Darwin's Finches, An Iconic Adaptive Radiation

Abstract

Darwin's finches are a prime example of an adaptive radiation. Eighteen species have diversified ecologically and morphologically from a common ancestor that arrived in the Galápagos archipelago approximately 2 million years ago (Ma). Speciation occurred when populations on different islands diverged, principally in body size and beak characteristics, and continued when populations came together on a single island. Field observations show that natural selection increases the ecological differences during food scarcity caused by droughts. Genomic studies have identified two important transcription factor genes that show genetic variation associated with beak morphology. Species typically do not breed with each other, instead, they recognise and respond to members of their own species by song and appearance. Nevertheless, they do occasionally hybridise and exchange genes because the hybrids are viable and fertile. Hybridisation provides an alternative route to the formation of a new species. Key Concepts Adaptive radiation is the rapid ecological diversification of species from a common ancestor. Natural selection is the differential survival or reproduction of individuals due to differences in their phenotypic traits, and it leads to evolutionary change in the next generation if the traits are heritable. Beaks are tools for gathering and processing foods and are key functional traits in the ecological diversification of Darwin's finches. Divergence of beaks of coexisting species, known as character displacement, occurs when two species compete for a limited food supply and evolve away from each other in traits that reduce competition. Sexually reproducing species are diagnosably distinct groups that rarely if ever breed with other groups of organisms. Speciation occurs by the formation of barriers to gene exchange that may function either before mating occurs or later after fertilisation of the eggs has taken place. A premating barrier to gene exchange in Darwin's finches is formed by a sexual imprinting process whereby species‐specific song and morphology are learned early in life and used when adults choose a mate. The barrier may break down by accidental disruption of the learning process and then young finches may learn the song of another species and breed with that other species later in life. Hybrids may be viable and fertile, which results in gene flow among closely related species. Introgressive hybridisation is another route to speciation and occurs when the hybrids are sufficiently different from the parental species in song and appearance that they do not breed with them but only breed with members of their own (hybrid) group.

Spatiotemporal variations in retrovirus-host interactions among Darwin’s finches

“…The ancestor of this monophyletic group split off from the ancestral group 1–2.3 MYA 4 , during a period of climatic change with the closure of the Panamanian isthmus and the onset of the Pleistocene glaciation 5 . Adaptive radiation of the finches into a variety of ecological niches has resulted in the broad biological diversity observed today 6,7 .…”

Spatiotemporal variations in retrovirus-host interactions among Darwin’s finches

“…The ancestor of this monophyletic group split off from the ancestral group 1-2.3 MYA 4 , during a period of climatic change with the closure of the Panamanian isthmus and the onset of the Pleistocene glaciation 5 . Adaptive radiation of the finches into a variety of ecological niches has resulted in the broad biological diversity observed today 6,7 .…”