Birder's Guide

OCT 2015

Birder's Guide is the American Birding Association's newest publication. Each issue focuses on a key subject, providing tips from experienced birders on a wide variety of topics like Travel, Listing & Taxonomy, Gear, and Conservation & Community.

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Page 17 of 35

16 Birder's Guide to Listing & Taxonomy | October 2015 lthough it is fun to ima- gine the head honchos of National Geographic, Houghton Miffin Harcourt, and Knopf in a secret back- room with a giant collage of species and darts labeled Split and Lump, virtually all the recent ABA Area species name changes and changes in where to fnd species in a feld guide have been based on decisions made by the Ameri- can Ornithologists' Union's North American Checklist Committee (NACC). In turn, the NACC decisions typi- cally are based on scientifc research articles that present hypotheses concerning the evolutionary relationships of a particular group of avian taxa. These hypotheses are usu- ally presented as branching, tree-like fgures called phy- logenies. Thus, understanding phylogenies is at the heart of understanding why the names and sequences of names in our feld guides seem to be in continuous fux. This article aims to introduce birders to phylogenies, including their construction, interpretation, and application. How are phylogenies constructed? A very brief introduction to phylogenetic methods The data for constructing phylogenies primarily come from one of two sources: DNA sequences or morphology. Modern avian sys- tematics studies typically use DNA sequences for extant (or recent- ly extinct) species and reserve morphology for long-extinct species from which DNA cannot be extracted. The DNA for these studies can come from a variety of sources, including tissue, blood, feath- er, and fecal samples. Once the source sample has been obtained, the DNA is extracted in a lab (although scientists tend to use the term "extracted", the process really takes out everything but the DNA). Following extraction, researchers will prepare a sample of the DNA for sequencing, then run the prepared samples through a sequencing machine (the exact preparation technique and ma- chine will vary depending on a researcher's goal and/or resources). The end result is a set of homologous DNA sequences for each in- dividual bird in the study that can now be compared to each other via phylogenetic analyses. As with sequencing methods, analysis methods vary widely, per- haps unsurprisingly given that a set of DNA sequences to be com- pared can comprise anywhere from a few hundred to millions of data points for each sample. A description of the various methods is beyond the scope of this article, but they all compare the DNA sequences from the samples and determine the level of similarity among them. Generally, the more similar the DNA sequences, the more closely related two birds are. By generating a similarity matrix for all samples, researchers can create a nested hierarchy of proposed rela- tionships among the samples. This nested hierarchy can be presented in a number of ways, but the most common way is a phylogeny. How to read a phylogeny Figure 1 shows a hypothetical phylogeny of bird species. Be- low are explanations of various terms and features relevant to it, with each explanation matching a corresponding label on the phylogeny. A • Time: A phylogeny represents evolutionary lineages changing over time, with time progressing from the root to the tips. In this case, time progresses from left to right along the horizontal axis. B • Tip: Each tip of the tree represents a taxon of interest, often a species, at the time of its sampling. C • Node: A node represents the common ancestor of the taxa that split/descend from the node. D • Branch: A branch represents a taxon that is changing over time. E • Root: The common ancestor of all taxa represented on the tree A An Introduction Understanding and Their Taxonomy to Effects on Phylogenies The advent of using DNA sequences to help defne relation- ships among and within bird species has led to a veritable blur of taxonomic changes that often leave birders confused, frustrated, and believing in feld guide publisher conspiracies.

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