Taxonomy of the European Hydra (Gnidaria: Hydrozoa): a re-examination of its history with emphasis on the species H. vulgaris Pallas, H. attenuata Pallas and H. circumcincta Schulze

The name Hydra attenuata Pallas is currently applied to the wrong animal. The common brown polyp, which is widely called H. attenuata, was described by Pallas (1766) as Hydra vulgaris. The name H. attenuata Pallas originally referred to an uncommon pale polyp, currently known as H. circumcincta Schulze. The history of this confusion is analysed here. The taxonomy of hydra was in disarray during the 18th and 19th centuries, and was clarified in 1917 with the monograph of Schulze. But Schulze misapplied the name for the common hydra, H. vulgaris, to an unusual form and thus was led to assign the name of a rare hydra, H. attenuata, to the common type. Schulze redescribed the rare, pale hydra that Pallas had named H. attenuata as H. circumcincta. The correct name of the common European brown, stalkless hydra is thus H. vulgaris Pallas, 1766. The name H. attenuata has priority for the uncommon pale hydra, but because of disuse of this application of the name, the pale hydra should be recognized by the current, generally accepted binominal H. circumcincta Schulze, 1914.     

Hydra of Hawaii: phylogenetic relationships with continental species

The presence of freshwater hydra in the Hawaiian Islands, over 3,700 km from the nearest continental margin, provokes the question of how these animals could reach the islands. We examined three islands for hydra and found two species (the brown hydra, Hydra vulgaris Pallas 1766, and green hydra, H. viridissima Pallas 1766) present at multiple locations on Oahu and Kauai, and at a single site on Hawaii. Phylogenetic analysis based on the internal transcribed spacer (ITS1 and ITS2) regions of ribosomal DNA indicates that all collected strains of brown hydra were closely related to each other—consistent with a single introduced origin. The analysis also shows that all sampled Hawaiian brown hydra fall within a specific clade of H. vulgaris. This clade is sister to a North American clade and nested within a deeper North/Central America clade. The clade with all the Hawaiian brown hydra includes also individuals from Southern California, suggesting a Californian origin for the brown Hawaiian hydra. Hawaiian hydra were probably transported to the islands by man.     

普通水螅(无鞘螅目,水螅科)中国一新纪录种

对采自中国广东省珠江流域(114°E,23°N)的一种淡水水螅进行连续两年的培养与观察,并扩增了其线粒体细胞色素氧化酶亚基Ⅰ(COⅠ)的基因序列.通过形态学分析及CO Ⅰ基因序列的鉴定确定其为普通水螅Hydra vulgaris Pallas,1766,为中国一新纪录种.     

New observations on green hydra symbiosis

New observations on green hydra symbiosis are described. Herbicide norflurazon was chosen as a "trigger" for analysis of these observations. Green hydra (Hydra viridissima Pallas, 1766) is a typical example of endosymbiosis. In its gastrodermal myoeptihelial cells it contains individuals of Chlorella vulgaris Beij. (KESSLER & HUSS 1992). Ultrastructural changes were observed by means of TEM. The newly described morphological features of green hydra symbiosis included a widening of the perialgal space, missing symbiosomes and joining of the existing perialgal spaces. Also, on the basis of the newly described mechanisms, the recovery of green hydra after a period of intoxication was explained. The final result of the disturbed symbiosis between hydra and algae was the reassembly of the endosymbiosis in surviving individuals.     

Life history trade-offs and stress tolerance in green hydra (Hydra viridissima Pallas 1766): the importance of nutritional status and perceived population density

Clonally reproducing animals, such as freshwater hydra, can achieve very quick population growth, potentially resulting in high density when dispersal is limited. The reproductive value of any offspring produced clonally in such a high density population is low because of the strong competition for food. Therefore, animals experiencing such conditions should allocate their resources to self-maintenance, to increase survival chances. Increased allocation to self-maintenance in turn should enable animals to withstand higher levels of genotoxic stress. To test this prediction, we exposed green hydra (Hydra viridissima Pallas 1766) to a perceived high density (by keeping them in crowded culture medium) or low density (fresh culture medium) without altering food availability. We also manipulated nutritional status (by starving animals for different time periods) and previous exposure to mild stress in a full factorial experimental design. At the end of the experiment we exposed animals to a high concentration of hydrogen-peroxide and scored stress tolerance. We found that stress tolerance is greatly elevated in animals perceiving high density, confirming our prediction. Stress tolerance decreased in animals starved for a few days, suggesting that the ability to maintain an elevated stress tolerance function has nutritional costs and is possible only when resource availability is high. On the other hand, previous exposure to mild stress had a small effect on the ability to tolerate subsequent exposure to stress, and only in the low density treatment group. Thus, stress tolerance in hydra is dynamically modulated in response to social, environmental and nutritional cues.     

中国绿水螅分子系统发生地位的初步探讨

目的:初步探讨中国绿水螅(Hydra sinensis)分子系统发生地位以及水螅属内部各类群系统发生关系。方法:采用酚-氯仿法提取中国绿水螅总DNA,扩增线粒体COI和16S r RNA基因片段并进行DNA序列测定,再利用Clustal及MEGA等生物信息学分析软件进行系统发生分析。结果:在本研究重建的所有系统发生树中,中国绿水螅始终与绿水螅Hydra viridissima的不同种群一起构成绿水螅单系群。同时,棕色水螅群的单系性被基于COI基因的NJ树以及基于16S r RNA基因的NJ树和ML树支持,唯独基于COI基因的ML树不支持棕色水螅群的单系发生。在基于COI基因的ML树中纤弱水螅族在系统树的基部独立为一支系,而绿水螅群和其他棕色水螅群水螅一起组成另一支系,提示纤弱水螅族水螅的系统发生地位值得进一步探讨。值得注意的是,根据本文的结果,棕色水螅群内3族的划分仍然有一定疑问。基于COI基因的NJ树和ML树支持普通水螅族、寡水螅族和纤弱水螅族各自族内的单系发生,但16S r RNA基因的NJ树和ML树中仅普通水螅族水螅聚为单系群,而寡水螅族和纤弱水螅族水螅各自并非单系发生。结论:把水螅属划分为绿水螅群及棕色水螅群有一定的合理性,但棕色水螅群内寡水螅族、普通水螅族和纤弱水螅族3族的划分还有待商榷。     

Environmental condition related reproductive strategies and sex ratio in hydras

Kaliszewicz, A. and Lipińska, A. 2011. Environmental condition related reproductive strategies and sex ratio in hydras. —Acta Zoologica (Stockholm) 00 :1–7. Temperature and food supply appeared to affect sex ratio, sex composition and percentage of sexual individuals in three Hydra species: Hydra vulgaris, Hydra circumcincta and Hydra viridissima. We found three sexes present: females, males and hermaphrodites depending on environmental conditions. Hydra vulgaris appeared to be a species with a temperature‐dependent sex determination (TSD). The males and hermaphrodites were present only under rising temperatures, whereas females were observed exclusively at lowering temperatures. Hydras reproduced asexually at constant room temperature. Unlimited food affected sex ratios and induced the presence of males in H. circumcincta at lowering temperatures. Thus, H. circumcincta may be recognised as another Hydra species in which sex is determined by environmental factors (ESD). Under rising temperatures, the number of hermaphroditic individuals was higher when food supply was unlimited in all three species, indicating that hermaphrodites may need more energy to produce both male and female gonads. Both temperature changes and food supply positively affected asexual reproductive strategies in hydras, especially budding rates. Hydra circumcincta appeared to be less agile than other hydras and able to self‐fertilise. It is likely that self‐fertilisation is an adaptation to the low probability of meeting a mate belonging to the other clone.     

Bombesin-like immunoreactivity in the nervous system of hydra

Summary With immunocytochemical methods, nerve cells have been detected in Hydra attenuata containing bombesin-like immunoreactivity. These nerve cells are located in the ectoderm of all body regions of the animal and are especially abundant in basal disk and tentacles. Radioimmunoassay of extracts of hydra demonstrated at least 0.2 pmol/g wet weight of bombesinlike immunoreactivity. The immunoreactive material elutes from Sephadex G-50 in a similar position to synthetic bombesin. The data show that bombesin-like peptides are among the phylogenetically oldest neuropeptides found so far.     

强壮水螅的特征及其与寡水螅的种间差别问题

一种广泛分布于黑龙江省的大型具柄水螅被暂定为强壮水螅Hydra robusta(IT(?) 1947)。这一中国品系与IT(?)(1947)在日本报告的新种主要特征相同,包括具有精巢乳头。只是精巢乳头不稳定。在实验室条件下第一次有性生殖时每个雄体都发生精巢乳头,但第二次有性生殖时,同一群的后代可全部失去精巢乳头。这是介于强壮水螅与寡水螅Hydra oligactis Pallas(1766)之间的中间性状。从而导致作者做出结论,认为过去其他学者所主张的,以精巢乳头的有无做为鉴别特征来区分强壮水螅和寡水螅是不可靠的。因此,本文又检验了此种水螅的体细胞染色体,证明2n=30,其中第二对染色体上有明显近中位置的次缢痕,最小染色体的长度为最大染色体长度的二分之一以上。这些可做为此种水蝗的鉴别特征。对Niiyama(1944)和Datta(1970)在寡水螅上所做的染色体研究也做了比较及讨论。     

Both the epithelial cells and the nerve cells are involved in the head inhibition properties in Hydra attenuata

The aberrant, a morphological mutant of Hydra attenuata, has been shown to have altered inhibition properties(D. I. Rubin and H. R. Bode, 1982, Develop. Biol. 89, 316–331). Based on transplantation experiments, the inhibition gradient in the aberrant is steeper and higher near the head than that in the normal. Also, the amount of inhibition transmitted by the aberrant head is higher. Both epithelial cells and nerve cells have been implicated in the patterning process of hydra. The cell types involved in the altered inhibition properties of the aberrant were determined by making chimeras consisting of epithelial cells from one strain and nerve cells from the other. Experiments with these chimeras demonstrated that the epithelial cells were responsible for the altered inhibition gradient of the aberrant. In contrast, both the epithelial cells and the nerve cells were involved in the higher amount of inhibition transmitted by the aberrant head. Thus, both cell types are involved in this aspect of patterning.     

Characterization of interstitial stem cells in hydra by cloning.

A procedure has been developed for cloning interstitial stem cells from hydra. Clones are prepared by introducing small numbers of viable cells into aggregates of nitrogen mustard-inactivated host tissue. Clones derived from added stem cells are identified after 1–2 weeks of growth by staining with toluidine blue. The incidence of clones increases with increasing input of viable cells according to one-hit Poisson statistics, indicating that clones arise from single cells. After correction for cell losses in the procedure, about 1.2% of the input cells are found to form clones. This compares with estimates from in vivo experiments of about 4% stem cells in whole hydra [David, C. N., and Gierer, A. (1974). Cell cycle kinetics and development of Hydra attenuata. III. Nerve and nematocyte differentiation. J. Cell Sci.16, 359–375.]Differentiation of nematocytes and nerve cells in clones was analyzed by labeling precursors with [³H]thymidine and scoring labeled nerves and nematocytes 2 days later. Nine clones examined in this way contained both differentiated nerve cells and nematocytes, demonstrating that the interstitial stem cell is multipotent. This result suggests that the observed localization of nerve and nematocyte differentiation in whole hydra probably occurs at the level of stemcell determination. The observation that differentiated cells occur very early in clone development suggests that a stem cell's decision to proliferate or differentiate is regulated by shortrange feedback signals which are already saturated in young clones.     

Chemoreception in hydra: specific binding of glutathione to a membrane fraction.

Specific binding of reduced [35S]glutathione (GSH) was measured using a crude membrane fraction of Hydra vulgaris (attenuata). The specific binding shows both rapid displaceable and nondisplaceable components. Rapid displaceable binding accounted for 20% of the total specific binding. Data from saturation binding experiments indicates half maximal total specific binding occurs at 2 microM GSH which is similar to reported EC50 values from behavioral experiments. Calcium is required for displaceable binding of GSH to the putative receptor. Oxidized glutathione (GSSG), an antagonist of the GSH-activated feeding response, and S-methylglutathione (GSM), an agonist of the feeding response, inhibit the binding of radiolabeled GSH to the putative receptor. Glutamate, a putative competitive antagonist of the GSH-activated feeding response in hydra, does not inhibit the specific binding of radiolabeled GSH to the receptor and must therefore block the feeding response by a mechanism other than competitive inhibition.     

The Establishment of the Hydra-Chlorella Symbiosis: Recognition of Potential Algal Symbionts

The epithelial cells lining the gastric cavity of the freshwater hydra, Hydra viridis, harbor unicellular algal symbionts of the genus Cblorella. It has long been known that these hydra cells can readily phagocytose algal cells and will sequester those algae that have the potential to form a symbiotic association. In this paper the evidence is discussed for when and how recognition of potential symbionts by hydra cells occurs, i.e. during phagocytosis or during the subsequent intracellular events leading to sequestration of algal symbionts.     

Transplantation stimulates interstitial cell migration in hydra

Migration of interstitial cells and nerve cell precursors was analyzed in Hydra magnipapillata and Hydra vulgaris (formerly Hydra attenuata). Axial grafts were made between [3H]thymidine-labeled donor and unlabeled host tissue. Migration of labeled cells into the unlabeled half was followed for 4 days. The results indicate that the rate of migration was initially high and then slowed on Days 2-4. Regrafting fresh donor tissue on Days 2-4 maintained high levels of migration. Thus, migration appears to be stimulated by the grafting procedure itself.     

Localization of dopamine in the freshwater hydrozoanHydra attenuata

Summary High performance liquid chromatography (HPLC), with electrochemical detection, is an analytical method sensitive enough to permit quantification of dopamine, dihydroxyphenylalanine (DOPA) and 5-S-cysteinyl DOPA in single or hemisected specimens ofHydra attenuata. Dopamine and 5-S-cysteinylDOPA appear to be the quantitatively predominant catechol compounds inH. attenuata, whereas DOPA is present in minor amounts. The presence of DOPA and 5-S-cysteinylDOPA, and the quantitative correlation between dopamine and these compounds in many specimens, suggests that dopamine inH. attenuata, as in higher animals, is formed through decarboxylation of DOPA. Contrary to the dopaminergic nerves in higher animals, DOPA inHydra seems to be oxidized and 5-S-cysteinyl DOPA is formed as a by-product. The oxidation of DOPA indicates that the hydroxylation of tyrosine into DOPA in the tissues ofH. attenuata is mediated by a tyrosinase rather than a tyrosine hydroxylase. Immunocytochemical methods demonstrate a highly variable distribution of dopamine in the tissues of different specimens ofH. attenuata. Dopamine immunoreactivity is confined to ectodermal tissue and can be found in several different cell types including nerve cells, battery cells, nematocytes, epithelial cells and interstitial undifferentiated cells. The large amounts of dopamine found in some specimens ofH. attenuata indicate some biological function, although its sporadic occurrence in neurites makes it less plausible as a generally utilized neurotransmitter in this animal.     

Mitochondrial DNA of Hydra attenuata (Cnidaria): A Sequence That Includes an End of One Linear Molecule and the Genes for l-rRNA, tRNAf-Met, tRNATrp, COII, and ATPase8

The 3231-nucleotide-pair (ntp) sequence of one end of one of the two linear mitochondrial (mt) DNA molecules of Hydra attenuata (phylum Cnidaria, class Hydrozoa, order Anthomedusae) has been determined. This segment contains complete genes for tRNA^f-Met, l-rRNA, tRNA^Trp, subunit 2 of cytochrome c oxidase (COII), subunit 8 of ATP synthetase (ATPase8), and the 5′ 136 ntp of ATPase6. These genes are arranged in the order given and are transcribed from the same strand of the molecule. As in two other cnidarians, the hexacorallian anthozoan Metridium senile and the octocorallian anthozoan Sarcophyton glaucum, the mt-genetic code of H. attenuata is near standard. The only modification appears to be that TGA specifies tryptophan rather than termination. Also as in M. senile and S. glaucum, the encoded H. attenuata mt-tRNA^f-Met has primary and secondary structural features resembling those of Escherichia coli initiator tRNA^t-Met. As the encoded mt-tRNA^Trp cannot be folded into a totally orthodox secondary structure, two alternative forms are suggested. The encoded H. attenuata mt-l-rRNA is 1738 nt, which is 451 nt shorter than the M. senile mt-l-rRNA. Comparisons of secondary structure models of these two mt-l-rRNAs indicate that most of the size difference results from loss of nucleotides in the H. attenuata molecule at a minimum of 46 locations, which includes elimination of six distinct helical elements. Received: 9 March 2000 / Accepted: 24 July 2000     

Bud formation in the scyphozoan Cassiopea andromeda: epithelial dynamics and fate map

Cassiopea andromeda scyphistomae reproduce asexually by forming spindle shaped buds which, after detachment, metamorphose into polyps. Parent polyps appear to contribute to the buds' ecto- and endodermal epithelial cells, septal muscle cells, nematocytes and some zooxanthellae. Herein we describe bud morphogenesis, define 5 bud stages, and investigate the recruitment of bud ectoderm. India ink vital marking experiments reveal permanent apicobasal displacement of ectoderm. Labelled polyp cells are displaced towards and incorporated into the emerging bud. Ectoderm is recruited from all angular positions and cells labelled at increasing distances from the bud center are traced at increasingly more proximal positions on the buds. Unlike in Hydra attenuata, the recruitment area appears to be asymmetric since the zone contributing ectoderm from below is smaller than the zones above and lateral to the buds.     

Nucleotide sequence of an actin-encoding gene from Hydra attenuata: structural characteristics and evolutionary implications

We have determined the complete nucleotide sequence of an actin-encoding gene from Hydra attenuata as well as partial sequences of cDNA clones from two additional actin-encoding genes. The gene from the genomic clone contains a single intron, and has promoter and polyadenylation signals similar to those found in other species. The hydra genome has a very A + T-rich base composition (71%). This is reflected in the codon usage of the actin-encoding genes, which is strongly biased towards codons having A or T in the third position. The hydra actin-encoding gene family consists of three or more transcribed genes, two of which are very closely related to each other and probably arose by a recent gene duplication. Hydra actin, like other invertebrate actins, is more similar to the non-muscle isotypes of vertebrates than to the vertebrate muscle actins. Hydra actin is more similar to animal actins than to those of plants or fungi, which is consistent with the view that all metazoans arose from a single protist ancestor.