Species delimitation in birds (1 Viewer)

[Peter Kovalik]

Carlos Daniel Cadena, Felipe Zapata, The genomic revolution and species delimitation in birds (and other organisms): Why phenotypes should not be overlooked, Ornithology, 2021;, ukaa069, https://doi.org/10.1093/ornithology/ukaa069

Abstract:

Given the availability of genomic data to identify separately evolving groups of organisms, many researchers establish species limits based on assessments of the extent of gene flow among populations and often use analytical approaches to identify species in which gene flow is explicitly disallowed. Strictly considering lack of—or limited—gene flow as the main or only criterion to delimit species involves two main complications in practice. First, approaches often used to analyze genome-wide data cannot by themselves distinguish species limits from within-species population structure, particularly in allopatric organisms. Second, recognizing as species only those lineages one can identify using such approaches fails to embrace the role of other evolutionary forces (i.e. various forms of selection) in defining evolutionary lineages. Using examples from various groups of birds, we call for the importance of considering evolutionary forces additional to gene flow in species delimitation and explain why genomic approaches commonly used in taxonomic studies may be insufficient by themselves to properly uncover species limits. By considering the processes that structure genotypic and phenotypic variation during speciation, we argue that rigorous analyses of phenotypic variation remain crucial for species delimitation in the genomics era because phenotypes uniquely inform us about the role of selection maintaining the cohesion of evolutionary lineages. Evolutionary theory describing the roles of gene flow, genetic drift and natural and sexual selection in the origin and maintenance of species calls for an integration of genomics with phenomics in avian species delimitation.

 

[Mysticete]

I don't know if people are still following the German bird phylogeny, but there have been a few updates, this being the most recent one:

"Species delimitation"

Guided by the idea that DNA is informative at all taxonomic levels, the delimitation of species and subspecies should be based on divergence times (as recommended for allopatric forms by Price, 2008 and Hudson & Price, 2014; but see Winkler, 2021). For example, species status might be attributed...

www.bird-phylogeny.de

Where he argues that species should be recognized for anything that diverged 2 million years ago, and subspecies at 1 million. This sort of feels like a situation where everything is a nail when your only tool is a hammer. In this case the author extending the idea of using divergent dates to decide all classification questions.

In this case, this sort of criteria seems unworkable, since I don't think we have that many population level divergence dates, and I don't know how you calibrate your dates at this level. My guess is this would basically toss out all subspecies and lead to a mass lumping the extent of which would probably send crowds of birders with pitchforks to his door

I do think age of divergence is useful in looking at speciation, but not the end all, be all.

 

[jts1882]

I think it's useful to push these ideas to the limit to see how it works out. It should provide some insight into how age criteria can be applied. But any attempt to be dogmatic/idealistic will be doomed to fail.

The new Dubois amphibian taxonomy is an example of a system pushed to the limit. It's extremely unlikely to get widely adopted, but is quite informative and interesting.