Triops longicaudatus
| Triops longicaudatus | ||||||||||||
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Triops longicaudatus |
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| Scientific name | ||||||||||||
| Triops longicaudatus | ||||||||||||
| ( LeConte , 1846) |
Triops longicaudatus is a representative of the back shell (Notostraca), a species-poor relic group of the gill pods with a special specialization in only temporarily water-bearing (ephemeral) waters,well-known from America. The species has been the only American representative of this group since Alan Longhurst's revision of the back scarf in 1955, until in 1997 Clay Sassaman and colleagues found out that the species name probably contains two crypto species. The secondspecies, separatedfrom Triops longicaudatus , wascalled Triops newberryi (according to an older description). In older adaptations under the species name Triops longicaudatus it is therefore unclear which of these species actually existed.
Besides Triops cancriformis , this species is one of the best-researched representatives of the genus Triops . Their diverse adaptations to a particularly dynamic habitat are remarkable - ephemeral small bodies of water such as puddles and meadow pools , which form in spring and dry out completely in the hot months. In addition to the brine shrimp of the genus Artemia , the animals have become popular under the colloquial name "Tadpole Shrimp" and are often offered in the form of their eggs and rearing kits. These eggs come predominantly from the species discussed here, which are bred for this in large numbers.
morphology
Triops has three eyes that are arranged in a triangle on the top of the head and gave the genus its name ("the three-eyed"). In addition to the two sessile complex eyes, each with around 250 ommatidia, there is the unpaired nauplius eye in the middle, a single eye that is not composed or faceted (ocellus).
As with all crustaceans, in Triops longicaudatus, the segments lying one behind the other, of which the body consists of an average of one to four centimeters long, are combined into functional units, the tagmata . On the upper side in the area of the Tagmata head ( cephalon ) and chest ( pereion or thorax ), the trunk is protected from the segment of the 2nd maxilla (which is not formed in this species) by a flat, shield-shaped carapace (back armor). The final tagma is the tubular abdomen ( abdomen ) with the furca , a forked appendix formed from two branches (rami) on the last abdominal segment ( telson ). The epithet “longicaudatus” (long-tailed) also refers to the Furca, which accounts for a large part of the total length .
On the underside of the body are the mouthparts on the head and on each of the 35 to 44 segments of the pereion a pair of leaf-shaped legs (leaf legs), between which a deep central food channel runs. These jointless sternum bones (pereiopods) fulfill various tasks: In addition to swimming, running and digging, they also serve to filter food particles and to breathe. Because they owe some of their strength to the turgor (hemolymph pressure), they are also known as turgor extremities. At the base of the abdomen there are 35 to 70 thin, hair-like appendages that support the leaf bones in locomotion and food transport. The two pairs of antennae are relatively small and hidden under the shield, instead the first pair of legs forms long extensions that are sensitive to taste and touch, but mainly serve for locomotion.
Nomenclature and systematics
The species was first scientifically described in 1848 by John Lawrence Le Conte as Apus longicaudatus . However, the name of the genus was recognized in 1909 by Ludwig Keilhack as the younger homonym of the bird genus Apus Scopoli , in 1777 and thus invalid . The generic name Triops Cabinet , previously taken as a synonym , became the replacement name in 1803 .
In the zoological system , the genera Triops and Lepidurus are assigned to the Triopsidae , the only family within the order of the Notostraca .
Geographical distribution
The animal geographical distribution area of this back saddle moth extends from southwestern Canada, from about the 50th northern latitude , south across parts of Central and South America. However, cancer also occurs in other parts of the world, such as Japan, the Galápagos Islands, and the West Indies . In the USA it is found mainly in desert and steppe areas and occurs in all states including Hawaii , with the exception of Alaska .
ecology
Habitat characteristics
The typical habitat is the warm, shallow small bodies of water filled with muddy alkaline water - ponds, floodpumps and puddles - as they can form in terrain depressions of different types and sizes (depressions and ditches, also in tire tracks). The "vernal pools" in the Sierra Nevada are a good example of this . They occur in spring after heavy seasonal rains or snowmelt, especially when rivers overflow their banks (“flash floods”). If the soil is suitable, the water does not seep away, but remains for a few months, often only weeks. All of these bodies of water are desiccation waters that only temporarily carry water. This forces Triops longicaudatus to grow and reproduce with great speed before all the water has disappeared.
Abiotic factors
Triops longicaudatus lives in small and very small bodies of water, in which the chemistry, temperature and oxygen content can change considerably during the day within a few hours, which is why the cancer shows a high tolerance to such fluctuations ( Euryökie ). Only in the first days of life are the nauplii relatively sensitive and losses can occur.
PH value
The cancer can exist within a pH range of 6.0 to 10.0, optimal is a value between pH 7.0 and 9.0. A fluctuation of up to two pH values, as can occur within a day / night rhythm, is tolerated without any problems.
Oxygen content
Triops longicaudatus has very low demands on the oxygen content and is content with a minimum of around one milligram of dissolved oxygen per liter (mg / l). But since the oxygen content does not fall below 2 mg / l even under the stagnant conditions in a desert pond heated by the sun, there is rarely a shortage of oxygen. In such a case, the crustacean swims on its back along the surface of the water (but it sometimes shows this behavior when searching for food), where the water is more oxygen-rich.
temperature
A wide temperature range between 15 and 34 ° C is tolerated (nauplii (larvae) up to a maximum of 32 ° C). Temperature fluctuations, such as those that occur alternately between day and night, are unproblematic. Research shows that, on the contrary, they stimulate metabolic activity and the rate of growth.
physiology
nutrition
Triops longicaudatus prefers to stay at the bottom of the water and moves there with the belly side down. There he digs and digs for food with his legs and the reinforced front edge of his back shield. Cancer is an almost insatiable omnivore that can eat up to 40% of its own weight in food every day. In addition to any animal prey that it can overwhelm, such as mosquito larvae and worms to tadpoles, it also consumes vegetable food and carrion and does not stop at freshly skinned conspecifics. But cannibalism only occurs when the density of individuals is too high , a behavior that serves to regulate the natural population. The crustacean can also filter food particles ( planktonic microorganisms and organic detritus ) floating in the water with the help of its bristle leaf legs . By rhythmically beating the leaf bones, the food is then transported from the back to the front of the mouth parts by the negative pressure created in the abdominal groove.
development
Reproduction
The reproductive strategy of Triops longicaudatus is extremely variable, but is subject to local differentiation. For example, unisexual relationships with parthenogenesis (virgin generation) occur quite frequently, i.e. the population consists exclusively of females who continuously produce unfertilized, so-called permanent eggs or cysts without the intervention of males . In contrast to the egg, the embryonic development of the cyst is already completed before it is deposited. In other populations, the animals are hermaphrodites (hermaphrodites) that reproduce through self-fertilization with their hermaphroditic gland. But there are also bisexual populations in which sexual reproduction takes place. There is a continuous spectrum in the gender ratio: from populations with an excess of males to those in which only one percent of all individuals are males.
Cyst
The cysts are extraordinarily resistant and can wait for many years, sometimes even decades (there are indications that it could be centuries) for favorable hatching conditions in the dried-up mud. In the permanent eggs, the embryos are in the gastrula stage in a stasis, a "seemingly dead" state without any metabolic activity, which is known as (egg) diapause . When the habitat then fills with water again, the cycle begins again. However, all nauplii never hatch, and many remain in diapause. This represents an adjustment to the unsafe living conditions, as otherwise too rapid drying out would endanger the existence of the entire population. In this way, some permanent eggs form a “reserve” and only hatch in one of the subsequent floods.
Since the eggs are small and robust, the wind comes into consideration as a possible medium for distributing the cysts and thus for colonizing completely isolated bodies of water. Birds and other animals can also contribute to the spread by transporting the cysts on or even in the body to the nearest body of water, since the digestive tract is passed through intact. As mentioned, Triops longicaudatus can reproduce parthenogenetically, so under favorable circumstances a single egg can be sufficient to completely colonize a new habitat. The nature of the cysts can be seen as the main reason for the remarkable evolutionary success of the genus Triops (and other Branchiopods). This development not only allows them to survive the long dry phase of their waters, but also such catastrophic events in the history of the earth that led to the extinction of dinosaurs, for example .
Nauplius
Already one to two days, depending on the temperature, after they have been covered by water, the approximately 0.2 mm large nauplii hatch from the permanent eggs resting in the mud. After this time, only a few larvae hatch, because they would only be prey for their larger conspecifics that hatched earlier. Hatching is linked to certain triggering conditions:
- The water has a pH value of around 7.0 (neutral) and is poor in dissolved mineral salts
- The eggs lie in a bottom that is completely dry.
- The temperatures are at least 14 ° C
- The eggs are exposed to light
A neutral pH value and a low content of dissolved minerals are characteristic of rainwater. If a previously waterless depression fills with rainwater, the conditions necessary for hatching are given there. This event causes the cysts to hatch and is most effective when the soil has previously dried out completely, otherwise significantly fewer nauplii appear. A different chemistry is caused by the substances dissolved in the water, which have been able to gradually concentrate for a long time through dissolution and evaporation, as is the case with older, drying waters. The high osmotic pressure inside the cyst is therefore the decisive signal for the nauplii to hatch, because it is an indicator of a newly formed body of water. Temperatures below 14 ° C mean unfavorable conditions, so the larvae do not hatch. Frost, on the other hand, does not harm the cysts, but on the contrary leads to a significant increase in the hatching rate. Even under otherwise favorable conditions, the cysts remain in the diapause when they receive no light. This is to prevent that eggs are activated that are trapped deep in the substrate, the nauplii would die. This is prevented by the pores on the surface of the eggs. After the eggs are laid, the pores are filled with fluid so that the cysts do not have any buoyancy. After the pores have completely dried out, the pores contain air, which is why the 0.25 mm eggs float through the smallest openings in the ground into the open water and thus receive the necessary light stimulus.
Triops longicaudatus as Metanauplius
Three hours after hatching
Triops larva seven hours after hatching
After about 15 hours, the nauplius grows into its characteristic shape
After 24 hours, all details are developed as in the adult animal
growth
After hatching, the nauplii are still whitish and translucent; as they grow, the crustaceans turn dark. At the same time, the nauplie is changing from the free-swimming to the ground-oriented ( benthic ) way of life of the adult cancer. In the early larval stages, the body length doubles every day, and the final size is reached correspondingly quickly. Due to the rapid body growth molts are needed at short intervals because the cuticular exoskeleton ( exoskeleton ) is inflexible and unable to grow.
Puberty
Triops longicaudatus is sexually mature after about seven to fourteen days and begins to lay eggs. The permanent eggs are carried on the 11th pair of legs in watch-glass-shaped incubation bags and buried in the ground in batches. At this point in time, the embryonic development is already largely complete, so the nauplii can hatch later with almost no loss of time. During the sexually mature phase, depending on body size and nutritional status, several hundred tiny light to dark red permanent eggs can be laid. It happens that occasionally nauplii hatch spontaneously from the eggs without a preceding drying phase. The life cycle is generally completed after about 6 to 12 weeks, depending on environmental factors such as temperature and food availability. This short life corresponds to the limited lifespan of the habitat.
Economical meaning
In the water rice- growing areas of the USA and Japan, Triops longicaudatus ("riceland tadpole shrimp") can become a pest when reproduced heavily , as it causes damage to the rice plant. In addition, his persistent digging in the mud leads to both the young rice plants being uprooted and the water becoming very cloudy, so that the lack of light affects photosynthesis and thus the growth of the plant. Short- term irrigation of the rice fields is recommended as a measure for biological pest control . After the nauplii have hatched, the field is drained again and the crustaceans dry up. The effect increases accordingly with multiple repetitions.
But its properties as a beneficial insect are also used, for example in Japanese rice cultivation for biological weed destruction, when cultivation has to stop in the fields. Its suitability for combating mosquito larvae has also been proven. In addition, according to studies, the cancer appears to be very suitable for breeding in aquaculture due to its extraordinarily high growth and multiplication rate .
Danger from humans
Triops longicaudatus is, in contrast to some other notostracene in North America as safe; As mentioned above, the species is even assessed as an agricultural pest in rice fields, which is currently also apparently expanding its range to the east. In contrast, the species is considered endangered in Korea.
Trivia
In the comic - magazine Yps . No. 1265 , were held as the type in previous editions "LBs" Artemia salina , "XXL Urzeitkrebse" the kind Triops longicaudatus as a gimmick included.
Individual evidence
- ^ John Lawrence Le Conte (1848): Description of a new species of Apus. Annals of The Lyceum of Natural History of New York 4 (1): 155-156
- ↑ US Fish and Wildlife Service: Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Conservancy Fairy Shrimp, Longhorn Fairy Shrimp, and the Vernal Pool Tadpole Shrimp; and Threatened Status for the Vernal Pool Fairy Shrimp. Federal Register I, Vol. 59, No. 180: 48136,1994
- ↑ Kelly Tindall, Kent Fothergill, W. Minson, Brian Ottis (2009): A New Pest of Rice in Missouri: Range Expansion of Triops longicaudatus (Crustacea: Notostraca: Triopsidae) into the Northern Mississippi River Alluvial Plains. Florida Entomologist 92 (3): 503-505. doi : 10.1653 / 024.092.0314
- ↑ Su Youn Baek, Sang Ki Kim, Shi Hyun Ryu, Ho Young Suk, Eun Hwa Choi, Kuem Hee Jang, Myounghai Kwak, Jumin Jun, Soon-ok Kim, Ui Wook Hwang (2013): Population genetic structure and phylogenetic origin of Triops longicaudatus (Branchiopoda: Notostraca) on the Korean Peninsula. Journal of Crustacean Biology Volume 33, Issue 3: 382-391. doi : 10.1163 / 1937240X-00002142
- ↑ YPS with Gimmick No. 1265: The XXL Tadpole Shrimp. Star Command Communiqué, December 22, 2015, accessed October 16, 2018 .
