__NOTOC__ ''Euprymna scolopes'', also known as the Hawaiian bobtail squid, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

bobtail squid Bobtail squid (order Sepiolida) are a group of cephalopods closely related to cuttlefish. Bobtail squid tend to have a rounder mantle than cuttlefish and have no cuttlebone. They have eight suckered arms and two tentacles and are generally qui ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Sepiolidae Sepiolidae is a family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its me ...

native to the central

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

, where it occurs in shallow coastal waters off the

Hawaiian Islands The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost Kur ...

and

Midway Island Midway Atoll (colloquial: Midway Islands; haw, Kauihelani, translation=the backbone of heaven; haw, Pihemanu, translation=the loud din of birds, label=none) is a atoll in the North Pacific Ocean. Midway Atoll is an insular area of the Unit ...

.Reid, A. & P. Jereb 2005. Family Sepiolidae. ''In:'' P. Jereb & C.F.E. Roper, eds. ''Cephalopods of the world. An annotated and illustrated catalogue of species known to date. Volume 1. Chambered nautiluses and sepioids (Nautilidae, Sepiidae, Sepiolidae, Sepiadariidae, Idiosepiidae and Spirulidae)''. FAO Species Catalogue for Fishery Purposes. No. 4, Vol. 1. Rome, FAO. pp. 153–203. The type specimen was collected off the Hawaiian Islands and is deposited at the

National Museum of Natural History The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. In 2021, with 7 ...

Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...

''Euprymna scolopes'' grows to in

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

length. Hatchlings weigh and mature in 80 days. Adults weigh up to . In the wild, ''E. scolopes'' feeds on species of

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...

, including ''

Halocaridina rubra ''Halocaridina rubra'', the Hawaiian red shrimp or volcano shrimp is a small red shrimp of the family Atyidae, with the common Hawaiian name (meaning "red shrimp"). Description and distribution It is a small red shrimp, rarely longer than in ...

'', ''

Palaemon debilis ''Palaemon debilis'' is a species of shrimp of the family Palaemonidae Palaemonidae is a family of shrimp in the order Decapoda. Many species are carnivores that eat small invertebrates, and can be found in any aquatic habitat except the dee ...

'', and ''

Palaemon pacificus ''Palaemon pacificus'' is a species of shrimp of the family (biology), family Palaemonidae. References

Palaemonidae Crustaceans described in 1860 {{Caridea-stub ...

''. In the laboratory, ''E. scolopes'' has been reared on a varied diet of animals, including

mysid Mysida is an order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch or "marsupium" in females. The fact that the larvae are reared in thi ...

s ('' Anisomysis'' sp.),

brine shrimp ''Artemia'' is a genus of aquatic crustaceans also known as brine shrimp. It is the only genus in the family Artemiidae. The first historical record of the existence of ''Artemia'' dates back to the first half of the 10th century AD from Urmia La ...

(''

Artemia salina ''Artemia salina'' is a species of brine shrimp – aquatic crustaceans that are more closely related to ''Triops'' and cladocerans than to true shrimp. It belongs to a lineage that does not appear to have changed much in . ''A. salina'' is nati ...

''),

mosquitofish The western Mosquitofish (''Gambusia affinis'') is a North American freshwater fish, also known commonly, if ambiguously, as simply Mosquitofish or by its generic name, ''Gambusia'', or by the common name gambezi. Its sister species, the easte ...

(''

Gambusia affinis The western Mosquitofish (''Gambusia affinis'') is a North American freshwater fish, also known commonly, if ambiguously, as simply Mosquitofish or by its genus, generic name, ''Gambusia'', or by the common name gambezi. Its sister species, th ...

''),

prawn Prawn is a common name for small aquatic crustaceans with an exoskeleton and ten legs (which is a member of the order decapoda), some of which can be eaten. The term "prawn"Mortenson, Philip B (2010''This is not a weasel: a close look at nature ...

s (''

Leander debilis Leander is one of the protagonists in the story of Hero and Leander in Greek mythology. Leander may also refer to: People * Leander (given name) * Leander (surname) Places * Leander, Kentucky, United States, an unincorporated community * Lea ...

''), and

octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...

es (''

Octopus cyanea ''Octopus cyanea'', also known as the big blue octopus or day octopus, is an octopus in the family Octopodidae. It occurs in both the Pacific and Indian Oceans, from Hawaii to the eastern coast of Africa.Norman, M.D. 2000. ''Cephalopods: A World ...

''). The

Hawaiian monk seal The Hawaiian monk seal (''Neomonachus schauinslandi'') is an endangered species of earless seal in the family Phocidae that is endemic to the Hawaiian Islands. The Hawaiian monk seal is one of two extant monk seal species; the other is the Med ...

(''Monachus schauinslandi'') preys on ''E. scolopes'' in northwestern Hawaiian waters. On June 3, 2021,

SpaceX CRS-22 SpaceX CRS-22, also known as SpX-22, was a Commercial Resupply Services (CRS) mission to the International Space Station (ISS) that launched at 17:29:15 UTC on 3 June 2021. The mission is contracted by NASA and is flown by SpaceX using a Carg ...

launched ''E. scolopes,'' along with

tardigrade Tardigrades (), known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär ...

s, to the

International Space Station The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...

. The squid were launched as hatchlings and will be studied to see if they can incorporate their symbiotic bacteria into their light organ while in space.

Symbiosis

''Euprymna scolopes'' lives in a

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

relationship with the

bioluminescent Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorganisms including ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

Aliivibrio fischeri ''Aliivibrio fischeri'' (also called ''Vibrio fischeri'') is a Gram-negative, rod-shaped bacterium found globally in marine environments. This species has bioluminescent properties, and is found predominantly in symbiosis with various marine an ...

'', which inhabits a special light organ in the squid's mantle. The bacteria are fed a

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...

and

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

solution by the squid and in return hide the squid's silhouette when viewed from below by matching the amount of light hitting the top of the mantle (

counter-illumination Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength. Marine animals of ...

).Young, R.E. & C.F. Roper 1976. Bioluminescent countershading in midwater animals: evidence from living squid. ''Science'' 191(4231): 1046–1048. ''E. scolopes'' serves as a

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

for animal-bacterial symbiosis and its relationship with ''A. fischeri'' has been carefully studied.

Acquisition

The bioluminescent bacterium, ''A. fischeri'', is horizontally transmitted throughout the ''E. scolopes'' population. Hatchlings lack these necessary bacteria and must carefully select for them in a marine world saturated with other microorganisms.Effects of colonization, luminescence, and autoinducer on host transcription during development of the squid-vibrio association.''

Proceedings of the National Academy of Sciences of the United States of America ''Proceedings of the National Academy of Sciences of the United States of America'' (often abbreviated ''PNAS'' or ''PNAS USA'') is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Scien ...

'' 105(32): 11323-11328. To effectively capture these cells, ''E. scolopes'' secretes

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

in response to

peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ...

(a major

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

component of

).The evolutionary ecology of a sepiolid squid-''Aliivibrio'' association: from cell to environment. ''

Vie et Milieu Vie (IPA: /'vi.e/), is a district (or ''quarter''), of Oradea, a city in Bihor, Romania. The name means ''vineyard'' in Romanian. Geography Vie is situated in the hills overlooking Oradea, in the northern part of the town. It spans quite a lar ...

58(2): 175-184. The mucus inundates the

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

ted fields in the immediate area around the six pores of the light organ and captures a large variety of bacteria. However, by some unknown mechanism, ''A. fischeri'' is able to outcompete other bacteria in the mucus. As ''A. fischeri'' cells aggregate in the mucus, they must use their

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

to migrate through the

pore Pore may refer to: Biology Animal biology and microbiology * Sweat pore, an anatomical structure of the skin of humans (and other mammals) used for secretion of sweat * Hair follicle, an anatomical structure of the skin of humans (and other m ...

s and down into the ciliated ducts of the light organ and endure another barrage of host factors meant to ensure only ''A. fischeri'' colonization. Besides the relentless host-derived current that forces

motility Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

-challenged bacteria out of the pores, a number of reactive oxygen species makes the environment unbearable. Squid halide peroxidase is the main enzyme responsible for crafting this microbiocidal environment, using

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

as a substrate, but ''A. fischeri'' has evolved a brilliant counterattack. ''A. fischeri'' possesses a periplasmic

catalase Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting t ...

that captures hydrogen peroxide before it can be used by the squid halide peroxidase, thus inhibiting the enzyme indirectly. Once through these ciliated ducts, ''A. fischeri'' cells swim on towards the antechamber, a large

epithelial Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

-lined space, and colonize the narrow epithelial crypts. The bacteria thrive on the host-derived amino acids and sugars in the

antechamber A vestibule (also anteroom, antechamber, or foyer) is a small room leading into a larger space such as a lobby, entrance hall or passage, for the purpose of waiting, withholding the larger space view, reducing heat loss, providing storage space ...

and quickly fill the crypt spaces within 10 to 12 hours after hatching.An exclusive contract: Specificity in the ''Aliivibrio fischeri'' ''Euprymna scolopes'' partnership. ''

Journal of Bacteriology The ''Journal of Bacteriology'' is a biweekly peer-reviewed scientific journal established in 1916. It is published by the American Society for Microbiology and the editor in chief is George A. O'Toole (Dartmouth College). The journal is delayed o ...

'' 182(7): 1779-1787.

Ongoing relationship

Every second, a juvenile squid ventilates about of ambient

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...

through its mantle cavity. Only a single ''A. fischeri'' cell, one/1-millionth of the total volume, is present with each ventilation. The increased amino acids and sugars feed the

metabolically Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

demanding

bioluminescence Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...

of the ''A. fischeri'', and in 12 hours, the bioluminescence peaks and the juvenile squid is able to counterilluminate less than a day after hatching. Bioluminescence demands a substantial amount of energy from a bacterial cell. It is estimated to demand 20% of a cell’s metabolic potential. Nonluminescent strains of ''A. fischeri'' would have a definite competitive advantage over the luminescent wild-type, however nonluminescent mutants are never found in the light organ of the ''E. scolopes''. In fact, experimental procedures have shown that removing the

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

s responsible for light production in ''A. fischeri'' drastically reduces colonization efficiency. Luminescent cells, with functioning

luciferase Luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words ''luciferin'' and ''luciferase'', ...

, may have a higher affinity for

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

than for

peroxidases Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides. Functionality Peroxidases typically ca ...

, thereby negating the toxic effects of the peroxidases.The evolution of bioluminescent oxygen consumption as an ancient oxygen detoxification mechanism.''

Journal of Molecular Evolution The ''Journal of Molecular Evolution'' is a monthly peer-reviewed scientific journal that covers molecular evolution. It is published by Springer Science+Business Media and was established in 1971. The founding editor was Emile Zuckerkandl, who re ...

'' 52(4): 321-332. For this reason, bioluminescence is thought to have evolved as an ancient oxygen detoxification mechanism in bacteria.

Venting

Despite all the effort that goes into obtaining luminescent ''A. fischeri'', the host squid jettisons most of the cells daily. This process, known as “venting”, is responsible for the disposal of up to 95% of ''A. fischeri'' in the light organ every morning at dawn.Breaking the language barrier: experimental evolution of non-native Aliivibrio fischeri in squid tailors luminescence to the host. ''

Symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

'' 51(1): 85-96. The bacteria gain no benefit from this behavior and the upside for the squid itself is not clearly understood. One reasonable explanation points to the large energy expenditure in maintaining a colony of bioluminescent bacteria.Counterillumination in the Hawaiian bobtail squid, ''Euprymna scolopes'' Berry (Mollusca : Cephalopoda). ''

Marine Biology Marine biology is the scientific study of the biology of marine life, organisms in the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies s ...

'' 144(6): 1151-1155. During the day when the squid are inactive and hidden, bioluminescence is unnecessary, and expelling the ''A. fischeri'' conserves energy. Another, more evolutionarily important reason may be that daily venting ensures selection for ''A. fischeri'' that have evolved specificity for a particular host, but can survive outside of the light organ. Since ''A. fischeri'' is transmitted horizontally in ''E. scolopes'', maintaining a stable population of them in the open ocean is essential in supplying future generations of squid with functioning light organs.

Light organ

The light organ has an electrical response when stimulated by light, which suggests the organ functions as a photoreceptor that enables the host squid to respond to ''A. fischeris luminescence. Extraocular

vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features o ...

collaborate with the eyes to monitor the down-welling light and light created from counterillumination, so as the squid moves to various depths, it can maintain the proper level of output light. Acting on this information, the squid can then adjust the intensity of the

by modifying the

ink sac An ink sac is an anatomical feature that is found in many cephalopod mollusks used to produce the defensive cephalopod ink. With the exception of nocturnal and very deep water cephalopods, all Coleoidea (squid, octopus and cuttlefish) which dwell ...

, which functions as a diaphragm around the light organ. Furthermore, the light organ contains a network of unique reflector and lens tissues that help reflect and focus the light ventrally through the

. The light organ of

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

nic and juvenile squids has a striking anatomical similarity to an eye and

expresses Expression may refer to: Linguistics * Expression (linguistics), a word, phrase, or sentence * Fixed expression, a form of words with a specific meaning * Idiom, a type of fixed expression * Metaphorical expression, a particular word, phrase, o ...

several genes similar to those involved in eye development in mammalian embryos (e.g. '' eya'', '' dac'') which indicate that squid eyes and squid light organs may be formed using the same

developmental Development of the human body is the process of growth to maturity. The process begins with fertilization, where an egg released from the ovary of a female is penetrated by a sperm cell from a male. The resulting zygote develops through mitosi ...

"toolkit". As the down-welling light increases or decreases, the squid is able to adjust luminescence accordingly, even over multiple cycles of light intensity.

References

External links

The Light-Organ Symbiosis of ''Vibrio fischeri'' and the Hawaiian squid, ''Euprymna scolopes''

Mutualism of the Month: Hawai‘ian bobtail squid
{{Taxonbar, from=Q150870 Bobtail squid Bioluminescent molluscs Molluscs of Hawaii Endemic fauna of Hawaii Molluscs described in 1913 Symbiosis Taxa named by Samuel Stillman Berry