Re: Glider questions

["Ralph W. Miller III" <gbabcock@best.com>]

dbensen wrote:

> Really?  I'd never heard of that nymph theory.  Can anyone out there shed some
> light on this?

Jim Marden and Melissa Kramer describe surface-skimming in newly hatched
stoneflies as a locomotory transition between swimming and flying, accomplished 
by
resting the feet on the meniscus of the water and vigorous wing flapping.  
Marden
and Kramer deduced that the ambient streamside temperature was too cold (0 to 12
degrees C) for flapping rapid enough to sustain flight in the thousands of
individuals observed in the field, but the stone flies were none-the-less 
capable
of a rapid enough rate of flapping to enable surface-skimming along the water's
surface to reach the stream's edge where they could crawl out to feed.

At a warmer temperature (22 degrees C), 48 percent of the 31 stone flies tested 
in
the lab were capable of flying to some degree.  The "incompetent" stone flies
(those which could not fly at all) were determined to have had smaller flight
muscles relative to total body weight.  All stone flies observed were capable of
surface-skimming, even in cold weather, and even with 70-80 percent of their 
wing
surfaces trimmed off.

Marden and Kramer suggested that earlier aquatic insects may have paddled by
moving their gill plates, and the bigger the gill plates, the better.  Those 
with
larger gill plates would have had a competitive advantage in feeding and mating,
leading to enlarged gill plates in future generations, evolving into protowings
which permitted surface-skimming.  Subsequent wing enlargement would enable the
animals to fly, giving them access to greater resources.  (I would posit that 
the
selective pressure for stoneflies to fly must not have been overwhelming, or 
they
should be better at it)!  This strategy seems to have been taken somewhat 
further
in their near relatives, the mayflies, which are more competent fliers.  It is
suggested that this scenario parallels the developmental progression seen in 
many
extant insects which begin as wingless, aquatic nymphs, and metamorphose into
winged adults.  The ancestors of modern stoneflies date back to the late
Carboniferous, 330 million years ago, and were characterized by smaller wings 
than
extant varieties.

I read of this research in _Taking Wing_, by Pat Shipman, but here is the 
original
reference:

Marden, J. and Kramer, M. G., "Surface-skimming stoneflies: A possible
intermediate stage in insect flight evolution," _Science_, 1994, p. 427.

-- Ralph W. Miller III       gbabcock@best.com