Use of Biometrics in Animal Taxonomy
EXERCISE 7
Use of Biometrics in Animal Taxonomy
ANSWERS TO STUDY QUESTIONS:
1. Discuss the conflict between the uses of molecular markers against morphological characters in the construction of phylogenetic trees.
Molecular phylogenetics predates DNA sequencing by several decades. It is derived from the traditional method for classifying organisms according to their similarities and differences (morphological characters), as first practiced in a comprehensive fashion by Linnaeus in the 18th century. However, whether the objective is to construct a classification or to infer a phylogeny, the relevant data are obtained by examining variable characters in the organisms being compared. Originally, these characters were morphological features, but molecular data were introduced at a surprisingly early stage. In 1904, Nuttall's work showed that molecular data can be used in phylogenetics, but the approach was not widely adopted until the late 1950s. These changes came about with the introduction of phenetics and cladistics, two novel phylogenetic methods which, although quite different in their approach, both place emphasis on large datasets that can be analyzed by rigorous mathematical procedures. The difficulty in obtaining large mathematical datasets when morphological characters are used was one of the main driving forces behind the gradual shift towards molecular data, which have three advantages compared with other types of phylogenetic information. First, when molecular data are used, a single experiment can provide information on many different characters: in a DNA sequence, for example, every nucleotide position is a character with four character states, A, C, G and T. Large molecular datasets can therefore be generated relatively quickly. Second, molecular character states are unambiguous: A, C, G and T are easily recognizable and one cannot be confused with another. Some morphological characters, such as those based on the shape of a
Use of Biometrics in Animal Taxonomy
ANSWERS TO STUDY QUESTIONS:
1. Discuss the conflict between the uses of molecular markers against morphological characters in the construction of phylogenetic trees.
Molecular phylogenetics predates DNA sequencing by several decades. It is derived from the traditional method for classifying organisms according to their similarities and differences (morphological characters), as first practiced in a comprehensive fashion by Linnaeus in the 18th century. However, whether the objective is to construct a classification or to infer a phylogeny, the relevant data are obtained by examining variable characters in the organisms being compared. Originally, these characters were morphological features, but molecular data were introduced at a surprisingly early stage. In 1904, Nuttall's work showed that molecular data can be used in phylogenetics, but the approach was not widely adopted until the late 1950s. These changes came about with the introduction of phenetics and cladistics, two novel phylogenetic methods which, although quite different in their approach, both place emphasis on large datasets that can be analyzed by rigorous mathematical procedures. The difficulty in obtaining large mathematical datasets when morphological characters are used was one of the main driving forces behind the gradual shift towards molecular data, which have three advantages compared with other types of phylogenetic information. First, when molecular data are used, a single experiment can provide information on many different characters: in a DNA sequence, for example, every nucleotide position is a character with four character states, A, C, G and T. Large molecular datasets can therefore be generated relatively quickly. Second, molecular character states are unambiguous: A, C, G and T are easily recognizable and one cannot be confused with another. Some morphological characters, such as those based on the shape of a