Porcellio scaber

Porcellio scaber (otherwise known as the common rough woodlouse or simply rough woodlouse), is a species of woodlouse native to Europe but with a cosmopolitan distribution. They are often found in large numbers in most regions, with many species (shrews, centipedes, toads, spiders and even some birds) preying on them.

Porcellio scaber
P. scaber, head is left
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Superorder: Peracarida
Order: Isopoda
Suborder: Oniscidea
Family: Porcellionidae
Genus: Porcellio
Species:
P. scaber
Binomial name
Porcellio scaber

Distribution

Porcellio scaber is found across Central and Western Europe.[2] In the United Kingdom, it is one of the "big five" species of woodlice. It has also colonised North America, South Africa and other regions including the remote sub-Antarctic Marion island, largely through human activity.[3] It is also the most common species of woodlice found in Australia.[4]

Description

Porcellio scaber has an oval body, can grow up to 20 millimetres (0.79 in) long, and is usually a grey colour, paler underneath, although brown, blue, yellow, or pinkish hues may also be observed (like many other woodlice, a red variety can often be found in coastal areas). The dorsal (upper) surface of its segmented exoskeleton is covered in a series of small tubercles hence its common name.

At the head it has two pairs of antennae, with the inner pair being very small. Two compound eyes are located on the dorsal side of the head, while the mouth parts are on the ventral (lower) side.

There are 7 pairs of legs, corresponding to the 7 segments of the thorax. The short abdomen consists of 6 segments.[5] On the ventral side of the abdomen there are two whitish pseudo-lungs, connected with pores to the outside air. At the rear end there is a small telson flanked by a pair of appendages known as uropods.[5]

Head with antennae and compound eyes

Habitat

Porcellio scaber loses water by diffusion through its permeable exoskeleton which lacks a waxy cuticle. Because of this, to avoid desiccation, it often seeks out environments with humid air and plenty of ground moisture, preferably cold to minimize rate of water loss, and dark to avoid detection by predators. It lives in a wide variety of damp habitats but it is less dependent on high levels of humidity than Oniscus asellus.[6]

Feeding

Porcellio scaber is a detritivore - it mainly feeds on decaying leaf litter but will consume any rotting plant matter. Living plants are of limited nutritional value for these woodlice which prefer to feed on the bacteria and fungi which cause decay.[7] P. scaber has very sensitive olfactory receptors that allow it detect the smell of microbial activity and to locate food.[8]

Life cycle

The females carry about 25 to 90 fertilized eggs until they hatch and are held in a fluid-filled sac at the ventral side of the abdomen for about 40-50 days. The young are fully grown after 3 months; the adult animals have a life expectancy of about two years.[5]

Ventral side

Behaviour

Porcellio scaber respond to certain stimuli with kinesis behaviour. To attempt to find an environment where they lose less moisture and then stay there, P. scaber alter factors such as speed and rate of turning (orthokinesis and klinokinesis). When in a dry or hot environment, these woodlice have been observed increasing speed and turn more often in an attempt to leave the unfavorable environment. In a moist, dark, cool environment, they slow down dramatically and often stop altogether. To avoid desiccation, most woodlice (including P. scaber) exhibit thigmokinesis, slowing down or stopping when in contact with multiple surfaces(such as the corner of a box or a crack between two bricks). This behaviour leads to clumping of woodlice, reducing the exposed surface area through which water can be lost. Another manifestation of this is that a woodlouse in a Petri dish is unwilling to move into the center of the dish, preferring to stay near the edge.

Another reflex exhibited by P. scaber is turn alternation. During klinokinesis, turns alternate between left and right. This helps the woodlouse escape from a harmful environment or predator more efficiently as alternating turns average to form a straight line, unlike random turns which may well become a circle back to the predator. Several mechanisms for this have been proposed, such as short-term memory or following the outside wall, but the theory with most support is the bilateral asymmetrical leg movement (BALM) mechanism, which suggests that on the original turn, the legs on the outside of the turn become relatively more tired, so end up being overpowered by the legs on the inside of the turn, causing it to turn the opposite way from last time.[9]

Unlike the 'roller' species of woodlouse, such as Armadillidium spp., which are able to curl into a ball to defend themselves, P. scaber is a 'clinger' and adopts a posture of tonic immobility when faced with the threat of predation. A study of this thanatosis behaviour found that individuals of this species had unique personalities with shy woodlice staying still for longer and bold woodlice staying immobile for less time.[10]

Algorithm

Inspired by the behaviours of P. scaber, an algorithm for solving constrained optimization problems was proposed, called the Porcellio scaber algorithm (PSA).[11][12]

See also

References
  1. "Porcellio scaber". Integrated Taxonomic Information System.
  2. "Porcellio scaber". 2.6.1. Fauna Europaea. May 24, 2013. Archived from the original on June 29, 2011. Retrieved May 25, 2013.
  3. Slabber, S.; Chown, S. "The first record of a terrestrial crustacean, Porcellio scaber (Isopoda, Porcellionidae), from sub-Antarctic Marion Island". Polar Biology. 25 (11). doi:10.1007/s00300-002-0420-9. ISSN 0722-4060.
  4. Sandra Hangartner; Garry McDonald (February 2015). "Slaters: Armadillidium vulgare & Porcellio scaber" (PDF). South Australian Research and Development Institute (SARDI). Retrieved 2 August 2018.
  5. "Kellerassel" (PDF). Stadt Zürich - Umwelt- und Gesundheitsschutz (in German). November 2011.
  6. "Porcellio scaber - a woodlouse". Natural England. Archived from the original on April 5, 2011. Retrieved January 19, 2009.
  7. Horvathova, Terezia; Babik, Wieslaw; Bauchinger, Ulf (2016-04-05). "Biofilm feeding: Microbial colonization of food promotes the growth of a detritivorous arthropod". ZooKeys (577): 25–41. doi:10.3897/zookeys.577.6149. ISSN 1313-2970. PMC 4829882. PMID 27110187.
  8. Zimmer, Martin; Kautz, G; Topp, W (1996-01-01). "Olfaction in terrestrial isopods (Crustacea: Oniscidea): Responses of Porcellio scaber to the odour of litter". European Journal of Soil Biology. 32: 141–147.
  9. Hughes, R. Cite journal requires |journal= (help); Missing or empty |title= (help)
  10. Tuf, Ivan Hadrián; Drábková, Lucie; Šipoš, Jan (2015-07-30). "Personality affects defensive behaviour of Porcellio scaber (Isopoda, Oniscidea)". ZooKeys (515): 159–171. doi:10.3897/zookeys.515.9429. ISSN 1313-2970. PMC 4525042. PMID 26261447.
  11. Zhang, Yinyan; Li, Shuai (2017-09-28). "PSA: A novel optimization algorithm based on survival rules of porcellio scaber". arXiv:1709.09840 [cs.NE].
  12. Zhang, Yinyan; Li, Shuai; Guo, Hongliang (2017). "Porcellio scaber algorithm (PSA) for solving constrained optimization problems". MATEC Web of Conferences. 139: 00033. arXiv:1710.04036. doi:10.1051/matecconf/201713900033. ISSN 2261-236X.
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