Well, one of the things that I was really interested in (together with one of my graduate students named Rebecca Johnson) was looking at a group of chromodorid nudibranchs that had undergone a lot of diversification. We were interested in looking at their phylogeny to determine their relationships but also to see how that related to different aspects of their biology. We found out yes, that it was a monophyletic group of organisms, that the common ancestor would be here and that these are all of the descendants of that common ancestor.
The other thing that we found out was that there were two major clades or two sister groups in this diversification of this monophyletic group. One of the other interesting things that we found was that in terms of their distribution, that all of the members of this group were found in the Atlantic or the Eastern Pacific. All of the members of this group were found in the Indo-Pacific tropic, basically from the Indian Ocean coast of Africa over to about the Hawaiian Islands. So there was not only a great split in these but their distribution, their vicariance or separation probably was something that had happened long ago.
With nudibranchs that don't have a fossil record, you can only get to approximations of how long ago diversification and splitting of different lineages has occurred. Since some of these are found in the eastern Pacific, we know that it was prior to the closing of the Isthmus of Panama and that's dated at about 3.5 million years. So we know that this lineage has been separated at least prior to that.
|
Narrative Index
BioForum Index
