T
The_Barbarian
Guest
Barbarian observes:
Because web shape is determined by a great number of factors, including temperature, size of the spider, the sort of silk produced, and so on.
No single gene determines all those things. Some are not even determined by genes at all.
Design variability in web geometry of an orb-weaving spider
Auteur(s) / Author(s)
VOLLRATH F. (1 2) ; DOWNES M. (1) ; KRACKOW S. (2 3) ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
(1) Department of Zoology, Universitetsparken B135, 8000 Aarhus, DANEMARK
(2) Department of Zoology, South Parks Road, Oxford OX1 3PS, ROYAUME-UNI
(3) Abt. Sinnesbiol. Inst. f. Biol., Humboldt-Universität, Invalidenstr. 43, 10115 Berlin, ALLEMAGNE
Résumé / Abstract
We studied the effect of several variables (environmental and physiological) on web geometry in the garden cross spider Araneus diadematus. Variables were: web support, wind, temperature, humidity, and silk supply. All had an effect. The spiders generally attempted to fit their webs to the shape of the supporting frame (standard, small, vertical, or horizontal). Windy conditions (0.5 m s-1) during web construction caused spiders to build smaller and rounder webs, laying down fewer capture spirals while increasing the distances between capture-spiral meshes. Decreasing temperature from 24° to 12°C caused the capture spiral to have fewer and wider spaced meshes, which did not change overall capture area but reduced the length of capture-spiral threads laid down. Subsequent increase of temperature to 24°C restored the number of meshes laid down, but the wider mesh was retained, causing the capture area to be increased over initial control values. Decreased humidity (from 70 to 20% rH ) had the effect of reducing web and capture-spiral size, the latter by reducing mesh number while keeping mesh spacing constant. Subsequent increase of humidity to control level (70%) restored web and capture area. However, this was achieved by laying down capture meshes at larger distances, rather than returning to initial mesh numbers. Silk supply also had a strong effect. Webs built in unnaturally rapid succession by the same spider (4 in 24 h when I is the norm) became sequentially smaller, had fewer radii, shorter capture spirals, and were wider meshed.
cat.inist.fr/?aModele=afficheN&cpsidt=2791985
Oh, and there are still pre-web spiders. Wolf spiders, for example.
And evolution of silk-spinning? There’s some evidence…
**Spider webs untangle evolution
Similarity of construction shows ‘convergent evolution’ applies to behaviour.
Roxanne Khamsi
The biologist Stephen Jay Gould famously proposed that if we could “rewind the tape” of evolution and play it again, chance would give rise to a world that was completely different from the one we live in now. But the concept that chance reigns supreme may ring less true when it comes to complex behaviours.**
nature.com/news/2004/041101/full/news041101-4.html
Because web shape is determined by a great number of factors, including temperature, size of the spider, the sort of silk produced, and so on.
No single gene determines all those things. Some are not even determined by genes at all.
Well, let’s take a look…
Design variability in web geometry of an orb-weaving spider
Auteur(s) / Author(s)
VOLLRATH F. (1 2) ; DOWNES M. (1) ; KRACKOW S. (2 3) ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
(1) Department of Zoology, Universitetsparken B135, 8000 Aarhus, DANEMARK
(2) Department of Zoology, South Parks Road, Oxford OX1 3PS, ROYAUME-UNI
(3) Abt. Sinnesbiol. Inst. f. Biol., Humboldt-Universität, Invalidenstr. 43, 10115 Berlin, ALLEMAGNE
Résumé / Abstract
We studied the effect of several variables (environmental and physiological) on web geometry in the garden cross spider Araneus diadematus. Variables were: web support, wind, temperature, humidity, and silk supply. All had an effect. The spiders generally attempted to fit their webs to the shape of the supporting frame (standard, small, vertical, or horizontal). Windy conditions (0.5 m s-1) during web construction caused spiders to build smaller and rounder webs, laying down fewer capture spirals while increasing the distances between capture-spiral meshes. Decreasing temperature from 24° to 12°C caused the capture spiral to have fewer and wider spaced meshes, which did not change overall capture area but reduced the length of capture-spiral threads laid down. Subsequent increase of temperature to 24°C restored the number of meshes laid down, but the wider mesh was retained, causing the capture area to be increased over initial control values. Decreased humidity (from 70 to 20% rH ) had the effect of reducing web and capture-spiral size, the latter by reducing mesh number while keeping mesh spacing constant. Subsequent increase of humidity to control level (70%) restored web and capture area. However, this was achieved by laying down capture meshes at larger distances, rather than returning to initial mesh numbers. Silk supply also had a strong effect. Webs built in unnaturally rapid succession by the same spider (4 in 24 h when I is the norm) became sequentially smaller, had fewer radii, shorter capture spirals, and were wider meshed.
cat.inist.fr/?aModele=afficheN&cpsidt=2791985
Oh, and there are still pre-web spiders. Wolf spiders, for example.
And evolution of silk-spinning? There’s some evidence…
**Spider webs untangle evolution
Similarity of construction shows ‘convergent evolution’ applies to behaviour.
Roxanne Khamsi
The biologist Stephen Jay Gould famously proposed that if we could “rewind the tape” of evolution and play it again, chance would give rise to a world that was completely different from the one we live in now. But the concept that chance reigns supreme may ring less true when it comes to complex behaviours.**
nature.com/news/2004/041101/full/news041101-4.html