New lit.: Phylogenetics of Clitellata

[Geoff Read]

Folks, FYI

Martin, P. 2001. On the origin of the Hirudinea and the demise of the 
Oligochaeta. - Proceedings of the Royal Society London, B 268(1471):1089-
1098.  [Issue of 22 May 2001.]

Abstract: "The phylogenetic relationships of the Clitellata  were 
investigated with a data set of published and new  complete 18S 
rRNA gene sequences of 51 species  representing 41 families. 
Sequences were aligned on the  basis of a secondary structure model 
and analysed with  maximum parsimony and maximum likelihood. In 
contrast to  the latter method, parsimony did not recover the 
monophyly  of Clitellata. However, a close scrutiny of the data  
suggested a spurious attraction between some polychaetes  and 
clitellates. As a rule, molecular trees are closely aligned  with 
morphology-based phylogenies. Acanthobdellida and  Euhirudinea 
were reconciled in their traditional Hirudinea  clade and were 
included in the Oligochaeta with the  Branchiobdellida via the 
Lumbriculidae as a possible link  between the two assemblages. 
While the 18S gene yielded a  meaningful historical signal for 
determining relationships  within clitellates, the exact position of 
Hirudinea and  Branchiobdellida within oligochaetes remained 
unresolved.  The lack of phylogenetic signal is interpreted as 
evidence for  a rapid radiation of these taxa. The placement of 
Clitellata  within the Polychaeta remained unresolved. The 
biological  reality of polytomies within annelids is suggested and  
supports the hypothesis of an extremely ancient radiation of  
polychaetes and emergence of clitellates."

--
  Geoff Read <g.read at niwa.cri.nz>
  http://www.annelida.net/


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