Portia (genus)

''Portia'' is a genus of jumping spider that feeds on other spiders (i.e., they are araneophagic or arachnophagic). They are remarkable for their intelligent hunting behaviour, which suggests that they are capable of learning and problem solving, traits normally attributed to much larger animals.

Taxonomy and evolution

The genus was established in 1878 by German arachnologist Friedrich Karsch. The fringed jumping spider (''Portia fimbriata'') is the type species.

Molecular phylogeny, a technique that compares the DNA of organisms to construct the tree of life, indicates that ''Portia'' is a member of a basal clade (i.e. quite similar to the ancestors of all jumping spiders), and that the ''Spartaeus'', '' Phaeacius'', and ''Holcolaetis'' genera are its closest relatives.

Wanless divided the genus ''Portia'' into two species groups: the ''schultzi'' group, in which males' palps have a fixed tibial apophysis; and the ''kenti'' group, in which the apophysis of each palp in the males has a joint separated by a membrane. The ''schultzi'' group includes ''P. schultzi'', ''P. africana'', ''P. fimbriata'', and '' P. labiata''.

At least some species of Portia are in the state of reproductive isolation: in a laboratory, male ''P. africana'' copulated with female ''P. labiata'' but no eggs were laid; during all cases the female ''P. labiata'' twisted and lunged in an attempt to bite.

Some specimens found trapped in Oligocene amber were identified as related to ''Portia''.

Distribution and ecology

The 17 described species are found in Africa, Australia, China, Madagascar, Malaysia, Myanmar, Nepal, India, the Philippines, Sri Lanka, Taiwan, and Vietnam.

''Portia'' are vulnerable to larger predators such as birds and frogs, which a ''Portia'' often cannot identify because of the predator's size. Some insects prey on Portia, for example, mantises, the assassin bugs ''Nagusta'' sp. indet. and ''Scipinnia repax''.

Appearance

Portia are relatively small spiders. For example, adult females of ''Portia africana'' are in body length and adult males are long.

Intelligence

''Portia'' often hunt in ways that seem intelligent. All members of ''Portia'' have instinctive hunting tactics for their most common prey, but can improvise by trial and error against unfamiliar prey or in unfamiliar situations, and then remember the new approach.

They are capable of trying out a behavior to obtain feedback regarding success or failure, and they can plan ahead (as it seems from their detouring behavior).

''Portia'' species can make detours to find the best attack angle against dangerous prey, even when the best detour takes a ''Portia'' out of visual contact with the prey, and sometimes the planned route leads to abseiling down a silk thread and biting the prey from behind. Such detours may take up to an hour, and a ''Portia'' usually picks the best route even if it needs to walk past an incorrect route. If a ''Portia'' makes a mistake while hunting another spider, it may itself be killed.

Nonetheless, they seem to be relatively slow thinkers, as is to be expected since they solve tactical problems by using brains vastly smaller than those of mammalian predators. ''Portia'' has a brain significantly smaller than the size of the head of a pin, and it has only about 600,000 neurons.

''Portia'' can distinguish their own draglines from conspecifics, recognizing self from others, and also discriminate between known and unknown spiders.

Hunting techniques

Their favorite prey appears to be web-building spiders between 10% and 200% of their own size. ''Portia'' looks like leaf detritus caught in a web, and this is often enough to fool web-building spiders, which have poor eyesight.

When stalking web-building spiders, ''Portia'' try to make different patterns of vibrations in the web that aggressively mimic the struggle of a trapped insect or the courtship signals of a male spider, repeating any pattern that induces the intended prey to move towards the ''Portia''. ''Portia fimbriata'' has been observed to perform vibratory behavior for three days until the victim decided to investigate. They time invasions of webs to coincide with light breezes that blur the vibrations that their approach causes in the target's web; and they back off if the intended victim responds belligerently. Other jumping spiders take detours, but ''Portia'' is unusual in its readiness to use long detours that break visual contact.

Laboratory studies show that ''Portia'' learns very quickly how to overcome web-building spiders that neither it nor its ancestors would have met in the wild. ''Portia'''s accurate visual recognition of potential prey is an important part of its hunting tactics. For example, in one part of the Philippines, local ''Portia'' spiders attack from the rear against the very dangerous spitting spiders, which themselves hunt jumping spiders. This appears to be an instinctive behavior, as laboratory-reared ''Portia'' of this species do this the first time they encounter a spitting spider. On the other hand, they will use a head-on approach against spitting spiders that are carrying eggs. However, experiments that pitted ''Portia'' against "convincing" artificial spiders with arbitrary but consistent behavior patterns showed that ''Portia'''s instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly.

Against other jumping spiders, which also have excellent vision, ''Portia'' may mimic fragments of leaf litter detritus. When close to biting range, ''Portia'' use different combat tactics against different prey spiders. On the other hand, when attacking unarmed prey, such as flies, they simply stalk and rush, and they also capture prey by means of sticky webs.

''Portia'' can also rely on movement cues to locate prey. In this specific strategy, when potential prey knows it's been seen and stands still to avoid detection, undirected leaps occur in the vicinity of the prey. As a result, the prey will then react to this visual cue, believing itself to have been seen, providing motion that allows ''Portia'' to see and attack it.

''Portia'' may also scavenge corpses of dead arthropods they found, and consume nectar.

Social behavior

Members of the species ''Portia africana'' were observed living together and sharing prey.

If a mature ''Portia'' male meets a sub-mature female, he will try to cohabitate with her.

''P. labiata'' females can discriminate between the draglines of familiar and unfamiliar individuals of the same species. and between their own draglines and those of conspecifics. The ability to recognize individuals is a necessary prerequisite for social behavior.

Vision

''Portia'' species have complex eyes that support exceptional spatial acuity. They have 8 eyes. Three pairs of eyes positioned along the sides of the cephalothorax (called the secondary eyes) have a combined field-of-view of almost 360° and serve primarily as movement detectors. A pair of forward-facing anterior median eyes (called the principal eyes) are adapted for colour vision and high spatial acuity.

The main eyes focus accurately on an object at distances from approximately to infinity, and in practice can see up to about . Like all jumping spiders, ''Portia''s can take in only a small visual field at one time, as the most acute part of a main eye can see all of a circle up to wide at away, or up to wide at away. Jumping spiders' main eyes can see from red to ultraviolet.

The inter-receptor angles of ''Portias eyes may be as small as 2.4 minutes of arc, which is only six times worse than in humans, and is six times better than in the most acute insect eye. It is also clearer in daylight than a cat's vision.

''P. africana'' relies on visual features of general morphology and colour (or relative brightness) when identifying prey types. ''P. schultzi''′s hunting is stimulated only by vision, and prey close by but hidden causes no response. ''P. fimbriata'' use visual cues to distinguish members of the same species from other salticids.

Cross and Jackson (2014) suggest that ''P. africana'' is capable of mentally rotating visual objects held in its working memory.

However, a ''Portia'' takes a relatively long time to see objects, possibly because getting a good image out of such small eyes is a complex process and requires a lot of scanning. This makes a ''Portia'' vulnerable to much larger predators such as birds, frogs and mantises, which a ''Portia'' often cannot identify because of the predator's size.

Movement

When not hunting for prey or a mate, ''Portia'' species adopt a special posture, called the "cryptic rest posture", pulling their legs in close to the body and their palps back beside the chelicerae ("jaws"), which obscures the outlines of these appendages. When walking, most ''Portia'' species have a slow, "choppy" gait that preserves their concealment: pausing often and at irregular intervals; waving their legs continuously and their palps jerkily up and down; moving each appendage out of time with the others; and continuously varying the speed and timing.

When disturbed, some ''Portia'' species are known to leap upwards about often from the cryptic rest pose, and often over a wide trajectory. Usually the spider then either freezes or runs about and then freezes.

Reproduction

''Portia'' exhibits a mating behavior and strategy different from that of other jumping spiders. In most jumping spiders, males mount females to mate. The ''Portia'' male shows off his legs and extends them stiffly and shakes them to attract the female. The female then drums on the web. After the male mounts her, the female drops a dragline and they mate in mid-air. Mating with Portia spiders can occur off or on the web.
The spider also practices cannibalism before and after copulation. The female usually twists and lunges at the mounted male. (''P. fimbriata'', however, is an exception; it does not usually exhibit such behavior.) If the male is killed before completing copulation, the male sperm is removed and the male is then eaten. If the male finishes mating before being killed, the sperm is kept for fertilization and the male is eaten. A majority of males are killed during sexual encounters.

Health

''Portia'' species have a life span of about 1.5 years.

''P. fimbriata'' can regenerate a lost limb about 7 days after moulting.

''Portia''′s palps and legs break off very easily, which may be a defense mechanism, and Portias are often seen with missing legs or palps.

Species

it contains 21 species, found in Africa, Asia, and Australia:
*''Portia africana'' (Simon, 1886) – West, Central Africa, Ethiopia
*'' Portia albimana'' (Simon, 1900) – India to Vietnam
*'' Portia assamensis'' Wanless, 1978 – India to Malaysia
*'' Portia bawang'' (Xu, Peng & Li, 2021) – China (Hainan)
*''Portia crassipalpis'' (Peckham & Peckham, 1907) – Singapore, Indonesia (Borneo)
*''Portia erlangping'' (Xu, Peng & Li, 2021) – China
*'' Portia fajing'' (Xu, Peng & Li, 2021) – China
*''Portia fimbriata'' (Doleschall, 1859) ( type) – Nepal, India, Sri Lanka, Taiwan to Australia
*'' Portia heteroidea'' Xie & Yin, 1991 – China
*'' Portia hoggi'' Zabka, 1985 – Vietnam
*'' Portia jianfeng'' Song & Zhu, 1998 – China
*''Portia labiata'' ( Thorell, 1887) – Sri Lanka to China, Vietnam, Philippines, India
*'' Portia orientalis'' Murphy & Murphy, 1983 – China (Hong Kong)
*'' Portia quei'' Zabka, 1985 – China, Vietnam
*''Portia schultzi'' Karsch, 1878 – Central, East, Southern Africa, Mayotte, Madagascar
*'' Portia songi'' Tang & Yang, 1997 – China
*'' Portia strandi'' Caporiacco, 1941 – Ethiopia
*'' Portia taiwanica'' Zhang & Li, 2005 – Taiwan
*'' Portia wui'' Peng & Li, 2002 – China
*'' Portia xishan'' (Xu, Peng & Li, 2021) – China
*'' Portia zhaoi'' Peng, Li & Chen, 2003 – China

References

Further reading

* D.Harland and R.Jackson. Portia Perceptions: the Umwelt of an Araneophagic Jumping Spider / Complex Worlds from Simpler Nervous Systems. MIT Press, 2004
*
* Harland, D.P & Jackson R.R. (2000): 'Eight-legged cats' and how they see - a review of recent research on jumping spiders (Araneae: Salticidae). ''Cimbebasia'' 16: 231-24
PDF
- vision and behavior in ''Portia'' spiders.
*

External links

Frontal view of ''P. fimbriata''

Information about ''P. fimbriata''
(with distribution in Australia)

* ttps://www.youtube.com/watch?v=usCNem9ixbU Video of ''Portia'' hunting web spiders

{{DEFAULTSORT:Portia (Genus)
Salticidae
Salticidae genera
Spiders of Africa
Spiders of Asia