Speciation and Biogeography of Birds, The

Auk, The, Oct 2004 by Zink, Robert M, Jones, Andrew W

The Speciation and Biogeography of Birds.-Ian Newton. 2003. Academic Press, Amsterdam, xii 668 pp. ISBN 0-12-517375-X. Cloth, $75.00.-Thanks to advances in phylogenetic methods and molecular systematics, the fields of speciation and biogeography have advanced at a tremendous pace. For a researcher entering this field, the literature presents a formidable challenge, and a synthesis of research in biogeography and speciation has been sorely needed. Ian Newton's book, The Speciation and Biogeography of Birds, is an awkward step in this direction. Part of the awkwardness comes from confusion as to what the book is actually about. The book traverses a large number of issues, from the role of humans in causing extinctions, productivity of marine environments, dry-wet cycles, glaciation, ecological issues (habitat, food, predators, parasites, competition), and migration, to the molecular clock, to mention a few. After reading the book, it is clear that it is not about speciation or historical biogeography; instead, it is a book about ecological biogeography. The lasting contribution of the book is in its summary of avian distributions and natural history, not in the phylogenetic interpretation of speciation and biogeography.

The fields of speciation and biogeography are inherently rooted in phylogenetic reasoning. However, this is not Newton's main area of expertise, which renders some of the sections in Part 1, which focus on "Evolution and Diversity of Birds" misleading. In particular, the sections are grounded in the school of "evolutionary systematics" (e.g. Mayr and Ashlock 1990), which is not the paradigm used by the majority of modern systematists. Thus, we cannot recommend those sections as a general introduction for a student of ornithology or evolution. Newton prefers the Biological Species Concept for its "recognition" of varying levels of diversity, such as superspecies, subspecies, and allospecies. Newton views those taxonomic categories as objective and uses them as a basis for his analyses. However, the monophyly of few of those taxa have been corroborated by phylogenetic analysis, rendering them potentially inappropriate for his intended use. Newton notes that morphological assessments of evolutionary relationships can be compromised by convergence and that DNA characters are potentially more objective. Convergence is indeed a problem with morphological data, but phylogenetic (cladistic) methods are much better able to detect it than the evolutionary systematics that Newton favors. However, Newton also states that molecular phylogenies and molecular clocks might not be trusted because of many untested assumptions. Although certainly true in some cases, it is the morphological assessments-mostly subjective, non-character-based, and precladistic-that are equally, if not more, suspect. Thus, strengths and weaknesses of different types of data and methods of phylogeny reconstruction are riot clearly presented. Perhaps not surprisingly, in the entire book, there are only three phylogenetic trees, the most recent of which was published in 1996.

There are several other problems with the treatment of molecular systematics. Newton equates taxonomic rank with genetic distance rather than tree topology. He states that DNA-DNA hybridization is important for "resolution of the older branches" in the avian tree; however, we know of no lab that still uses DNA-DNA hybridization for phylogenetic inference, because it is recognized that sequence analysis is preferable for all depths in the avian tree of life. Newton repeats (p. 500) the common misperception in the literature that microsatellites evolve more rapidly than mtDNA because of a higher mutation rate. It is indeed a result of Kimura's neutral theory that for strictly neutral traits, the fixation rate equals the mutation rate, independent of the population size. However, this is for loci in the same genome. The confusion stems from misunderstanding of "evolve more rapidly." Although some microsatellite loci have high mutation rates and hence many alleles, it does not follow that those loci have a better chance of capturing population isolation than an mtDNA gene tree. The nuclear genome, because of its mode of inheritance, coalesces on average of four times more slowly than does the mtDNA genome.

Several other problems are worth noting. In comparing the number of species in sister clades, Newton states (p. 350) that the clade with the highest number of species "...has diversified at a faster rate." Slowinski and Guyer (1989) showed that there could be a huge discrepancy in the number of species in sister clades by chance. Without a statistical test of a clear null model, current clade diversity is not necessarily a predictor of speciation rate. The literature on relative range overlaps of sister species, as a means of inferring the geographic mode of speciation, is not dealt with. The lack of discussion of the importance of coalescence theory in phylogeography is also a shortcoming of the book.