Molecular phylogeny of the elephantids

The traditional view of phylogenetic relationships among the elephants (i.e., including mammoths), based on skeletal and dental morphology, is that Mam-muthus is more closely related to Elephas than it is to Loxodonta. In their detailed cladistic analysis of the proboscideans and related mammalian orders, Pascal Tassy and Jeheskel Shoshani note "a sister-group relationship" between Elephas and Mammuthus based on morphology, although they recognize that the biochemical data do not support such a strong relationship. It is easy to see that features such as the domed skull in the mammoth (single dome) and the Asian elephant (twin dome) and molar characters like numerous lamellae and high degree of hypsodonty in these genera would place them side by side in morphological analysis.

Jerold Lowenstein used radioimmunoassay to compare the proteins albumin and collagen of several proboscidean genera. The technique involves reacting antisera with the protein extracts of fossil material as well as living animals. In immunological terms, the proteins from mammoths were nearly identical to those of both Asian and African elephants. Lowenstein thus concluded that Mammuthus, Elephas, and Loxodonta were equally related among themselves.

The early DNA studies gave conflicting results, with some favoring a closer relationship between Mammuthus and Loxodonta and others favoring a Mammu-thus-Elephas relationship. The most recent study on this subject (published in 2000 by Mark Thomas, Adrian Lister, and their associates) reviewed the previous data plus obtained new results from analysis of up to 545 nucleotide base pair sequences from the cytochrome b (cyt b) gene of mitochondrial DNA in the three elephant genera. While the earlier studies used sequence data from only one or two individuals each from the various genera, this study compared sequences from 5 mammoths, 14 Asian elephants, and 8 African elephants. A variety of statistical analyses turned up very similar results; Mammuthus clustered more closely with Loxodonta than it did with Elephas, although the difference was not strong. This underscored the need to use multiple lines of evidence in both morphological and molecular approaches to reconstructing phylogeny.

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