ability to identify goals within their environment, orient towards those goals, and successfully navigate to them are critical to all aspects of survival. Long-jawed orb weavers (Tetragnatha elongata) occupy riparian zones and perform orientation behaviors when displaced from this habitat onto the water. Spiders prefer to move toward the closest shoreline, regardless of release location, likely to avoid predation from fish. In this study, we conducted a series of investigations to determine the mechanism by which these spiders rapidly achieve zonal recovery. Occlusion experiments indicate that spiders use visual information to identify characteristics of the riparian habitat and navigate to shelter. While environmental characteristics such as color, contrast, and the sun’s position do not appear to factor into this orientation behavior, the polarization of light appears critical. We propose that the polarization of light reflecting off the water’s surface acts as a water detector and the absence of such at the edges of the pond (or via experimental induction) serves as a visual reference for the closest suitable habitat.

Dispersal is an important factor that determines the potential for colonization to pioneer sites. Although most decapods employ seaward migration for reproduction with a planktonic larval phase, true freshwater crabs spend their entire life cycle in freshwater. Therefore, it is expected that genetic regionality can be easily detected. In this study, we focused on true freshwater crabs, Geothelphusa Stimpson, 1858. Herein, we reveal the evolutionary history and dispersal patterns of freshwater crustaceans. We collected and genetically analyzed 283 specimens at 138 localities across the Japanese Islands. Phylogenetic analyses were conducted on the combined dataset (mtDNA COI, 16S, and nDNA ITS1, histone H3 regions) and the data set based on the mtDNA COI region. The phylogenetic relationships detected 10 clades that were highly monophyletic. The highlights of this study were the discovery of several cryptic species or undescribed species, and the completely different heterogeneous dual dispersal pathways within a single species; i.e., both land and ocean routes. Although it was concluded that Japanese crabs are basically genetically divided by straits, strong evidence for dispersion via ocean currents was also detected (i.e., a “sweepstake”). It was also confirmed that Geothelphusa dehaani (White, 1847) could survive in seawater.

Directional cranial asymmetry is an intriguing condition that has evolved in all odontocetes which has mostly been associated with sound production for echolocation. In this study, we investigated how cranial asymmetry varies across odontocete species both in terms of quality (i.e., shape), and quantity (magnitude of deviation from symmetry). We investigated 72 species across all ten families of Odontoceti using two-dimensional geometric morphometrics. The average asymmetric shape was largely consistent across odontocetes – the rostral tip, maxillae, antorbital notches and braincase, as well as the suture crest between the frontal and interparietal bones were displaced to the right, whereas the nasal septum and premaxillae showed leftward shifts, in concert with an enlargement of the right premaxilla and maxilla. A clear phylogenetic signal related to asymmetric shape variation was identified across odontocetes using squared-change parsimony. The magnitude of asymmetry was widely variable across Odontoceti, with greatest asymmetry in Kogiidae, Monodontidae and Globicephalinae, followed by Physeteridae, Platanistidae and Lipotidae, while the asymmetry was lowest in Lissodelphininae, Phocoenidae, Iniidae and Pontoporiidae. Ziphiidae presented a wide spectrum of asymmetry. Generalized linear models explaining magnitude of asymmetry found associations with click source level while accounting for cranial size. Using phylogenetic generalized least squares, we reconfirm that source level and centroid size significantly predict the level of cranial asymmetry, with more asymmetric marine taxa generally consisting of bigger species emitting higher output sonar signal, i.e. louder sounds. Both characteristics theoretically support foraging at depth, the former by allowing extended diving and the latter being adaptive for prey detection at longer distances. Thus, cranial asymmetry seems to be an evolutionary pathway that allows odontocetes to devote more space for sound-generating structures associated with echolocation and thus increases biosonar search range and foraging efficiency beyond simple phylogenetic scaling predictions.

Ovaries in earthworms belonging to the family Megascolecidae are paired structures attached to the septum in the anterior part of the XIII segment. They are fan to rosette shaped with numerous rows of growing oocytes, known as egg strings, radiating from the ovary center towards the segmental cavity. The histological and ultrastructural ovary organization in megascolecids and the course of oogenesis remain unknown. The paper presents the results of light and electron microscopy analyses of ovaries in six megascolecid species, three from the genus Amynthas and three from Metaphire. Both parthenogenetic and sexually reproducing species were included in the study. The organization and ultrastructure of ovaries in all studied species are broadly similar. Considering the histological organization of ovaries, they could be divided into two zones. Zone I (proximal, close to the connection with the septum) is tightly packed with germline and somatic cells. Germ cells are interconnected via intercellular bridges and thin strands of the central cytoplasm (known as cytophore) and form syncytial cysts. Cysts unite oogonia, early meiotic cells (till diplotene), and clustering cells develop synchronously. During diplotene, interconnected cells lose developmental synchrony; most probably, one cell per cyst grows faster than others, detaches from the cysts, and becomes an oocyte. The remaining cells grow slightly and are still interconnected via the thin and reticular cytophore; these cells are considered nurse cells. Zone II has a form of egg strings where growing oocytes are isolated one from another by thin somatic cells and form short cords. We present the ultrastructural details of germline and somatic cells. We propose the term "Amynthas" type of ovaries for this ovary organization. We suppose that such ovaries are characteristic of other megascolecids and related families.

The phenomenon of exocrine secretion via nervous cells into the host tissue has been discovered in cestodes. In five cestode species of different orders specialized “cup-shaped” free nerve endings located in the tegument have been found. Their ultrastructure is characterized by the presence of a septate junction, a thin support ring and neurosecretory vesicles 90–110 nm in diameter, which are secreted onto the surface of the tegument through a thin pore. The phenomenon is referred to in this article as the neuro-exocrine secretion. We observed a direct relationship between neurosecretory processes in the deep subtegument and free endings in a series of ultrathin sections in two species. The peripheral neurosecretory neurons of species studied are characterized by similar ultrastructural features: size and location; diameter of neurosecretory granules; absence of microtubules and mitochondria in the neurites. The size of neurosecretory granules has been found to decrease from perikaryon towards neurosecretory terminals that lead to the tegument. In two species, we examined the neurosecretion during incubation in the host's blood serum. Depending on the time of incubation we have shown the changes a) in the diameter of the cup-shaped endings, b) in the number of secretory vesicles in the endings; c) changes in number and diameter of neurosecretory vesicles in the processes of neurosecretory neurons in the subtegument. The detected changes differ in D.dendriticus and L.interrupta and, taken together, indirectly confirm the secretory specialization of the cup-shaped endings. Supposed targets for the neurosecretory neurons in the studied cestodes are the following: (a) eccrine frontal gland ducts, especially their terminal regions involved in the release of secretory products; (b) longitudinal and circular muscles in the subtegument region; (c) the basal membrane of the tegument. Besides the discovered secretion vesicles through the cup-shaped terminals, we observed vacuoles derived from the basal membrane of the tegument containing extracellular substances released into the host tissue. Their possible role in the release of neurosecretory substances is discussed. Considering the data acquired via immunocytochemical methods, an assumption about involvement of FMRFamide-like related peptides (FaRPs) in the neuro-exocrine secretion is proposed. Possible functions of the neuro-exocrine secretion are discussed in the context of host-parasite interactions.