NATURE cover story critical review

[Kip]

***The following is a reply to the recent cover article in Nature (Vol
377 #6547) by J.  Marden & M. Kramer (referred to as M&K below).
Please refer to the notes section below for more on citations and
distribution of this message.***


Plecoptera skimming and the origin of insect flight revisited.

     I would first restate my response (Technical comment, Science in
press, accepted 24 Aug 1995) to M&K's original Science article.  The
observation of skimming behavior and the increased performance in
skimming ability are not sufficient grounds to promote the notion that
skimming in Plecoptera is a precursor to flight in insects.  This
hypothesis is not founded on phylogenetic analyses.  In their article
phylogenetic evidence, when present, is  misrepresented.  In
fact,  M&K would ignore phylogeny in order to accommodate a
evolutionary scheme that is largely a just-so story. Most recently M&K
have continued to peddle this idea in the popular
journal Nature.
  This article attempts to totally side-step phylogeny.  In what can
only be viewed as a paradox M&K start the article by invoking
"several flight-related traits" found in Plecoptera, thought to be
primitive, and then end by calling for a de-coupling of flight and
wing evolution.  They seem to be victims of their own inability to
separate function from form. Phylogenies for insect orders are based
on a suite of characters not on wing-use itself.  If M&K want a
de-coupled analysis look at the literature. Take the best
supported phylogenetic hypothesis and observe the pattern of wing use
on the cladogram.  Does the position of skimming behavior relative to
aerial flight suggest a primal occurrence of skimming? Can the many
well collaborated homologies, both molecular and morphological be
overturned by the several characters of a single specialized linage?
Clearly, the answer to both is no.

     The "apparent homologies" of wings referred to by M&K are
homologies as clearly as the femur of any two insects are homologs. If
they have evidence to the contrary it should be stated.  It would seem
they have none to present.  In lieu of conclusive evidence for their
position that Plecoptera are somehow exemplars of the primitive
pre-flight insect they show a picture of the Dipluran family
Campodeidae to show the "gross morphological similarity" to
Plecoptera.  That is not evidence.  It is a comparison of ancestral
similarities or worse, phenetic similarity.  Ancestral similarity
contains no information for defining distinct (monophyletic) linaeges,
e.g. the problems with "reptile" and bird relationships.  Phenetic
comparisons are confounded by paralleisms and convergences, for
instance, grouping ducks and platypuses based on bills, webbed feet
and egg laying.  M&K  have yet to present any evidence that Plecoptera
are primative or their use of wings for skimming is an ancestral
condition.

     The phraseology in M&K's  article is elusive and non-committal.
It is obviously intended to hedge all bets while attempting to lead
the reader to unsupported conclusions.  Anything beyond the fact that
these Plecoptera are skimming and that skimming improves as the wing
size increases is totally illusory.  M&K have left the realm of logic
when they propose several evolutionary origins of flight.  Under their
assumption at least seven independent origins must be postulated (look
for my cladograms, Science, in press).  It is certainly possible to
outline a very intricate scenario with a high level of plausibility.
Applying their logic it is equally probable that using the hind legs
for jumping locomotion, as in Orthoptera, is primitive and tripod
walking has been derived multiple times.  M&K's hypothesis, when
scrutinized in full light, lacks substantive evidence.


NOTES:

Look to J.  Marden's www home page for his list of complete references
to the articles in question above.  The original Science article
(M&K)appeared in Oct 94, the technical comment (K.Will) was submitted
in Apr 95, and accepted in Aug 95, the Nature article (M&K)was
submitted June 95 accepted Aug 95.

References to any subject noted above can be provided upon request.

This message is posted on sci.bio.ecology, sci.bio.entomology.misc,
sci.bio.evolution, sci.bio.systematics and has been forwarded to
Nature.

I strongly encourage everyone to post comments publicly.


Kipling W. Will
Department of Entomology
Cornell University