IN REPLY TO THE FOLLOWING MESSAGE: (see below)
>From: harley at uctvax.uct.ac.za
>Subject: The outgroup problem
>Date: 4 Jun 93 09:03:36 GMT
>Reply-To: harley at chempath.uct.ac.za
>
>I have a topic which might engender some constructive debate, and
>can be put as the proposal *the outgroup is not appropriate as a
>way of rooting molecular phylogenies*. This is, of course, a bit
>extreme, but I am coming to the conclusion from looking at a
>number of sequence data sets that one is caught between the devil
>and the deep blue sea: if the outgroup is too close it may not
>really be a valid outgroup, if too far then the number of sites
>genuinly identifying the plesiomorphic state may be too few, and
>mixed with so many homoplasies (back & parallel mutations, esp if
>there is a high transition bias) as to be worse than useless.
>Put another way, is there a statistical method which will define
>a window ( of distance ? of shared sites ?) within which a
>particular taxon can be used as a valid outgroup. What is good
>for morphologists may not be so good for gene jocks.
REPLY:
We are working on that very problem (how distant is a too distant
outgroup). We are using species groups with well established
phylogenies and sequencing mitochondrial 12S, 16S, CO2, and CytB
genes. These groups include a hierarchical set of taxa for
rodents starting with several Peromyscus species and ending with
Rattus and Mus; Drosophila, starting with D. melanogaster group
and ending with D. virilis (in collaboration with L. Nigro, U.
Padova); we are also studying various other groups of insects
whose phylogenies are less well known. We are finding that the
distance of the appropriate outgroup varies depending on the
genes studied. Ribosomal genes are particularly troublesome. We
will be presenting some of our results at the Evolution meetings
in Snowbird Utah in June and in Montpelier (by L. Nigro and F.
Frati) in August. We are currenlty writing the first of a series
of papers on the subject.
Chris Simon
Jack Sullivan
CHRIS SIMON PHONE: 203-486-4640
ECOL. EVOL. BIOLOGY U-43 FAX: 203-486-6364
UNIVERSITY OF CONNECTICUT BITNET: CSIMON at UCONNVM
STORRS, CT 06269 INTERNET: CSIMON at UCONNVM.UCONN.EDU
