Leg tinker

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Leg tinker
Proturo2.png

Leg tinker ( Protura )

Systematics
Over trunk : Molting animals (Ecdysozoa)
Over trunk : Molting animals (Ecdysozoa)
Trunk : Arthropod (arthropoda)
Superclass : Six-footed (Hexapoda)
Class : Sackkiefler (Entognatha)
Order : Leg tinker
Scientific name
Protura
Silvestri , 1907

The leg taster (Protura) are an order of the six-footed . Of the 748 species of the group known in 2007, around 200 are also distributed in Central Europe. The species are morphologically extremely similar and can only be differentiated by a handful of specialists worldwide. The leg tinker was not discovered until 1907, by a hobby zoologist near Genoa.

Leg tinkerers live mainly in the ground, to a depth of about ten centimeters. In general, they love moisture and suck out fungal threads in the soil.

Construction of the leg tinker

Leg tinkerers are 0.5 to 2.5 millimeters long. They are usually white or translucent colorless, rarely yellow or orange, with the rear end often more vividly colored. Only the genus Sinentomon is strongly red-brown in color. The body can each have a pair of simple and unconnected, tubular trachea , the openings (spirals) of which are located on the second and third trunk segments. But these can also be completely absent.

Head and mouthparts

The head of the Protura is small in relation to the body size, it is round to pear-shaped, with a slightly triangular point towards the front. The mouthparts point forward (prognath). Neither eyes nor antennae are developed. On the surface of the head there are only two button-shaped, bulging, dome-shaped organs, which are called pseudoculi, these are probably chemical sensory organs. The mouthparts are enclosed in a tubular protuberance in the head wall and are not freely visible (entognath); this tube is not completely closed, but rather shows a suture (linea ventralis) on the underside. The mouthparts are designed as stiletto-like piercing bristles. They serve the animal primarily to pierce and suck out fungal threads ( hyphae ). The mandibles, one or both branches of the maxilla and both branches (ligula) of the labium are involved as piercing bristles. The palps of the maxillae are quite long and protrude from the sheath of the mouthparts, they consist of three (rarely four) segments. The labial palps are small and inconspicuous and usually only one segment.

Inside the head there is an internal skeleton, which is disputed as to whether it is homologous to the tentorium of the other Hexapoda .

Torso and legs

The trunk of the leg probe consists of three segments, typical of the hexapod, with the first segment being significantly smaller than the two following. Each segment has a belly plate (sternite), a back plate (tergite) and several small, separate sclerites (pleurites) on the sides. In addition, each segment carries a pair of legs. Only the two rear pairs of legs are used as walking legs. The forelegs are lifted and carried forward in life, they serve as sensory organs and have essentially taken over the functions that the antennae have in other arthropods. The legs show the typical structure of the hexapod legs in coxa, trochanter, femur, tibia and tarsus. The tarsi are single-segment. The pretarsus of each leg has a simple claw.

Abdomen

The abdomen of the Protura is elongated, cylindrical, slightly pointed towards the rear end. It consists of twelve clearly recognizable segments and thus has one more segment than any other Hexapoda. The twelfth segment is often referred to as the telson, this name goes back to a hypothesis about its development and homology in other arthropods, but it does not differ in its structure from the others. At the rear end, it has a tongue-shaped appendix sometimes called a furca. Paired cerci are missing. The segments eight to twelve can be drawn in telescopically into the rear end and everted out again. The first three abdominal segments have short extremities (so-called styli ) on the abdomen . The first pair of these consists of two segments, each with an evertable vesicle at the end. Those of the second and third segments can be built similarly or reduced to bud-like rudiments. A pair of large glands open out at the eighth segment, which are interpreted as defensive glands to ward off enemies, they give off a tough, sticky secretion. However, this has so far only been directly demonstrated for one species ( Acerentulus sp.).

The external genitalia of the Protura are built very similarly in both sexes. They consist of two basal arms, each with an attachment (stylus). In the case of the males, the genital orifices lie on the arms (they are therefore paired), in the case of the females the only genital opening is on the basal body between them. In the resting position, they are withdrawn into a genital chamber, which opens on the abdominal side between the abdominal plates (sternites) eleven and twelve, and can be stretched forward. Nothing is known about mating and fertilization in this group. It is not even clear whether there will be direct fertilization or whether the male will deposit a spermatophore which is only then ingested by the female (indirect fertilization). The structure of the sperm (with an immobile flagellum ) tends to suggest indirect fertilization.

Reproduction and development

The females of the Protura lay eggs that are either smooth or have a rough surface, which may be used to hold air in the event of flooding (plastron). A prelarve with nine abdominal segments hatches from the egg and does not consume any food. This sheds its skin at the first larval stage, also with nine abdominal segments. The second larval stage then has ten abdominal segments. This sheds its skin in a stage called "Maturus junior" with twelve abdominal segments. This stage is either followed by the sexually mature animal, or a subimaginal stage is inserted, which differs from the imago only in the sex organs that are not yet functional. The course of development in which postembryonic larval stages gain segments when moulting is called anamerism or anamorphosis. The Protura are the only Hexapoda with anamorphosis.

The development time of the individual stages and their annual cycle are obviously quite variable. A one-year development cycle is usually assumed. Imaginal animals are present year round. In winter they do not retreat to deeper soil layers.

Although it is possible to use special techniques to keep leg tinkers alive in the laboratory for a long time, and there is also isolated evidence of eggs and young animals under such conditions, all attempts at breeding over several generations have so far failed.

ecology

Leg tinkerers are soil organisms. They live in the system of gaps in the soil, including the humus (individual observations have also been made from rotted dead wood or moist, partially decomposed plant residues). They usually never come to the surface of the soil voluntarily. However, they remain limited to the upper soil layers, and no animal has been found deeper than about 50 centimeters below the surface.

From the observations made so far, a diet is assumed to be preferably fungal hyphae. The animals are able to pierce the cell wall with their piercing-bristle-like mouthparts and then suck out the inside. Numerous authors assume that at least most species are closely related to mycorrhizal fungi ; these are types of fungus that live in symbiosis with plant roots. The extent to which a different diet is possible and occurs is controversial. Earlier observations of a predatory diet are now considered implausible. The animals can starve for a long time; in the laboratory they survived for up to seven weeks without eating.

Protura live in soils of all kinds. However, their population density should be higher in acidic soils than in basic ones. Their population density in various soils has been determined in numerous studies (mainly from forest soils) to be between about 2,000 and 18,000 individuals per square meter of soil. This makes them an order of magnitude rarer than the similarly small mites and springtails . Almost nothing is known about their ecological importance in the habitat. As a rule, numerous species are found in their habitats, the highest species density ever found in one place was 23 species in a green space in the city of Vienna.

Leg tinkerers are almost impossible to find in the ground with the naked eye when searching directly. They are usually driven out of the soil for examination by heat extraction ( Berlese extraction). It is possible, but less common, to separate them using flotation.

Phylogeny

The leg tinkers are classically combined within a common group with the springtails (Collembola) and double tails (Diplura) as sack-jaws (Entognatha) and contrasted with the free-jaws (Ectognatha) or insects as a sister group. The reason for this taxon formation is the mouth pocket in which the mouthparts are located and which is present in all three groups. This grouping has been questioned several times for morphological reasons and based on analyzes of the mitochondrial DNA, but is still considered the most likely hypothesis. Within the Entognatha two hypotheses are usually contrasted: Either the Protura and Collembola form a common group, which is then called "Ellipura". Or the Protura and the Diplura form a common group, which in this case is called "Nonoculata" (after the missing eyes).

Molecular studies (based on homologous DNA sequences) have confirmed the Nonoculata hypothesis , with a few exceptions . However, these results are preliminary and not yet sufficiently confirmed. The problem is that so far only a few types of leg tracer have been sequenced. In addition, their sequence is very different from that of the other groups and shows an unusual preponderance in favor of the bases guanine and cytosine in the composition. The mitochondrial DNA is the only one that has been fully analyzed and shows numerous structural deviations and peculiarities. These factors can trigger a so-called "long-branch attraction" (roughly: attraction of long branches). Unusual sequences in the analysis are more or less "pushed away" to the edge and can thus enter into an artificial grouping as an artifact in the analysis. Up to now, one obstacle to processing was that the leg taster individuals had to be mounted on microscope slides for reliable morphological determination (under the transmitted light microscope), which meant that it was no longer possible to obtain material for DNA analysis. Due to the great similarity of the species to each other, one could either determine the species or sequence the animal - but not both. This problem has only recently been resolved.

Systematics

A leg taster of the genus Acerentomon

The leg tinkerers are usually divided into three groups, which in the classical system receive the rank of subordination.

swell

  • Heinz Janetschek: Order Protura (leg taster). In: Handbook of Zoology. A natural history of the tribes of the animal kingdom. 14. Delivery. De Gruyter Verlag, 2nd edition 1970. ISBN 3-11-006373-5 .
  • OW Richards & RG Davies: Protura. In: Imms' General Textbook of Entomology. Springer Verlag, 1977. ISBN 978-0-412-15230-6
  • SL Tuxen: Protura (Insecta). In: CT Duval (editor): Fauna of New Zealand, Number 9. 1985. ISBN 0-477-06765-4

Individual evidence

  1. ^ A b Andrzej Szeptycki (2007): Catalog of the world Protura. Wydawnictwa Instytutu Systematyki i ewolucji Zwierzyt Polskiej Akademii Nauk. Kraków.
  2. ↑ http://oe1.orf.at/programm/395430 From the life of nature. Unknown primal insects. The zoologist Günther Pass talks about the leg tinkerers. Part 1: wingless tiny creatures. Ö1 (ORF) radio broadcast from January 26, 2015, 8:55 am (series has 5 parts)
  3. ↑ a b c d Günther Pass & Nikolaus Urban Szucsich (2011): 100 years of research on the Protura: many secrets still retained. Soil Organisms Volume 83 (3): 309-334.
  4. ↑ B. Bacchetti, R. Dallai, B. Frattello (1973): The spermatozoon of Arthropoda XXII: the 12 + 0, 14 + 0 or aflagellate sperm of Protura. Journal of Cell Science 13: 321-335.
  5. ↑ Ryuichiro Machida, Ichiro Takahashi (2004): Rearing technique for proturans (Hexapoda: Protura). Pedobiologia 48: 227-229. doi: 10.1016 / j.pedobi.2003.01.001
  6. ↑ Dell'Ampio, E., NU Szucsich, A. Carapelli, F. Frati, G. Steiner, A. Steinacher, G. Pass (2009): Testing for misleading effects in the phylogenetic reconstruction of ancient lineages of hexapods: influence of character dependence and character choice in analyzes of 28S rRNA sequences. - Zoologica Scripta 38: 155-170.
  7. ↑ a b Emiliano Dell'Ampio, Nicholas Urban Szucsich, Günther Pass (2011): Protura and molecular phylogenetics: status quo of a young love. Soil Organisms Volume 83 (3): 347-358.
  8. ↑ Wan-Jun Chen, Yun Bu, Antonio Carapelli, Romano Dallai, Sheng Li, Wen-Ying Yin, Yun-Xia Luan (2011): The mitochondrial genome of Sinentomon erythranum (Arthropoda: Hexapoda: Protura): an example of highly divergent evolution. BMC Evolutionary Biology 11: 246 open access
  9. ↑ Alexander Böhm, Daniela Bartel, Nikolaus Urban Szucsich, Günther Pass (2011): Confocal imaging of the exo- and endoskeleton of Protura after nondestructive DNA extraction. Soil Organisms Volume 83 (3): 335-345.

Web links

Commons : Protura  - collection of images, videos and audio files