Macroevolutionary Speciation Rates are Decoupled from the Evolution of Intrinsic Reproductive Isolation in Drosophila and Birds

Rabosky D.L., Matute D.R. 2013. Macroevolutionary speciation rates are decoupled from the evolution of intrinsic reproductive isolation in Drosophila and birds. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1305529110.

This Daniel-and-Daniel production addresses a long-standing issue regarding the suspected correlation between diversification rates and factors that promote (or inhibit) intrinsic reproductive isolation. As the title suggests, Daniel and Daniel found no correlation between speciation rates and the evolution of intrinsic reproductive isolation in fruit flies (Drosophila) and birds. The novelty of this paper comes in two forms, depending on from which branch of science you hail; either A) the conclusion that Drosophila and birds diversify at rates independent of factors associated with reproductive isolation (such as geographic isolation, lineage-specific extinction rates, etc.) surprises you, or B) you recognize the novelty in that Rabosky and Matute were the first to empirically test a long-standing hypothesis with a large (empirical) dataset. To many of us who think about ecological speciation, divergence in allopatry, or organisms outside of a lab setting, point (A) is not necessarily a surprise, but it is good to know that past suppositions hold water when tested with empirical data.

Participants of our seminar came up with a number of questions that would be helpful to know when interpreting their results. Some of these questions are:
1) How does having a lot of anatid (duck and goose) samples bias the bird results, since they are known to hybridize so much?
2) How does avian taxonomy and the propensity to split species, even into different genera, affect the results (mostly for Price 2002 study that these results were based upon)?
3) How was psi (the lineage-specific rate of the evolution of reproductive isolation) calculated?

Overall, everyone enjoyed the paper, but had concerns regarding the bird data, whereas the Drosophila data were much stronger. Of course, any study has to overcome the problem of small sample sizes, but a study like this still makes you wonder: how are speciation rates related to the evolution of reproductive isolation in other taxa?
[UW phylogenetics seminar, 10/17/2013, Jared Grummer]

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