[olug] OT:, really, really OT: arthropod evolution/phylogeny

[T M]

so far off topic that it is not even on the planet.

As an avid scuba diver, I'm always interested to read marine biology
and am on several marine biology mailing lists.  The following
fascinating story from researchers in academia came across recently:

best,
mike

============
I forgot to send this note back in January.  Our list's own Henrik Glenner
et al. had a short review in the December 22 issue of Science. It's on the
origin of insects.  They state that crustaceans invaded land as insects.
While this is something we all suspected to be true, it looks like they
have the molecular evidence in hand.

Glenner et al. (2005) The Origin of Insects. Science 314: 1883-1884.

I've placed a copy on my ftp site ftp.vims.edu/incoming/shields/crust-l

The upshot is we can now tease our insect-loving colleagues that they're in
fact studying crustaceans....
:-)

============
On a similar note, we can now claim that the insects are the copepods
of the sea..
See Horst Kurt Schminke (In press): Entomology for the copepodologist.
Journal of Plankton Research 2007, abstract to be found at
http://plankt.oxfordjournals.org/cgi/content/abstract/fbl073v1

"Copepods are often called "insects of the seas". Is this justified?
Today insects are regarded as the most successful group of animals.
Measures of absolute success are phylogenetic age (survival through
time), dominance (relative abundance, proportion of total biomass,
role in energy flow, impact on ecosystems and coexisting organisms),
speciosity, geographic range, and breadth of adaptive radiation.
Measured by these criteria copepods are no less successful than
insects.

What about relative success? There must be intrinsic features in the
structure and mode of life of insects which make them more successful
relative to other animal groups. According to the literature these
features are small size, metamorphosis, wings, and mouthparts. If the
capacity to fly is equated with the capacity to swim copepods share
all these intrinsic features being equal with insects also in relative
success. Entomologists believe insects to be unmatched by other groups
in most features of evolutionary success. Yet, they outdo copepods
only in one respect: number of species. Reasons for this are greater
spatial heterogeneity and architectural complexity (of vegetation) on
land than in the sea as well as the fact that insects were among the
first groups on land relatively unaffected by other groups, whereas
copepods had to evolve in an already crowded world."

Cheers,
Peter

============
Dear All

I could not resist elaborating a little on the SYSOP'S mail on the
exciting paper by Glenner et al. Their Science "Comment Paper" reviews
in a very interesting way the new molecular evidence, indicating, not
only that Insects are Crustacea, but that their closest relatives are,
indeed, the Branchiopoda.

Thus, the real centre point of their paper is that this puts insect
(hexapod) origins in an entirely different perspective. It "relieves"
us of seeking marine relatives of the hexapods, since the clade
originated in fresh water. Also, it moves the time perspective so that
the absence of early insect fossils is no longer so problematic.

Obviously, this is pretty controversial. The Branchiopoda ground
pattern (whether reconstructed from Dieter's Rehbachiella in the
Orsten or from the Anostraca) is apparently not close to anything
hexapod like. Also, the new theory does not explain the position of
the allegedly stemline hexapod fossil Devonohaxepodus described a few
years ago by the Waloszek group in Ulm. It also does not explain what
to do with the myriapodous arthropods which none of the molecular put
anywhere near the Crustacea/Hexapoda. Were we all for decenniums
mislead by morphological convergences between myriapods and insects?
If so, the Hexapod folks are about to lose a dear outgroup on which
most of their interpretations have been made. With no outgroup among
the "myriapods", the closes taxon for polarizing characters becomes,
perchance, anostracans, and I bet that will put their character
evolution hypotheses up the creek without a paddle. There is also
evidence from eyes and neuroanatomy that point to a close relation
between the Hexapoda and Remipede/Malacostracan clade. But to which
extent, if any, does these neuroanatomy and eye characters take the
Branchiopoda into account?

At the end of the day, the Glenner et al. paper should therefore be
warmly welcomed as an on time and sobering eye opener that we are
still in for surprises in Arthropod evolution/phylogeny. We most
certainly are not of the woods yet but it is good that branchiopods
have hit the Science pages. After all, the most beautiful and most
friendly looking animal of all is a swimming anostracan......... J

Respectfully
Jens