Lect_5_Morph - Integrative Biology 200A "PRINCIPLES OF...

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Integrative Biology 200A "PRINCIPLES OF PHYLOGENETICS" Spring 2008 Morphological Data I Why morphology in this day and age? Does it have any role? Some workers (e.g., Scotland, Olmstead, and Bennett, 2003) have argued that the active use of morphology in phylogenetic reconstruction is dead, and that phylogenies should be based solely on molecular data, relegating morphological characters to be passively mapped onto phylogenies later. Such an argument unwisely downplays the value of morphological characters (as being too subjectively defined and evolutionarily plastic) while conveniently forgetting that molecular characters are subject to the same uncertainties about homology and character analysis, and may be quite homoplastic as well. It is much better to take a hard look at the advantages and disadvantages of each kind of data, according to the criteria we discussed last time. First, let's start with the roles that morphological characters can play, and do the same for molecular data later. Brent's top ten reasons to include morphological characters in phylogenetics: 10. Their greater complexity may allow better homology assessments. Unlike DNA sequences, which are often one-dimensional strings (unless you have secondary structure), morphology is complex and three-dimensional, plus has ontogeny (more on that topic next time). 9. They have many potential character states . As we will see later in the semester, an important parameter determining whether your data might be subject to "long-branch attraction" problems is the number of potential character states. False reconstructions are only a problem when parallel changes to the same character state happen, a phenomenon that is most frequent with binary data and rare with many available states. 8
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This note was uploaded on 08/01/2008 for the course IB 200 taught by Professor Lindberg,mishler,will during the Spring '08 term at University of California, Berkeley.

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Lect_5_Morph - Integrative Biology 200A "PRINCIPLES OF...

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