All living organisms are tips of an evolutionary tree that emerged over 3.5 billion years from a single common ancestor. Research in the Department of Bionanoscience at Delft University of Technology has provided the first experimental demonstration that the rate at which this tree branches depends on the ecological versatility of the ancestors. The study was published in the scientific journal PNAS.
One important mechanism by which the evolutionary tree of life branches into new species is adaptive radiation: rapid evolution of different species from a single common ancestor. Darwin's finches are a famous example of this. In the nineteenth century, Darwin was the first to conclude that the finches of the Galapagos Islands had originated from a single common ancestor. But what determines the course of adaptive radiation?
There was already experimental evidence that showed that the dynamics of adaptive radiation are influenced by environmental factors. 'But evolutionary theory also predicts that the ecological characteristics of the ancestor should play a role,' explains Dr Bertus Beaumont (Kavli Institute of Nanoscience; Dept. of Bionanoscience). 'In order to examine this experimentally for Darwin's finches, one would have to travel three million years back in time. For this reason, we examined the prediction by studying adaptive radiation in experimental populations of bacteria. Owing to their short generation time, bacterial evolution can be studied in real time.'
Beaumont and his PhD students Régis Flohr and Carsten Blom alterred the ecological behaviour of the ancestor and examined the impact of these changes on their ability to diversify by adaptive radiation. 'There was indeed a connection. New types of bacteria evolved less rapidly from ancestors with a broad, non-specialist survival strategy (i.e., those occupying a broad ecological 'niche'). These ecological 'jacks-of-all-trades' thus delayed branching of the evolutionary tree." Their evolutionary experiment provided the first experimental demonstration that the ecological niche of the ancestor constrains the rate of adaptive radiation.
'This result supports and important component of evolutionary theory. At the same time, it reveals a mechanism that can increase the impact of chance on evolution. The organisms that encounter the opportunity to undergo adaptive radiation are determined in part by chance, and with that also the ecological niche of the prospective founder, which may affect the rate of diversification' argues Beaumont. The mechanism that we have observed may have reduced the predictability of evolution.'
According to Beaumont, the work advances our understanding of the evolution of biodiversity and provides a method to quantify evolutionary diversification of micro-organisms. This is essential for understanding and controlling microbial populations in nature (e.g. the evolution of antibiotic-resistant bacteria) and in biotechnology (e.g. wastewater treatment). In addition, the research paves the way for the study of evolutionary diversification of micro-organisms with nanofluidic chips, an application of nanotechnology that will make it possible to unravel much more complex evolutionary patterns greater detail.
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More information: Founder niche constrains evolutionary adaptive radiation.Flohr RC, Blom CJ, Rainey PB, Beaumont HJ. Proc Natl Acad Sci U S A. 2013 Dec 4.