Darwin's finches: How one species becomes many

The complex puzzle of how one species evolves into many has been a subject of fascination and study for evolutionary biologists for decades. 

A recent study from McGill University has shed new light on this enigma through an extensive study of Darwin’s finches in the Galápagos Islands.

Study significance 

Over nearly two decades, the team collected and analyzed data from more than 3,400 individual finches spanning four different species. 

The research has been pivotal in establishing a clear relationship between specific beak traits and the longevity of these birds. The study also offers new insights into the mechanisms of species adaptation and survival.

Adaptive radiation 

Adaptive radiation is a process where a single species evolves into multiple descendant species, each adapted to a unique environment. While this is a fundamental theory in evolutionary biology, empirical evidence to support this theory has been challenging to obtain. 

“The drivers of adaptive radiation have often been conceptualized through the concept of ‘adaptive landscapes,’ yet formal empirical estimates of adaptive landscapes for natural adaptive radiations have proven elusive,” wrote the study authors. 

Darwin’s finches 

The McGill team focused on Darwin’s finches, a classic example of adaptive radiation. 

“Darwin’s finches started to radiate on the Galápagos about 1.5 million years ago; however, radiation of the ground finch (Geospiza) group was more rapid and recent, perhaps starting between 100,000 and 400,000 years ago. The primary phenotypic driver of this radiation at all phylogenetic levels is thought to be variation in beak (and body) size and shape,” wrote the study authors.

Beak traits 

For their investigation, the researchers constructed a detailed “fitness landscape.” This landscape helped predict an individual finch’s longevity based on its beak traits. 

“Biological species are diverse in their shape and functions mainly because individual traits, such as beaks, are selected by the environment in which the species are found,” explained study lead author Marc-Olivier Beausoleil, a doctoral researcher at McGill.

The experts discovered that finches with beak traits typical of their species enjoyed higher survival rates, whereas those deviating from these traits had lower survival rates.

Fitness landscape 

According to the researchers, the traits of each species correspond to fitness peaks that can be compared to mountains on a topographic map separated from other mountains by valleys of lower fitness.

As a result, “the diversity of life is a product of the radiation of species to specialize on different environments; in the case of Darwin’s finches, those environments are different food types,” explained Professor Andrew Hendry, who has been a part of the project for more than 20 years.

An intriguing aspect of the study’s findings is that the finch species have not yet reached the pinnacle of their fitness “mountains.” This observation implies that these species are not perfectly adapted to their respective food types, leaving open the question of whether such perfection in adaptation is attainable.

The study is published in the journal Evolution.

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