Hydra

When a hydra is well fed, a new bud can form every two days.[10] When conditions are harsh, often before winter or in poor feeding conditions, sexual reproduction occurs in some Hydra. Swellings in the body wall develop into either ovaries or testes. The testes release free-swimming gametes into the water, and these can fertilize the egg in the ovary of another individual. The fertilized eggs secrete a tough outer coating, and, as the adult dies (due to starvation or cold), these resting eggs fall to the bottom of the lake or pond to await better conditions, whereupon they hatch into nymph Hydra. Some Hydra species, like Hydra circumcincta and Hydra viridissima, are hermaphrodites[11] and may produce both testes and ovaries at the same time.

The feeding response in Hydra is induced by glutathione (specifically in the reduced state as GSH) released from damaged tissue of injured prey.[16] There are several methods conventionally used for quantification of the feeding response. In some, the duration for which the mouth remains open is measured.[17] Other methods rely on counting the number of Hydra among a small population showing the feeding response after addition of glutathione.[18] Recently, an assay for measuring the feeding response in hydra has been developed.[19] In this method, the linear two-dimensional distance between the tip of the tentacle and the mouth of hydra was shown to be a direct measure of the extent of the feeding response. This method has been validated using a starvation model, as starvation is known to cause enhancement of the Hydra feeding response.[19]

Hydra

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Hydra are capable of two types of DNA repair: nucleotide excision repair and base excision repair.[27] These repair pathways facilitate DNA replication by removing DNA damages. The identification of these pathways in hydra was based, in part, on the presence in the hydra genome of genes homologous to genes in other genetically well studied species that have been demonstrated to play key roles in these DNA repair pathways.[27]

An ortholog comparison analysis done within the last decade demonstrated that Hydra share a minimum of 6,071 genes with humans. Hydra is becoming an increasingly better model system as more genetic approaches become available.[5] Transgenic hydra have become attractive model organisms to study the evolution of immunity.[28] A draft of the genome of Hydra magnipapillata was reported in 2010.[29]

The genomes of cnidarians are usually less than 500 MB in size, as in the Hydra viridissima, which has a genome size of approximately 300 MB. In contrast, the genomes of brown hydras are approximately 1 GB in size. This is because the brown hydra genome is the result of an expansion event involving LINEs, a type of transposable elements, in particular, a single family of the CR1 class. This expansion is unique to this subgroup of the genus Hydra and is absent in the green hydra, which has a repeating landscape similar to other cnidarians. These genome characteristics make Hydra attractive for studies of transposon-driven speciations and genome expansions.[30]

Due to the simplicity of their life cycle when compared to other hydrozoans, hydras have lost many genes that correspond to cell types or metabolic pathways of which the ancestral function is still unknown.

Senescence, a deteriorative process that increases the probability of death of an organism with increasing chronological age, has been found in all metazoans where careful studies have been carried out. There has been much controversy, however, about the potential immortality of hydra, a solitary freshwater member of the phylum Cnidaria, one of the earliest diverging metazoan groups. Researchers have suggested that hydra is capable of escaping aging by constantly renewing the tissues of its body. But no data have been published to support this assertion. To test for the presence or absence of aging in hydra, mortality and reproductive rates for three hydra cohorts have been analyzed for a period of four years. The results provide no evidence for aging in hydra: mortality rates have remained extremely low and there are no apparent signs of decline in reproductive rates. Hydra may have indeed escaped senescence and may be potentially immortal.

We have already implemented the basic Hydra Head protocol as a proof of concept hydra-node. A developer preview will be ready by the time of the upcoming Cardano Summit. This will enable developers (or anyone interested) to run one or more hydra-nodes online, opening a Hydra Head with a limited number of participants, and feeding transactions to it. Users can expect to see a working prototype over a dedicated testnet, plus early benchmarking figures and documentation in this GitHub repository. There likely will not be any user-facing components (wallets, user interface, etc.) available just yet.

In the short term, we will keep developing the hydra-node and the Hydra Head protocol until it becomes a solid and stable foundation for the community (and us!) to build real-world applications. These new apps will benefit from fast settling and low-to-no-cost transactions. We are also actively developing other key features, including the support of multiple heads per node, persistence, and Head protocol extensions

Purina Pro Plan Veterinary Supplements Hydra Care is a nutrient-enriched water that promotes hydration in cats. It contains nutritional osmolytes, which aid in the absorption of water at a cellular level and helps cats get the hydration they need. The science behind our therapeutic products represents a collaboration between Purina nutritionists, researchers and veterinarians.Shown to increase total liquid intake *Promotes hydrationShown to decrease urine specific gravity *Easy to feedGreat taste* Compared to cats consuming only water in addition to dry feeding

To participate in the development of this specification, please join the Hydra W3C Community Group. If you have questions, want to suggest a feature, or raise an issue, please send a mail to the public-hydra@w3.org mailing list.

The first step when trying to access a Web API is to find an entry point. Typically, this is done by looking for documentation on the API publisher's homepage. Hydra enables the API's main entry point to be discovered automatically if the API publisher marks his responses with a special HTTP Link Header as defined in [[RFC5988]]. A Hydra client would look for a Link Header with a relation type (this is the IRI identifying the hydra:apiDocumentation property).

In many situations, it makes sense to expose resources that reference a set of somehow related resources. Results of a search query or entries of an address book are just two examples. To simplify such use cases, Hydra defines the two classes hydra:Collection and hydra:PartialCollectionView.

Since collections may become very large, Web APIs often chose to split a collection into multiple pages. In Hydra, that can be achieved with a hydra:PartialCollectionView. It describes a specific view on the collection which represents only a subset of the collection's members. A PartialCollectionView may contain links to the first, next, previous, and last PartialCollectionView which allows a client to find all members of a Collection.

An IriTemplate consists of a template literal and a set of mappings. Each IriTemplateMapping maps a variable used in the template to a property and may optionally specify whether that variable is required or not. The syntax of the template literal is specified by its datatype and defaults to the [[!RFC6570]] URI Template syntax, which can be explicitly indicated by hydra:Rfc6570Template.

Resources provided may have an additional hint pointing to an Error type like in the example above, but it is not mandatory to do so as all resources described with application/problem+json are considered hydra:Error.

Client can express its preferences through the Prefer HTTP header by pointing the preferred extensions via IRIs as on the example below. The client SHOULD use the Prefer HTTP header [[!RFC7240]] with the hydra.extension preference as an iri attribute having the IRI of the extension as value to hint the server about the extension it supports. Multiple preferences can be expressed by providing multiple Prefer header values.

They have been the many-headed creatures of myth and the arch-enemies of those doughty Agents of S.H.I.E.L.D. But real hydra, although they may not be much to look at, are far more interesting than either: immortality anyone? 2990b30de8