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.
Issue link: http://bg.aba.org/i/574960
19 October 2015 | Birder's Guide to Listing & Taxonomy lists). If two populations within a species of bird show signifcant differences in plum- age, ecology, and/or vocalizations, and they are each monophyletic, then proposals to split the species usually succeed. If the same differences between populations are pres- ent but the two populations are not each monophyletic (i.e., a phylogeny of the spe- cies shows members of the two populations mixed together within a clade), then the two populations usually remain lumped. I say "usually" for both scenarios because all species-level decisions are still subject to the personal opinions of taxonomic com- mittee members and the members' applica- tion of species concepts. (For more on this topic, plus a glossary defning many terms used in this article, see Morgan Churchill's article in the 2014 issue of Birder's Guide to Listing & Taxonomy.) Although phylogenies are relatively objective, the taxonomic deci- sions based on them are not. Lest I make it sound like phylogenies are a completely objective, end-all solution to taxonomic problems, I want to reiterate that phylogenies are hypotheses. No phylog- eny is a fact, even if one may sometimes be presented as such by overenthusiastic folks. Just as with any scientifc hypothesis, some phylogenies may be better supported than others. Do all gene sequences produce the same tree? Do all nodes in the phylog- eny have very high support values? If not, then it's a good sign that a particular phy- logeny may not be very well-supported, a very important consideration when making taxonomic decisions. Even seemingly well- supported phylogenies have turned out to be incorrect after more data were added. Thus, even with a tree with high node sup- port values in hand, taxonomists may still hesitate to pull the trigger on that split (i.e., lifer!) we've all eagerly anticipated until a study using a different set of data produces the same results. Aside from our life lists, phylogenies also affect what order species are presented in most feld guides. Species tend to be pre- sented in taxonomic order, theoretically to inform users about evolutionary relation- ships. But what is taxonomic order? The linear order of taxa in a particular phylog- eny. Phylogenies tend to be presented in such a way that the longer of two branches extending forward from a node always goes on the same side of the node, so the linear arrangement of taxa is not completely arbi- trary. Therefore, when nodes move around in an updated phylogenies, taxonomic or- der usually changes as well. However, if you'll permit me a moment on the soapbox, I think feld guides should stop using taxonomic order to organize families and/or orders. As I discussed ear- lier, the linear order of taxa is a very unreli- able way to communicate evolutionary re- latedness. Any node in a phylogeny can be rotated, making it possible to create a very wide range of linear orders that all refect the same evolutionary relationships. Thus, if the point of changing the order of families and/orders is to inform birders of evolution- ary relationships, which I believe it is, then it is a very fawed way to present this in- formation. As an example, the current taxo- nomic order of feld guides (and the AOU Check-list) presents us with grouses, loons, grebes, and famingos (in that order) near the front and blackbirds near the very back. Previously, the order was loons and grebes at the front, famingos a little later, grouses a little later, and blackbirds still near the end. But what does the updated order tell us about the evolutionary relationships among these fve groups? Virtually nothing intuitive (or correct; see Figure 2)! Would we have guessed that loons are more closely related to blackbirds than they are to grouse? Or that famingos and grebes were each other's closest relatives and not very closely related to loons at all? Without outside information, I doubt that I would have. Instead of changing the taxonomic order as a poor proxy for conveying updated evo- lutionary information, use a phylogeny! Es- tablish a standard family/order sequence in feld guides, and add a phylogeny of these taxa to the introduction section. Thus, evo- lutionary relationships can be updated in the phylogeny section, but ease of use can be relatively stable when looking for a bird in a new feld guide edition. I look forward to phylogenies becoming a standard part of a feld guide's introduction; we could all use some more tree-thinking in our lives! References Jarvis, E.D., S. Mirarab, A.J. Aberer, B. Li, P. Houde, C. Li,… G. Zhang. 2014. Whole- genome analyses resolve early branches in the tree of life of modern birds. Science 346: 1320–1331. McGuire, J.A., C.C. Witt, D.L. Altshuler, & J.V. Remsen, Jr. 2007. Phylogenetic systemat- ics and biogeography of hummingbirds: Bayesian and maximum likelihood analyses of partitioned data and selection of an ap- propriate partitioning strategy. Systematic Biology 56: 837–856. McGuire, J.A., C.C. Witt, J.V. Remsen, Jr., R. Dud- ley, & D.L. Altshuler. 2009. A higher-level taxonomy for hummingbirds. Journal of Or- nithology 150:155–165. McGuire, J.A., C.C. Witt, J.V. Remsen, Jr., A. Corl, D.L. Rabosky, D.L. Altshuler, & R. Dudley. 2014. Molecular phylogenetics and the di- versifcation of hummingbirds. Current Biol- ogy 24:910–916. Allen's Hummingbird Selasphorus sasin Calliope Hummingbird Selasphorus calliope Rufous Hummingbird Selasphorus rufus Broad-tailed Hummingbird Selasphorus platycercus Anna's Hummingbird Calypte anna Figure 4. Adapted from McGuire et al. (2014), this phylogeny shows the relationships among a subset of the Selasphorus hummingbirds, illustrating that Calliope Hummingbird is embedded within the genus and must be included in it to render Selasphorus monophyletic.