An Evolutionary Success!

Phylogenetics is the science of evolutionary relatedness.  By utilizing phylogenetic techniques, like the molecular clock, evolutionary biologists are able to pinpoint moments in time when two or more species shared a common ancestor, revealing important information about the natural history of life on Earth.  However, rarely have scientists been able to tell us the phylogenetic relatedness ‘story’ of an entire class of animals.  Surprisingly, this feat was accomplished last week as a team of evolutionary biologists created the first family tree linking all (9,993) extant bird species (Jetz et al., 2012).  These data are now able to help us understand when and where birds diversified since the Cretaceous-Paleogene (K-Pg) boundary 65 million years ago.

What did they find?

As a class birds have been around for over 150 million years.  By exploiting the aerial niche they were able to diversify and thrive and escape a competitive terrestrial landscape.  Although birds are considered to be apart of the Dinosauria clade, they outlived all other dinosaurs after the K-Pg extinction event and seem to have been successful in an evolutionary sense ever since.  Their phylogenetic tree reveals more: not only did they outlive the dinosaurs, but they also began evolving faster after the extinction of the dinosaurs.  Their species diversification rate has only continued to improve up to the present day making them one of evolution’s most successful class of animals in modern natural history.  And also making them an evolutionary conundrum since conventional wisdom in evolutionary biology was that large groups of animals diversify quickly and then slow down as fewer niches become available to exploit.

Phylogenetic trees can tell us more than just data on species diversification rates.  They can also tell us where they evolved.  This revealed another evolutionary surprise: most bird species did not evolve in the species rich tropics.  Throughout the past 50 million years most birds evolved in the western hemisphere and on islands.  Although it is still unclear why birds evolved at a faster rate in the western hemisphere, it may be because eastern hemisphere diversification was quicker before the dinosaurs went extinct, and therefore there have been more niches to exploit in the western hemisphere over the past 50 million or so years.

Either way, their high rates of diversification demands an explanation.  In my opinion it has a lot to do with flight.  Birds can exploit a niche that most other animals don’t have access to.  This enables them to travel further and adapt to changes that could easily wipe other species or classes of animals out all together.  Exploiting the aerial niche can also release birds from predation pressure and can help them avoid situations of extreme resource scarcity.  As a result, birds may be the exception to evolution’s general diversification rule.

Is it all academic?

Of course learning more about the evolutionary history of birds has an immediate practical application that can lend significant help to conservationists around the world.  By understanding specific geographic areas that have been diversification hot spots in recent natural history, conservationists can make preserving these areas a priority.  If these areas have been hot spots in the past they are likely to be important geographic areas for birds in the future.

Phylogenetic trees also raise an evolutionary problem: should conservationists focus on saving species that have more ‘unique’ evolutionary histories?  This is a problem with no clear solution but most conservationists when pinched for resources and facing the reality that all species can’t be saved tend to fall into the ‘yes’ category.  This simply means that there are species of birds that have a lot of close evolutionary cousins, and there are species that happen to be evolutionarily distinct because all of their closest relatives have gone extinct.  Conservationists tend to believe that we should try and preserve as much genetic diversity as possible and that is why evolutionarily unique species tend to get preserved over species that share a recent common ancestry with several other species.  Whether this is right or not, this recently created phylogenetic tree will give conservationists the information they need to make these decisions.

Today there are 9,993 species of birds, but 10% of them are facing extinction.  It is science like this that can provide us with the information we need to reduce that percentage and preserve a class of animals that has been thriving on our planet for over 150 million years.

References

Jetz et al.  2012.  The global diversity of birds in space and time.  Nature, doi: 10.1038/nature11631

 

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About Cadell Last
Hello. I'm probably drinking coffee and reading.

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