Spider webs untangle evolution
Roxanne Khamsi
Similarity of construction shows 'convergent evolution' applies to
behaviour.

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.

A study of the similarities between the webs of different spider species in
Hawaii provides fresh evidence that behavioural tendencies can actually
evolve rather predictably, even in widely separated places.

Todd Blackledge of the University of California, Riverside, and Rosemary
Gillespie, of the University of California, Berkeley, studied species of
Tetragnatha spiders on different Hawaiian islands. The spiders' webs vary
significantly, with tissue-like 'sheet webs', disorganized cobwebs and
spiral-shaped 'orb webs' as three of the most common types.

Each species had its own characteristic type of web. But the scientists
found that in several cases, separate species of Tetragnatha spiders on
different islands constructed extremely similar orb webs, right down to the
number of spokes, and the lengths and densities of the sticky spiral that
captures bugs.

Was this an example of similar environments producing the same complex
behaviour, or did the spiders with corresponding webs share a common
ancestor?

Full Text at Nature:
http://www.nature.com/news/2004/041101/full/041101-4.html

Posted by
Robert Karl Stonjek
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