Tree of Death: Do Close Relatives Become Extinct Together?

Conservation biologists may be able to rely on a molecular phylogeny as an early warning for poorly known species because if those species’s close relatives are already endangered, they too may be at risk of decline in the future

by GrrlScientist for ScienceBlogs | @GrrlScientist

An adult male Eurasian blackbird (Turdus merula). (Credit: CC BY-SA 3.0Β [view].)

A paper recently published by British scientist, Gavin Thomas, a population biologist at Imperial College London, finds that British bird species that currently are suffering population declines tend to be close relatives. The reason would appear to be obvious: closely related species tend to share many traits, such as very precise habitat requirements, and what’s bad for one species is similarly bad for its closest relatives. However, the habits and needs of some species are poorly known, so this study suggests that conservationists could rely on genetic relatedness to predict future population declines and extinctions, even for relatively unknown species.
β€œNumbers of the common blackbird are currently not perceived as threatened at all, however it has several close relatives, including the song thrush, that are experiencing severe levels of population decline,” observes Dr. Thomas, whose paper was just published in the Royal Society’s Proceedings B journal. β€œThis could mean that populations of blackbirds in the UK are at risk of declining in the future.”

Using this same hypothesis, the European greenfinch, Carduelis chloris, might also be vulnerable to a population decline in the near future because its close relatives, linnets and bullfinches, are currently experiencing severe population declines.

European greenfinch, Carduelis chloris, in the harsh autumn morning light, eating the last berries of autumn in Helsinki, Finland. (Credit: Thermos / CC BY-SA 2.5Β [view].)

But this hypothesis requires closer examination and rigorous testing before it can be relied upon as a predictive tool in conservation biology.

β€œThis hasn’t been tested on the ground, so we don’t know at the moment whether the inferences we’re making turn out to be true,” Dr. Thomas cautioned.

Thomas’s phylogeny, or family tree, is derived from mitochondrial sequence data for 248 species of British bird species that he retrieved from GenBank and analyzed using a relaxed clock Bayesian inference method (Figure 1).

Figure 1: A phylogeny of British birds. The phylogeny is the maximum credibility tree from the posterior distribution of trees. Nodes marked with a filled circle contain species that were constrained to be monophyletic a priori. Nodes with posterior probabilities less than 50% are collapsed to polytomies. Species marked with asterisks are species for which non-British congeners were used as surrogates. (doi:10.1098/rspb.2008.0549 [view].)

In addition to its predictive conservation potential, this phylogeny is also important because it documents evolutionary relationships between 93 percent of all sedentary and migratory British bird species.

β€œPulling together the family tree was an important task as we now have a clearer insight than ever before into the evolutionary relationships of birds in Britain,” adds Dr. Thomas.

This study suggests that conservationists might be able to rely on a molecular phylogeny as an early warning device for poorly known species because if those species’ close relatives are already endangered, they too may be at risk of decline in the future.

β€œThe data clearly shows a link between closely related birds and chances of population decline which could be useful for conservationists, although they will always need to take other factors, such as range contraction, into account,” advises Dr. Thomas.


Thomas, G.H. (2008). Phylogenetic distributions of British birds of conservation concern, Proceedings of the Royal Society B: Biological Sciences, doi:10.1098/rspb.2008.0549

Originally published at on 19 June 2008.