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

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Sepiolidae native to the central

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

, where it occurs in shallow coastal waters off the

Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...

and Midway Island.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 located at the

National Museum of Natural History The National Museum of Natural History (NMNH) 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. With 4.4 ...

Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...

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

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

, including '' Halocaridina rubra'', '' Palaemon debilis'', and '' Palaemon pacificus''. 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 or ''Sea-Monkeys, sea monkeys''. It is the only genus in the Family (biology), family Artemiidae. The first historical record of the existence of ''Artemia'' dates back to t ...

('' Artemia salina''), mosquitofish ('' Gambusia affinis''),

prawn Prawn is a common name for small aquatic crustaceans with an exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the intern ...

s ('' Leander debilis''), and

octopus An octopus (: octopuses or octopodes) 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, cuttlefish, and nautiloids. Like oth ...

es ('' Octopus cyanea''). The Hawaiian monk seal (''Monachus schauinslandi'') preys on ''E. scolopes'' in northwestern Hawaiian waters. On June 3, 2021, SpaceX CRS-22 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 . In 1776, th ...

s, to the

International Space Station The International Space Station (ISS) is a large space station that was Assembly of the International Space Station, assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United ...

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

Symbiosis

''Euprymna scolopes'' lives in a

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

relationship with the

bioluminescent Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms inc ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

'' Aliivibrio fischeri'', which inhabits a special light organ in the squid's mantle. To allow this symbiotic relationship, ''Crumbs'' protein must first induce

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

, which kills superficial epithelial tissue found in ''Euprymna scolopes.'' Unlike the superficial tissue, epithelial cells in deep invaginations of the internal part of the light organ, known as crypts, directly take in the bioluminescent ''Aliivibrio fischeri'' and do not undergo apoptosis. 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 Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...

and

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

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 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 workings of other organisms. Mo ...

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 Scie ...

'' 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 fluid, serous and muc ...

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 layer (sacculus) that surrounds the bacterial cytoplasmic membrane. The sugar component consists of alternating ...

(a major

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

component of

).The evolutionary ecology of a sepiolid squid-''Aliivibrio'' association: from cell to environment. '' Vie et Milieu 58(2): 175-184. '' The mucus inundates the

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

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 (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

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 ...

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 metabolism, metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components. Motility is observed in ...

-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 viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

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 ...

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 a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

-lined space, and colonize the narrow epithelial crypts. The bacteria thrive on the host-derived amino acids and sugars in the antechamber 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 A journal, from the Old French ''journal'' (meaning "daily"), may refer to: *Bullet journal, a method of personal organization *Diary, a record of personal secretive thoughts and as open book to personal therapy or used to feel connected to onesel ...

'' 182(7): 1779-1787.

Ongoing relationship

Every second, a juvenile squid ventilates about of ambient

seawater Seawater, or sea 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 approximat ...

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 ''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 cellular processes; the c ...

demanding

bioluminescence Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorgani ...

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 has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

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 a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

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, and should not be confused with other ...

, 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'' 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 that inhabit the sea. Given that in biology many scientific classification, phyla, family (biology), families and genera have some species that live in the sea and ...

'' 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 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 mantle. The light organ of

embryo An embryo ( ) is the initial stage of development for 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 sp ...

nic and juvenile squids has a striking anatomical similarity to an eye and expresses 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 "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
{{Authority control Bobtail squid Bioluminescent molluscs Molluscs of Hawaii Endemic fauna of Hawaii Cephalopods described in 1913 Symbiosis Taxa named by Samuel Stillman Berry Space-flown life