Japetella heathi

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Japetella heathi
Systematics
Subclass : Octopus (coleoidea)
Superordinate : Eight-armed squid (Vampyropoda)
Order : Octopus (octopoda)
Family : Gelatinous (Bolitaenidae)
Genre : Japetella
Type : Japetella heathi
Scientific name
Japetella heathi
( Berry , 1911)

Japetella heathi is a species of octopus within the eight-armed squid (Vampyropoda). The other species of the genus Japetella described is Japetella diaphana Hoyle , 1885. Japetella heathi is characterized by its small body size in relation to its relative, short arms and its camouflage dynamics. The latter occurs in a number of animal species and its basic principles and a. taken upin bionic approaches.

anatomy

The bilaterally symmetrical dwarf octopuses reach an average total length of 8–12 cm (max. Mantle length: 8 cm). J. heathi , because she belongs to the Bolitaenidengruppe, has comparatively short tentacles and large, laterally located short-stemmed eyes. The molluscs have neither an endo- nor an exoskeleton . The head is surrounded by a protective cartilage capsule.

In young animals, the eyes border directly on the brain, in adult specimens, however, they are a little further away and shifted outwards. The tentacles each have a single row of suction cups ; in male specimens these enlarge on the third left tentacle during the mating season. It is not known whether this is used in Japetella heathi as in other bolitaenids for hectocotylization (modification of the arm tip; serves to transport spermatophores from Needham's pocket (= storage bag for spermatophores) into the female's mantle cavity ). The animals are of separate sex . Breathing works through two gills located in the mantle cavity , the absorption of messenger substances via the olfactory pit behind the eyes, the Spengler organ in front of the mantle cavity or chemoreceptors of the suction cups. The circulatory system of animals is as closed at all cephalopods. The long axis of the digestive tract is parallel to the body axis; the stomach lies behind it. The radula is laterally covered with molar teeth (= ctenoglossan).

distribution

Geographical distribution

Japetella heathi is only distributed in the northern hemisphere and occurs there in subtropical and nemoral zones of the eastern Pacific and the Atlantic. The species lives largely pelagic , i.e. free-swimming in the coastal areas of the oceans. It may move as far as the boreal coasts of North America. Their natural ambient temperature is 4–5 ° C due to the relatively great depth of their habitat .

Vertical spread

Like all cephalopods, Japetella heathi is an animal that occurs exclusively in the sea. It can be found in meso- to basypelagial zones, i.e. at depths of up to 1500 meters on the open sea, where a strong ontogenetic change in terms of vertical distribution is noticeable. The young animals (under 20 mm mantle length) prefer to live at depths of 200–700 meters below the surface, fully grown specimens stay in daylight below mostly over 800 meters below sea level.

Hunting behavior and diet

The octopuses move using the recoil principle and feed carnivorously ; They catch their food with the sessile suction cups on their tentacles. Due to its small size, Japetella heathi feeds mainly on small fish, fish larvae, free-swimming shrimp , other mollusks and plankton . Octopods are - for humans - slightly to negligibly toxic , but with the poison from their salivary glands they paralyze their prey so that they can hold and chop it up.

Courtship behavior, reproduction, and life cycle

The adult Japetella heathi lives solitary and probably only reproduces once in their life. The mating time is an exceptional situation with regard to the territory of the animals, as the female (and probably also the male) octopuses go to lightless depths of up to 1500 meters.

It is currently believed that several key stimuli play a role in fertilization in that the male first secretes a secretion from his posterior salivary gland that acts like a pheromone on female Japetella heathi . In a second step, attracted by the messenger substance, the latter approaches to a distance that it estimates with sufficient certainty and signals its position to the male by means of its luminous organ (photophore). To attract males, fertile females form a transluminescent ring around the mouth opening as a photophore, which shines through the darkness as bioluminescence . The body's internal luciferin- luciferase systems serve as producers . Neither the olfactory note nor the visual stimulus are completely intrinsic to species , which means that predators may not be able to prevent them from becoming aware.

After mating, the pregnant female goes back up to deeper oxygen levels of up to 500 meters, where she does intensive brood care . The eggs of the cuttlefish are connected to each other by jelly-like stalks and thus form a grape-like mass that the mother animal holds with its suction cups between the four pairs of arms and near the mouth and wags fresh water currents towards them. At the beginning of embryonic development , a discoid furrow occurs , a germinal disc that rests on the yolk as a cell cap and then grows around it as a yolk sac during gastrulation ( epibolism ). The UV radiation in this environment is just so low that it is difficult to see the female while breeding. If it were to climb even higher, the environment would already be too bright. Due to the cold environment, the eggs take several months to hatch, during which the animal foregoes food and makes its energy reserves available to the embryos . It usually dies from exhaustion or is eaten shortly after the offspring hatch. So while brood care is intensive, there is no subsequent brood bond.

Newly hatched Japetella heathi have a coat length of about 2-3 mm, which corresponds to the size of the eggs. After birth, the young Octobrachia either climb by themselves to higher, more nutritious areas of 200-300 m or are transported there by the mother shortly before. They stay there until they reach a certain size (7–20 mm).

Juvenile Japetella heathi have a particularly high mortality rate . In the 1980s there was a debate in research about the assumption that the juveniles rise in large numbers to within diving range of seabirds , since undigested remains of gelatinous deep-sea cephalopods were found in them. On the one hand, this theory applies because night-hunting albatrosses feed on squid when they visit the surface zones. Another explanation for this can be found with regard to the course of the maritime food chain : some tuna species such as the bigeye tuna hunt in mesopelagial zones and thus also after Japetella . The animals can not break down the octopods' radula and mandibles, which contain chitin . Albatrosses or petrels often fish in the wake of tuna longliners that fish from the deep sea and wash off offal and fish waste back into the sea after catching them. In this way, parts of cephalopods are often so well preserved for a long time that their origin can be precisely determined down to the family taxon. As they grow up, the young gradually penetrate deeper, mesopelagial and finally, for renewed mating, basypelagial zones. Japetella heathi is therefore one of the aquatic species that practice vertical migration .

Camouflage behavior

Most of the creatures in the deep sea are forced to use camouflage strategies and for this purpose have developed different methods of optical adaptation to the background. Some cephalopod species living in coral reefs can change not only color but also skin texture.

J. heathi counter potential dangers with sudden expansion and contraction of their chromatophores (pigment-containing cells) in the epithelium and connective tissue of the coat and arms. By membrane-internal kinesin -Movement (transport molecule), the pigments are either concentrated on one point, resulting in white black-to-point staining in light irradiation or melanins and red pigments are along the microtubules (part of the cytoskeleton with rail feature) in the melanocytes distributed and the skin darkens.

The natural habitat of the Bolitaeniden extends from those sea depths in which there is still diffuse light during the day to deep-sea zones just under a kilometer below the surface. At these depths, bioluminescence , usually used for hunting, is the only source of light. Depending on the distance from the sea level, the color of the octopus also changes. While they appear whitish-transparent in waters closer to the surface and are hardly visible, in the lightless depths they camouflage themselves with dark brown, black or red spots. Predators such as the lantern fish use bacteria to send symbiosis of light into the darkness to search for prey.

Within the mollusks, cephalopods have the most highly developed nervous system with sensory praise and a multilayered cortex . As soon as the dwarf octopuses perceive the bioluminescent light of a predator with their everted lens eyes and skin receptors, they suddenly change their color. They can thus cognitively control their pigmentation. A change in a fraction of a second is possible because the neurons are very dense in their skin and the chromatophores are also present in an expandable triple layer.

Due to their habitat, J. heathi have two types of predators :

Threat in transparent mode

The first category is made up of deep-sea predators such as ghost fish , who can turn their eyes towards the surface and look out for dark silhouettes of potential prey against the twilight. Some sea creatures counteract this by bioluminescing themselves on their belly, i.e. H. imitate the faint daylight from above. In J. heathi it is mainly the young animals whose chromatophore layers are less developed than the adult animals, which is why they are much more transparent and therefore remain above the sea floor. At the same time, less light-producing fish move around in these latitudes, which improves their chances of survival at night.

The octopuses appear almost transparent to the light of the surface, only the eyes and intestines are visible. Iridophores (whitish / silvery shimmering cells, store guanine platelets) are also embedded in the outer tissue layers of the dorsal arms and head . This is an additional protection in the transparent state, so that light not only falls through the body, but is also amplified. With sexual maturity, the iridescent properties of the digestive tract and eyes decline and the density of chromatophores increases.

Only in the course of growth, as soon as the pigment cells are fully developed, does Japetella heathi move into deeper, lightless areas.

Threat in aphotic depths

In the lightless deep sea, however, the transparent camouflage is counterproductive, as predators of the second category use bioluminescence to search for food in these zones . In its transparent state, Japetella heathi not only reflects fluorescence emissions, which were used in scientific experiments due to the similarity with the wavelength range of bioluminescence, but also reproduces this light twice as strongly as pigmented tissue. The transparent fabric layers do not provide sufficient camouflage. As soon as the animals are hit by the light, it is scattered inside the body and thus makes the entire animal visible. The reflection that the predator can perceive would therefore be a lot lighter than the background and would reveal the precise position and silhouette of the octopus.

Therefore, the spots of Japetella heathi can take on a reddish-brown color and expand in fractions of a second. Sarah Zylinski, scientist at Duke University in the USA, compared the effect that a bioluminescent light would have on purely transparent living beings in an interview with the "beam of a flashlight that hits a window glass at night" - the animals would be a species Create halo around you. Due to the natural “ invisibility ” cap, however, they no longer stand out from the dark background within seconds. The reason for this: bioluminescent light in the blue-green spectrum (450–500 nm) is the only light source that the eyes of deep-sea species can clearly perceive. It is precisely these rays of light that are largely absorbed by red surfaces.

In summary, it can be said that in higher mesopelagial zones most living things are transparent, while in lightless zones almost all taxa can camouflage themselves with red or black spots. The trigger here is an interspecific key stimulus (light serves as a key stimulus ), since the information gain between the hunter and the prey only takes place on the recipient side, i.e. the prey. Which of the two strategies is appropriate cannot, however, be determined solely on the basis of the depth value, but also depends on cloud cover, time of day, air and water cloudiness.

Zylinski experiments

The research project of an American team of ecologists led by Sarah Zylinski unearthed an eight-centimeter-long Japatella heathi and a thirteen-centimeter-long squid of the species Onychoteuthis banksii in the Atacama Trench and 2011 in the Gulf of California . The animals were caught at depths between 100 and 1000 meters. The deep-sea nets used had to be brought to the surface very slowly, as is customary on such journeys, in order not to expose the living beings to too abrupt light, temperature and pressure shock. Then the camouflage behavior of the dwarf octopus was experimentally researched by observing their reaction to visual and tactile stimuli . Young specimens of Japetella heathi in the transparent state were tested by irradiating them with bluish light (450 nm peak emission ) under subdued room light from a xenon lamp .

The only observable reaction of the animals to movement of objects above the water surface of their tank was that they followed the objects with their eyes. Also when using looming (method of optical illusion; objects are projected onto the retina of the test object and rapidly enlarged, creating the impression of approaching this object and mostly physical reactions; see English to loom - "to approach" , "emerge") the result was the same. When a tentacle was touched with a blunt needle for three seconds, which triggered increased stress, the cephalopods discolored all over their bodies, moved away from the needle and at the same time pulled their heads deeper into the mantle cavity.

The cephalopods were then irradiated every five seconds with bluish light from fluorescent- coated LED lamps, which is similar to the primary and secondary glow of their predators in the deep sea. The two specimens reacted to this stimulus with immediate metamorphosis: their skin turned dark and as soon as the cone of light left it - transparent again (reversible expansion of the chromatophores). This effect increased with each irradiation unit and finally led, like the tactile stimulus, to an evasive reaction (drawing of the head into the jacket). The pigment cells of the Japetella heathi turned reddish brown, those of the squid turned black. If the irradiation was continued after the maximum expansion of the chromatophores had been reached, this would lead to a subsequent retraction into the transparent state and any further irradiation no longer led to the discoloration.

In the tested Onychoteuthis banksii, the pigmentation did not disappear after some time as in Japetella heathi , although both species repeatedly tried to swim away from the light source.

Pigmented fabrics reflect a lot of light of longer wavelengths (500–700 nm), but overall far less than transparent ones. According to the measurement results, these values ​​were generally below 20% for the Bolitaenids for light of all wavelengths and 5–10% or below in the blue-green range, which is relevant for visibility in the deep sea. Animals exposed to reddish light (600 nm) did not react with significant changes or escape behavior. Japetella heathi "double" their chances of survival, since "the ability to switch rapidly between the two camouflage techniques optimizes camouflage".

swell

Individual evidence

  1. ↑ P. Bouchet, S. Gofas: Japetella Hoyle, 1885 , World Register of Marine Species 2013. Retrieved December 15, 2013.
  2. ↑ See The Taxonomicon , URL: http://taxonomicon.taxonomy.nl/TaxonTree.aspx?id=157776 as of January 25, 2013
  3. ^ Richard Young: The systematics and areal distribution of pelagic cephalopods from the seas off southern California. In: Smithson. Contrib. Zool. 97, 1972, pp. 1-159. After Johnson and Zylinski 2011.
  4. ^ A b Richard Young: Bolitaeninae Chun, 1911. Version July 7, 2013. The Tree of Life Web Project, http://tolweb.org/ Retrieved December 15, 2013.
  5. ↑ a b c d Richard Young: Japetella diaphana Hoyle 1885. Version dated January 8, 2013. The Tree of Life Web Project, http://tolweb.org/ Retrieved December 15, 2013. (This information refers explicitly to J. . diaphana , but also apply to J. heathi .)
  6. ↑ Distribution Map: Japetella . Ocean Biographic Information System Database. As of January 25, 2013.
  7. ^ Richard Young: Vertical distribution and photosensitive vesicles of pelagic cephalopods from Hawaiian waters . In: Fish. Bull. 76, 1978, pp. 583-615. according to Johnson / Zylinski (2011).
  8. ↑ Maggy Wassilieff, Steve O'Shea: Octopus and squid - Feeding and predation . In: Te Ara - the Encyclopedia of New Zealand Date: January 25, 2013.
  9. ↑ Grooving . Compact Lexicon of Biology, Spectrum Academic Publishing House. Retrieved January 25, 2013.
  10. ↑ Teodoro Vaske Jr .: Are deep-sea cephalopods really common preys for oceanic seabirds? In: Biota Neotropica. 11 (1), 2011, pp. 177-180. ( PDF, 189kB accessed on January 25, 2013).
  11. ↑ Clarke et al .: Cephalopod remains in regurgitation of the wandering albatross Diomedea exulans L. at South Georgia. In: Br. Antarct. Surv. Bull. 54, 1981, pp. 9-21. After Vaske Jr. 2011.
  12. ↑ Hanlon, Messenger: Cephalopod Behavior. 1996, Cambridge University Press, Cambridge. ISBN 0521645832 .
  13. ^ MJ McFall-Ngai: Crypsis in the pelagic environment . In: Am. Zool. 1990. After Johnson and Zylinski 2011.
  14. ^ S. Johnsen: Hidden in plain sight: the ecology and physiology of organismal transparency . In: Biol. Bull. 201, 2011, pp. 301-318. After Johnson and Zylinski 2011.
  15. ^ Richard Young: Oceanic bioluminescence: an overview of general functions . In: Bull. Mar. Sci. 33, 1983, pp. 829-845. After Johnson and Zylinski 2011.
  16. ^ Haddock, Moline, Case: Bioluminescence in the sea . In: Ann Rev Mar Sci. 2, 2010, pp. 443-493. After Johnson and Zylinski 2011.
  17. ^ P. Herring: The Biology of Deep Oceans . Oxford University Press, 2002. ISBN 0198549555 Adapted from Johnson and Zylinski 2011.
  18. ↑ Stephanie Tappas: Bam! Transparent octopus goes opaque in blink of an eye. In: NSNBC News Science Compartement, 2012. Retrieved January 25, 2013.

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