What does paraphyletic REALLY mean? (1 Viewer)

[njlarsen]

The questions is precipitated by something I read in both Clements and IOC: that Paradoxornis was paraphyletic if Reed Parrotbill was included, and it is therefore moved to Calamornis. I understand paraphyletic as meaning that there is some other taxon that separates these two. However, both lists keep the two daughters as nearest neighbors. If there was some other taxon separating them, should that not be reflected in the linear order after this split?
Hope this is understandable?
Niels

 

[THE_FERN]

Not sure about some taxon separating them: more like you've a taxon which includes some but not all of the twigs from its sub-branches. Those twigs ought to be included because they're descended from the same common ancestor... ...but they're not.

Linear sequences can usually only approximately reproduce the patterns of relatedness you get in phylogenetic trees. This is most obviously true where things arise through hybridisation (plants but probably quite a few birds). Here 2 different, perhaps "distant" relatives would have to be next to each other but that would mess up the rest of the tree.

 

[D Halas]

As THE_FERN says, the issue is that linear sequences can't capture the full structure of a phylogenetic tree. In a proper linear sequence of species, all species that are each other's closest relatives will necessarily be adjacent in the sequence, but not all species that are adjacent in the sequence are each other's closest relatives. In the IOC sequence, for example, the Rodrigues Parrot is immediately adjacent to the Rifleman, a New Zealand wren.

In the case of the Reed Parrotbill, it turns out that the other two parrotbills are more closely related to the genera Conostoma, Cholornis, and Psittiparus than they are to the Reed Parrotbill. Since these genera follow Paradoxornis in the sequence, Calamornis remains adjacent to Paradoxornis in a linear ordering.

 

[thyoloalethe]

The old Paradoxornis (that included all Parrotbills except Great) is paraphyletic if Conostoma and Chamaea are excluded. In order to keep these last two, Paradoxornis had to be broken up into a number of genera. Keeping Conostoma forces the placement of Reed Parrotbill in Calamornis. See this tree (note that in this example Conostoma still became enlarged to incorporate two other species).

 

[njlarsen]

Thank you everyone, these answers clarified my confusion.
Niels