Origins of Hexapoda

[John Grehan]

Ken,

Just as a matter of general interest could you list the characters you see
as connecting collembolans with ostracods? Also, how do your characters
stand up against the characters proposed for the other alternative
relationships?

John Grehan

At 10:45 PM 5/4/2004 -0500, Ken Kinman wrote:
>Dear All,
>       Among those who believe Collembola are not directly related to
> forktails and insects (and there are many such workers), there seems to
> be three main hypotheses:
>   (1) P.N. Lawrence, who believes they are related to amphipods.  Doubts
> have been expressed about this option.
>   (2) others who believe collembolans are sister group to Branchiopod
> crustaceans (supported by an 18S rRNA analysis in 1997 by Spears and Abele).
>   (3) collembolans related to ostracods (my new hypothesis).
>
>      Unfortunately, some of Spears and Abele's (1997) trees show a
> polyphyletic Ostracoda, so this makes me wonder just how reliable 18S
> rRNA sequences are in solving this particular problem.  The preponderance
> of evidence convinces me that Collembola evolved from a crustacean
> group.  I still see no good reason to abandon my ostracod hypothesis, but
> if I do, Brachiopoda would be a good second choice.  On the other hand,
> Insecta (ectognathous hexapods) probably evolved from some group of
> malacostracan crustaceans.  If they have separate crustacean sister
> groups, then two or more origins of hexapods will obviously make Hexapoda
> polyphyletic.  And for those who might be wondering, if forktails
> (diplurans) are not sister group to the ectognathous Insecta, then they
> may be sister group to another malacostracan taxon, but I am not ready to
> tackle that one until I get the collembolans placed.
>               ------ Cheers,
>                           Ken Kinman

Dr. John Grehan
Director of Science and Collections
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