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Re: bauplan convergence



At 06:53 PM 14/06/2000 -0400, Dinogeorge@aol.com wrote:
I find this argument very difficult to swallow, but then I don't know much
about insects. Are there any extant aquatic insects that have such propulsive
organs?

Stoneflies are a pretty close example. Ken McNamara and John Long, of the Western Australian Museum in Perth, devote a whole chapter to this subject in their book "The Evolution Revolution" (John Wiley, 1998). To quote some excerpts (p. 95 et seq):


"...Recently Michalis Averof and Stephen Cohen from the European Molecular Biology Laboratory in Heidelberg, Germany, have shown how the presence of two genes that have a wing-specific function in insects (genes called pdm (nubbin) and apterous) also occur in crustaceans. This indicates that the embryonic origin of both insect wings and legs is comparable to the ventral and dorsal branches of crustacean limbs. Averif and Cohen therefore support the idea that insect wings evolved from a gill-like appendage, and suggest that the wings of insects are therefore homologous to the epipodites of crustacean limbs. Epipodites are outgrowths from the main limb in crustaceans which have respiratory and osmoregulatory functions.

"...Some light has recently been shed on this question by James Marden and Melissa Kramer at Pennsylvania State University, on the basis of their studies of stoneflies from the Adirondacks. Stoneflies' wings are too weak to allow them to fly, but they use them like sails on a windsurfer. Being such an ancient group, with fossil remains having been found in Carboniferous rocks, they are useful for formulating models of how insect flight evolved. Marden and Kramer found that by experimentally manipulating the size of the stoneflies' wings, the larger the wings, the faster they could skim across the water. Perhaps this is how wings may have first been used for motion, as intermediate structures derived from structures that were originally used for aquatic respiration. Their first use as tools of locomotion could possibly have been as oars to row across the surface of the water....."

Mcnamara and Long go into considerably more detail, and cite the references in which these and other supporting studies of this very active area of modern insect paleontological and developmental research are published. They also remind us that the earliest fossil winged insects had wings on every thoracic and abdominal segment - just what you would expect, I submit, if they evolved from gills of aquatic arthropods into rowing structures (think of the banks of oars on a galley).


--
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
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