Peltogasterella Gracilis Research Articles

Transcriptomic analysis of sexually dimorphic cypris larvae of the rhizocephalan barnacle Peltogasterella gracilis

Peltogasterella gracilis (Cirripedia: Rhizocephala), a crustacean parasite of hermit crabs, displays genotypic sex determination. Its larvae are planktonic, and female larvae settle on the host. Subsequently, the females control the host's behavior by spreading a root-like structure called “the interna” within the host's body, and form sacs containing eggs called “the externae” outside the host's body. On the other hand, male larvae settle on immature externae and become dwarf males. The cypris larvae of P. gracilis show sexual dimorphism in size and morphology. However, there is no understanding of the molecular mechanisms underlying the sexual dimorphism observed at the larval stage. Here, we conducted a transcriptome analysis and compared the expression of genes in male and female cyprids to better understand their sexual differentiation and settlement processes. A total of 2870 differentially expressed transcripts, comprising 456 female- and 2414 male-biased transcripts were identified. Among the male-biased ones, ionotropic glutamate receptor-, heat shock protein-, acetylcholine-, and homeobox-, cuticle-related transcripts were included. Additionally, 29 gene ontology terms were associated with the sex-specific traits. The present study improves our understanding of sex determination, sexual differentiation, and settlement processes of rhizocephalans.

Functional role of lacunar and muscular systems in the externa of Peltogasterella gracilis (Cirripedia: Rhizocephala).

One of the most conspicuous traits of parasitic organisms is a well-developed reproductive system. In Rhizocephala ("Crustacea": Cirripedia) it is believed to be nested in the externa-a "reproductive part" located outside of the host. However, it is not clear how nutrients are transported to the externa. Several authors described a system of lacunae in the externa, and muscular contractions probably enable transport through these cavities. The aim of our study was to visualize (using microcomputed tomography and confocal laser scanning microscopy) and describe lacunar and muscular systems in the externa of Peltogasterella gracilis (fam. Peltogasterellidae). The lacunar system consists of "ventral" lacuna and several protrusions. The "ventral" lacuna is probably responsible for visceral mass nutrition, and mantle protrusions are associated with the mantle nutrition. The gross organization of the muscular system mostly corresponds to previous descriptions in other rhizocephalan species. Nonetheless, we observed several features of the externa morphology that had not been described before such as a muscular thickening in the proximal externa's part and a stalk plug disk. The muscular thickening might play a role of a propulsatory organ, helping to transport liquid through the lacunar system. The plug disk might fill the hole in the host's cuticle after the old externa drop off. The results allow us to make first assumptions on transport mechanisms in Rhizocephala.

Variations in life cycle and seasonal sex ratio in the rhizocephalan Peltogasterella gracilis (Boschma, 1927) (Cirripedia: Rhizocephala: Peltogasterellidae)

Abstract Most individuals of the rhizocephalan Peltogasterella gracilis (Boschma, 1927) produce only male (larger) or female (smaller) offspring, but some mixed-sex broods appear in autumn. Such variability may be an adaptation to the seasonally changing availability of hosts (for female larvae) and conspecific females (for male larvae), but details of the seasonal variation in the sex ratio and its ultimate causes have not been fully studied in P. gracilis. We studied the life cycle, host availability, and seasonal sex-ratio variation in P. gracilis by samplings from spring to autumn in 2017–2020 in Otaru, and additionally from winter to spring of 2007 in Oshoro Bay, Hokkaido, northern Japan. We measured its prevalence on the hermit crab Pagurus lanuginosus De Haan, 1849, the number of males per externa, the proportion of externae brooding different embryonic stages, and embryo size that are linked to sex. The prevalence was about 20% in most of the sampling period. The number of males per externa was 0.01–0.74 in June 2018–2020, but increased in later months to nearly 1.0. Eyed embryos and nauplii before hatching were common from June or July to September, but they were rare in other seasons. Female embryos were observed in all sampling periods, but male embryos were not found in July or August, by which time most females already have males implanted within their receptacles. It is suggested that P. gracilis releases both female and male larvae according to the availability of unparasitized hosts and of virgin externae, respectively.

Muscular system of Peltogasterella gracilis – A rhizocephalan with the modular type organization of interna

Rhizocephala is a group of highly modified parasitic crustaceans. The body of an adult female is formed de novo, and lacks most traits of free-living crustaceans. Despite the large number of studies dedicated to different aspects of rhizocephalan biology, the structure of the interna of these parasites is still poorly understood. The muscular systems specifically were described only for representatives of three families. The aim of our study is to visualize and describe the muscular system in the interna of Peltogasterella gracilis from the family Peltogasterellidae. P. gracilis has a colonial type of organization, with a common part of the interna and numerous externa-bearing modules. Interestingly, the muscular system has dissimilar organization in different parts of the interna. Muscular system in modules resembles that of Peltogaster paguri, while in the common part of the interna it's more similar to the muscular system of sacculinids and polyascids. We propose that the muscular system of rhizocephalans is a new structure in terms of evolution, and as such can be easily modified in respect to the functional characteristics of the different interna's parts.

Specialised rootlets of Sacculina pilosella (Rhizocephala: Sacculinidae) used for interactions with its host's nervous system

Parasitic rhizocephalan barnacles induce morphological, physiological, and behavioural changes in their hosts. The mechanisms of these intimate host-parasite interactions remain unknown. We have shown previously that rootlets of the internae of Peltogasterella gracilis and Peltogaster paguri penetrate the ganglion's envelope of their hermit crab hosts and form specialised structures in the ganglion periphery, the so-called goblet-shaped organs. Here, we examine the gross morphology and ultrastructure of these goblet-shaped organs in the interna of Sacculina pilosella. They consist of three layers of cells; in the intermediate layer of the organs, unusual lamellar bodies and muscle cells were found. Extensive degeneration of the host nervous tissue was observed in the funnel of the goblet-shaped organs. We conclude that the ability to penetrate into the host's nervous tissue could be a common trait in rhizocephalans. The goblet-shaped organs may play a key role in the host-parasite relationships by enabling the parasite to influence the host via hormones and neurotransmitters.

Specialized structures on the border between rhizocephalan parasites and their host\u2019s nervous system reveal potential sites for host-parasite interactions

Rhizocephalan barnacles are a unique group of endoparasitic crustaceans. In their extreme adaptation to endoparasitism, rhizocephalan adults have lost almost all features of their free-living relatives but acquired an outstanding degree of control over the body of their hosts (mostly decapods). The subtle influence exercised by rhizocephalans on the physiology, morphology and behaviour of their hosts is a vivid example of the most intimate host-parasite interactions but their mechanisms are very poorly known. In this study we examined the morphology and the adaptive ultrastructure of the organs invading the nervous system of the host in two rhizocephalan species from the families Peltogastridae, (Peltogaster paguri) and Peltogasterellidae (Peltogasterella gracilis). We found two essentially different types of structures involved in interactions of these two rhizocephalans with the nervous system of their hosts: modified rhizocephalan rootlets lying inside the ganglia and the neural fibres of the host enlacing the trophic rootlets of the parasites. We suggest that both these structures may be highly specialized tools allowing the parasite to interact with the host on the humoral level via neuromediators, hormones, attractants and trophic factors.

Diversity of Parasitic Peltogastrid Barnacles (Crustacea: Cirripedia: Rhizocephala) on Hermit Crabs in Korea.

We performed a diversity study on parasitic barnacles (Crustacea: Cirripedia: Rhizocephala: Peltogastridae) that parasitize hermit crabs in Korea. Their morphological, ecological, molecular (cytochrome c oxidase subunit I, 16S rRNA), and biogeographical characteristics were examined. Three species were identified based on GenBank sequences and the external morphology of the externa. In addition, this study proposes four new candidate species. This is the first report on the family Peltogastridae from Korea. Six hermit crab species were found to be new hosts to peltogastrids. Korean peltogastrids are less prevalent on their host hermit crabs than those from Japan are, especially in the west coast of Korea. Peltogasterella gracilis is widely distributed throughout Korea, Peltogaster lineata is located on the east coast, and Peltogaster postica is only located on Jeju Island.

The Parasitic Fauna of Common Species of Hermit Crabs of Vostok Bay (Sea of Japan)

The parasitic fauna of common species of hermit crabs was investigated in Vostok Bay (the northwestern Sea of Japan). Pagurus proximus and Areopaguristes hirsutimanus had no parasites. The average prevalence of rhizocephalan infestation in other five species of hermit crabs ranged from 5.67 to 20.83%. The prevalence of the isopod Parapseudione lata on hermit crabs did not exceed 1%, the prevalence of infestation with the isopod Athelges takanoshimensis was significantly higher, reaching 14.58% in Pagurus middendorffii. Parasitism by the isopod P. lata on the hermit crabs Pagurus minutus and P. ochotensis, as well as parasitism by the rhizocephalan Peltogaster reticulata on P. minutus were recorded for the first time. Several variants of simultaneous infestation with two parasitic species were found. The decline in the abundance of P. middendorffii accompanied by the high prevalence of parasites, primarily the colonial rhizocephalan Peltogasterella gracilis, suggests that parasite invasion may play a more significant role in regulating the abundance of hermit crabs than was previously assumed.

Peltogasterella sensuru n. sp. (Crustacea: Cirripedia: Rhizocephala) from off Okinawa Island (Ryukyu Archipelago, Japan) with remarks on its single brood externae.

Peltogasterella sensuru n. sp. infests Pagurixus hermit crabs inhabiting rocky shores off Okinawa Island (Ryukyu Archipelago, Japan). This species is clearly distinguishable from Peltogasterella gracilis (Boschma, 1927): the stalk emerges from the middle part of the externa in the present species and P. sulcata (Lilljeborg, 1859), while the stalk in P. gracilis emerges from the posterior end of the externae. The new species differs from P. sulcata based on the morphology of the mantle aperture. Peltogasterella sensuru n. sp. repeatedly produces single brood externae that have not been previously observed in species belonging to the suborder Kentrogonida Delage, 1884. We also determined partial sequences of the COI gene and 16S rRNA gene of the new species for use as molecular markers for species identification.

10.1007/s11179-008-1001-8

Original and literature data supporting the evolutionary conservation of the morphofunctional organization of totipotent cells of germ and stem lineages in metazoan animals are reviewed. We studied stem cells of the colonial rhizocephalans, Peltogasterella gracilis, Polyascus polygenea and Thylacoplethus isaevae, the turbellarian Dugesia tigrina, the colonial hydroid Obelia longissima, and cultured embryonic stem cells of mouse. The typical germinal granules of germ plasm, selective expression of the activity of alkaline phosphatase and of proliferating cell nuclear antigen (PCNA), which are known as markers of stem and primary germ cells of vertebrates, and the specific expression of the protein product of the vasa gene in cells of rhizocephalans, which is a marker of cells of germ and stem lineages of various metazoans, specified the stem cells of invertebrates of such different taxa. The self-renewing pool of totipotent stem cells is the cellular basis of the reproductive strategy, including sexual and asexual reproduction; such cells share morphofunctional features of embryonic stem and germline cells of Metazoa.

Fractal and chaotic patterns in animal morphology

In the review the spatial organization of cells, cell ensembles, tissues and metazoan body are considered using the concepts of fractal geometry, topology and dynamic chaos theory. We investigated both the scenario of transition from chaos into order during self-organization of cells in vitro and the reverse scenario of transition from order to chaos in the fractal morphogenesis of metazoan cell systems. Chaotic features in animal morphology were identified and quantified. Fractal morphogenesis was studied using epithelial branching channels of gastrovascular system in the scyphomeduse Aurelia aurita and tracheal gill system in the mayfly larvae Siphlonurus immanis and Parameletus chelifer, as well as structures of colonial interna in rhizocephalan crustaceans Peltogasterella gracilis and Polyascus polygenea. It was shown that completely identical fractal patterns do not occur even within a single animal body with radial or bilateral symmetric, functionally equivalent repetitive modules. Fractal dimension was used to quantify the spatial complexity of neuron morphology in central nervous system of the fishes Pholidapus dybowskii, Oncorhyhchus keta and Oncorhyhchus masou. During ontogenesis of Oncorhyhchus masou the values of fractal dimension and linear morphometric indicators were rising in studied neuron groups. Probably biological morphogenesis with chaotic fractal regime had an advantage in evolution, providing morphofunctional variability, plasticity and adaptability to unpredictable environmental changes.

Stem cells in reproductive strategy of asexually reproducing invertebrates

Original and literature data supporting the evolutionary conservation of the morphofunctional organization of totipotent cells of germ and stem lineages in metazoan animals are reviewed. We studied stem cells of the colonial rhizocephalans, Peltogasterella gracilis, Polyascus polygenea and Thylacoplethus isaevae, the turbellarian Dugesia tigrina, the colonial hydroid Obelia longissima, and cultured embryonic stem cells of mouse. The typical germinal granules of germ plasm, selective expression of the activity of alkaline phosphatase and of proliferating cell nuclear antigen (PCNA), which are known as markers of stem and primary germ cells of vertebrates, and the specific expression of the protein product of the vasa gene in cells of rhizocephalans, which is a marker of cells of germ and stem lineages of various metazoans, specified the stem cells of invertebrates of such different taxa. The self-renewing pool of totipotent stem cells is the cellular basis of the reproductive strategy, including sexual and asexual reproduction; such cells share morphofunctional features of embryonic stem and germline cells of Metazoa.

Stem cells in the reproductive strategy of colonial rhizocephalan crustaceans (Crustacea: Cirripedia: Rhizocephala)

Summary In vivo, histological, histochemical, immunochemical and ultrastructural investigations were performed of the colonial internae of Peltogasterella gracilis, Polyascus (Sacculina) polygenea, and Thylacoplethus isaevae (all infesting decapods). It was shown that asexual reproduction in these species occurs through the budding of stolon-like structures. Undifferentiated stem cells were found inside the stolons. They take part in the morphogenesis of the earliest buds, and later migrate to the developing ovary as primary germ cells. The stem cells in P. polygenea, P. gracilis and Th. isaevae selectively express alkaline phosphatase activity, a well known histochemical marker for mammalian embryonic stem cells in vivo and in vitro. It is shown in P. gracilis that stem cells also selectively express proliferating cell nuclear antigen (PCNA), a cellular marker for cell reproduction. The reproductive strategy in colonial rhizocephalans includes a three-level cascade: asexual reproduction by budding in interna; repeated development of multiple externae; and, in some cases, repeated cycles of sexual reproduction in each externa, resulting in large numbers of hatching larvae and allowing the parasite to infest a large proportion of the host population. Thus, sexual and asexual generations alternate in the life-cycle of the colonial species; stem cells evidently contribute the source of cells in asexual as well as sexual reproduction.

Effects of temperature and salinity on the larvae of two species of rhizocephalan (Crustacea: Cirripedia)

Summary Responses of larvae of two rhizocephalan species to changes in seawater temperature and salinity were studied under laboratory conditions. Peltogasterella gracilis parasitizes the hermit crab Pagurus pectinatus, which occurs at stable salinity and gradually changing temperature in summer. Sacculina polygenea is a parasite of the crab Hemigrapsus sanguineus, which lives in the intertidal zone in summer where salinity and temperature can fluctuate during the day. The development of both species is comprised of five naupliar stages and the cyprid stage, and it was considered successful if more than 50% of the nauplii attained the cyprid stage. P. gracilis nauplii successfully developed at 12–20°C and 30–34‰, but at 22°C successful development occurred in a narrower salinity range (32–34‰). All nauplii died both at 25°C and in 26‰. S. polygenea nauplii successfully reached the cyprid stage at higher temperatures (18–25°C) and a wider salinity range (18–34‰) than P. gracilis nauplii, but at 12°C and 16‰ larval development of S. polygenea was suppressed. Under favorable conditions, naupliar development lasted 3.5 days in P. gracilis and 2–3 days in S. polygenea. The cyprids of both rhizocephalan species demonstrated a greater resistance to temperature and salinity changes than nauplii. However, P. gracilis cyprids were active in a narrower salinity range (16–34‰), as compared to S. polygenea cyprids (8–34‰). Under favorable conditions the cyprids of both species survived for 6 to 10 days.

Adaptive Responses of the Larvae of Cirripede Barnacle Peltogasterella gracilis to Changes in Seawater Temperature and Salinity

The responses of the larvae of the cirripede barnacle Peltogasterella gracilis (Crustacea: Cirripedia: Rhizocephala) that parasitizes the hermit crab Pagurus pectinatus to different combinations of seawater temperature (25, 22, 20, 16, and 12°C) and salinity (from 34 to 8‰) were studied in a laboratory. The nauplii of P. gracilis completed the entire cycle of development at 22 to 12°C in a narrow range of salinity (from 34 to 28‰), which agrees well with the environmental conditions of the crab hosts' habitat. At favorable temperatures (22–20°C) and salinity (34–28‰), the nauplii reached the cypris stage in 88 ± 2 h, while at 12°C and 34–30‰, the naupliar development took 156 ± 5 h. The cypris larvae appeared more resistant compared with the nauplii, in terms of changes in both the temperature and salinity of seawater. They actively swam at all experimental temperatures and in the salinity range of 34–18‰. At temperatures (22–16°C) and salinities (34–24‰) favorable for the cyprids, their longevity in plankton equaled 6–10 days. Thus, the nauplii of P. gracilis is the more vulnerable stage of development in the life cycle of this parasitic barnacle. The tolerance against changes in environmental factors is due to the adaptive capabilities of parasitic larvae and the environmental conditions in the habitats of its host, a typical marine crustacean. The insignificant parasitization rate of the hermit crab by its rhizocephalan parasite may be explained by the death of the nauplii of P. gracilis, which occurs when they enter to the surface water layer.

Organization of the Interna of the Rhizocephalan Barnacle Peltogasterella gracilis

We carried out an in vitro histological and TEM investigation of the organization of the interna of Peltogasterella gracilis(Crustacea: Rhizocephala), a parasite of the hermit crab. The colonial interna of P. gracilisincludes a reproductive system with multiple nuclei (externa rudiments) and a trophic system of absorbing lampbrush and transportation canals. The nucleus forms a cluster of embryonic stem cells. In the distal parts of the trophic system, there are cells that function in the absorption, processing, and storage of trophic substances. Cells filled with trophic resources disintegrate (evidently by apoptosis), releasing trophic substances and cell remnants into the canal cavity formed through this process. The parasitic phase of the P. gracilislife cycle is characterized by the loss of the basic morphological features and complete pattern of organization of the arthropods and by chaos and fractalization in the interna.

STUDIES ON THE SEXUAL ORGANIZATION OF THE RIHZOCEPHALA. III. THE MODE OF SEX-DETERMINATION IN PELTOGASTERELLA

1. The adult females of the rhizocephalan, Peltogasterella gracilis (Boschma), although they appear similar, are in reality two kinds, large-egg-producing and small-egg-producing females.2. The large eggs develop into large larvae which function as males (larval cypris males). The small eggs develop into small larvae which give rise to adult females.3. In the metaphase plate of the first maturation division of the large male-producing egg 15 bivalent chromosomes are seen, while in the small female-producing egg a univalent chromosome is found beside 15 bivalent chromosomes.