Darwin’s finches are among the most celebrated examples of adaptive radiation in the evolution of modern vertebrates and now a new study, led by scientists from the University of Bristol, has provided fresh insights into their rapid development and evolutionary success.
Study of the finches has been relevant since the journeys of the HMS Beagle in the 18th century which catalysed some of the first ideas about natural selection in the mind of a young Charles Darwin.
Despite many years of research which has led to a detailed understanding of the biology of these perching birds, including impressive decades-long studies in natural populations, there are still unanswered questions.
Specifically, the factors explaining why this particular group of birds evolved to be much more diverse in species and shapes than other birds evolving alongside them in Galapagos and Cocos islands have remained largely unknown.
A similar phenomenon is that of the honeycreepers endemic to the Hawaiian archipelago. These true finches (unlike Darwin’s finches which are finch-like birds belonging to a different family) radiated to achieve an order of magnitude more in species and shapes than the rest of the birds inhabiting those islands.
An international team of researchers from the UK and Spain tackled the question of why the rapid evolution in these birds from a different perspective.
They showed in their study published today in the journal Nature Ecology & Evolution that one of the key factors related to the evolutionary success of Darwin’s finches and Hawaiian honeycreepers might lie in how their beaks and skulls evolved.
Previous studies have demonstrated a tight link between the shapes and sizes of the beak and the feeding habits in both groups, which suggests that adaptation by natural selection to the different feeding resources available at the islands may have been one of the main processes driving their explosive evolution.
Furthermore, changes in beak size and shape have been observed in natural populations of Darwin’s finches as a response to variations in feeding resources, strengthening these views.
However, recent studies on other groups of birds, some of which stem from the previous recent research of the team, have suggested that this strong match between beak and cranial morphology and ecology might not be pervasive in all birds.
Professor Emily Rayfield, from the University of Bristol’s School of Earth Sciences, co-authored the new study. She said: “Other factors such as constraints on skull shape during development, the use of the beak for many other functions and the fact that the skull and beak develop and function as a coherent unit may have contributed to this mismatch.
“Therefore, the strong connection between beak, cranial morphology and feeding ecology over the evolution of Darwin’s finches, Hawaiian honeycreepers, and perhaps other lineages of birds, might have been only possible if this tight coevolution of cranial regions is somehow ‘relaxed’ and those regions are able to evolve more freely.”
