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
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:ornstn@home.com