Tuesday, August 21, 2007

Yet Another Mesoplodont Whale?

Dear Constant Readers,

Ziphiids are among my favorite group of animals, so you can expect me to elaborate on them quite a bit in the future. Beaked whales are the second largest family of cetaceans but also happen to be the most poorly known. Some species are so rarely encountered that they have yet to be ID'd alive (Dalebout et al 2002). Males in the genus Mesoplodon (the largest genus) posses large, distinctive teeth - but as Christ Taylor noted in a comment, identification of females is exceedingly difficult. Future posts will touch on how this even occurs post-mortem in females from time to time.

Lots of interesting things have been happening with this group as of late. Mysterious ziphiids only known from sightings have been classified as have some overlooked old remains. I was wondering if there was some mystery that I haven't heard about that has yet to be solved. Lo and behold...

An unpublished paper by ubiquitous Dalebout (et al) used an approach to uncover hidden biodiversity called "DNA taxonomy". This has been used by other teams to increase the species of Right whales (Eubalaena) to three in recent years, for example. The variability of mtDNA within a species has been found to be very low (less than 1%) with relatively high divergence outside species (over 8%), indicating that the markers are adequate for species identification. The study used large samples sizes (up to six) vs. a previous study done by them (two) to demonstrate that diversity wasn't drastically overestimated - it wasn't. So with an increased database from a "historic" approach (not using morphological characters) an updated phylogenetic tree was created for the group. And lo and behold, some interesting things turned up:

In a subject apparently to be covered in a future paper, it turns out that Mesoplodon mirus (True's beaked whale) may be split into sub-species or even species occupying the Northern and Southern hemispheres. In this paper at least, it is used as a further example that this new phylogenetic tree makes logical groupings.

The focus of this paper is on two skulls recently discovered near Palmyra (Syria) identified as M. ginkgodens (Ginkgo-toothed whale) and a tissue sample from Kiribati (Central Pacific). The Ginkgo-toothed whale itself was first described in 1958 and as of 2002 was known from less than 30 specimens. Despite the skulls being identified by morphology as M. ginkgodens, they formed a distinctive clade with the tissue samples. The Kiribati-Palmyra samples differ by a single diagnostic site and from M. ginkgodens by 26, and posses characters distinct from all other mesoplodonts. Unlike M. mirus, these genetically distinct groups overlap in range. The authors suggest that this should be a distinct species or sub-species, but more work will have to be done to classify it properly. The samples from Kiribati come from either one or two individuals and it is not known if skeletal remains are present.

Since female and juvenile remains have been misclassified in the past, it wouldn't be too much of a surprise for there to be a new species out there. I still haven't heard if scientists are seeing more unclassifiable mesoplodonts at sea though....



Dalebout, Merel L. et al. 2002. A New Species of Beaked Whale Mesoplodon perrini sp.n. (Cetacean: Ziphiidae) Discovered Through Phylogenetic Analyses of Mitochondrial DNA Sequences. Marine Mammal Science. 18, 3: 577-608. Available: Here

Dalebout, Merel L. et al. Published online. A Divergent mtDNA Lineage among Mesoplodon Beaked Whales: Molecular Evidence for a New Species in the Tropical Pacific? Available: Here


Christopher Taylor said...

Evidently, I'm been promoted rather spectacularly. Relax, people, I promise to use my new position fairly, justly and... oh sod that, let's begin some major smiting!

I'm not a fan of DNA taxonomy sans morphology, though I'm glad to see that Dalebout et al. note that:

...caution should be exercised as patterns of genetic divergence, and therefore the location of the barcoding gap, cannot be generalized across species groups...

I did a summer studentship in Scott Baker's lab at the same time as Merel Dalebout was there. Am I a jumped-up little leech for mentioning so?

Anonymous said...

Feel free to yell at me whenever you post a new blog.

Ziphiids are one of my favorite animal groups too, mainly because of the double i's. Any word with double i's is awesome. Currently I can only think of two, not counting plurals.

A ziphiid went skiing. Now that's one awesome sentence.