Evolutionary biologists have long suspected that the diversification of a species into multiple descendant species—a process known as "adaptive radiation"—stems from the adaptation of each species to different environments. However, experiments conducted to prove this hypothesis have been inconclusive due to the difficulty of establishing a definitive link between the traits of a species and the selective value of a related group that has recently branched off from a common ancestor.
Darwin's finches or Galapagos finches. Darwin, 1845.
An international team of biologists led by McGill University has collected field data for nearly two decades—studying over 3,400 Darwin's finches across the Galapagos Islands—with the aim of determining the link between the birds' beak traits and the longevity of finches from four distinct species.
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Evolution, the study is based on data from four species, all of which evolved from a common ancestor less than a million years ago. The researchers have created a detailed adaptive landscape to predict individual longevity based on beak traits. The team found that finches with beak characteristics typical of their species had greater longevity while finches with varying beak traits lived shorter lives. In an adaptive landscape, the traits of each species correspond to peaks of selective value, comparable to mountains on a topographic map, separated by valleys representing lower selective value.
"Biological species have different shapes and functions largely because individual traits, such as the beak, are determined by the environment in which the species live," explains the study's lead author, Marc-Olivier Beausoleil, a doctoral researcher at McGill University under the supervision of Professor Rowan Barrett.
Therefore, "the diversity of life results from the radiation of species, which specialize based on their environment. In the case of Darwin's finches, these environments correspond to different types of feeding," adds Professor Andrew Hendry, who has been part of the project for over 20 years.
Interestingly, the researchers also found that the studied species of finches had not yet reached the peak of their respective "adaptive peak," suggesting that each species is not perfectly adapted to its feeding type. Will evolution allow them to reach this "perfection"? Only the future will tell.
The study The fitness landscape of a community of Darwin's finches by Marc-Olivier Beausoleil et al. was published in
Evolution.