EVOLUTION ON ISLANDS

Evolution in island birds: testing patterns and investigating mechanisms

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 Obiettivo del progetto (Objective)

'Species on islands are widely believed to undergo similar evolutionary changes as an adaptation to the island environment, a process referred to as the ‘island syndrome’. These changes affect morphological, reproductive, physiological and behavioural traits such as sexual selection. Evolutionary change on islands is believed to relate to genetic (e.g. bottleneck) and ecological factors (e.g. release from natural enemies such as parasites and predators). However, very few broad-scale tests of these patterns have been conducted and few detailed studies examined the underlying processes. Additionally, previous studies were mostly based on data obtained from the literature, which are typically variable in quality. This is surprising given the central role of islands in ecological and evolutionary theory. Whether an ‘island syndrome’ does exist or not can only be established by demonstrating that a set of traits has arisen independently several times in unrelated taxa and geographically distinct areas. We propose to examine whether there are consistent patterns of adaptation in morphological, reproductive and sexually selected traits of island birds worldwide and to investigate some of the underlying causes. To this end, we will first collect standardised data from museum specimens for islands and nearby mainland areas from around the world consisting of morphological, egg and plumage colour measures. Subsequently, we will investigate in detail some of the underlying processes and consequences of evolutionary change on islands in the Gulf of Guinea using weaver (Aves, Ploceidae) species, for which phylogeographic data is available, on the island of São Tomé and nearby mainland Gabon. Specifically, we will address the interaction between decreased parasite pressure, immunity, intensity of sexual selection and reproductive investment to elucidate some of the constraints and trade-offs that lead to changes on islands.'

Introduzione (Teaser)

Many bird species on remote islands have been developing quite differently from their equivalents on the mainland. One EU project looked at the mechanisms behind this bifurcating evolution and the curious differences at play.

Descrizione progetto (Article)

Animal life on the islands often evolves separately from the same species on the mainland, offering fascinating insight into how they adapt in isolated environments. The EU-funded project 'Evolution in island birds: testing patterns and investigating mechanisms' (Evolution ON Islands) studied the evolutionary mechanisms and adaptations in the bird family.

The researchers tested how birds adapted to island environments on a global scale, which involved a joint initiative among three European countries. They found that birds' behaviour, characteristics and reproductive capabilities the world over often evolved in a similar matter on different islands, an intriguing phenomenon referred to as 'island syndrome'. Morphological changes saw bird evolution repeatedly lead to flightlessness, accompanied by changes in feeding habits, body size and bill structure.

By studying island specimens in museums, the project was able to build a database of more than 240 species cataloguing size, shape, egg traits, plumage colour and other data. It showed that island species generally have reduced colouration, less fancy patches and duller feathers, hinting at decreased sexual traits and morphology.

The project also applied the 'island rule' for mammals on birds. The rule stipulates that generally large animals tend to become smaller on the islands, while the opposite is true as well. The project also found that in temperate island regions (yet not in tropical ones) animals are less fertile, boasting longer developmental periods and paying more attention to the young.

Evolution ON Islands then investigated the factors behind the patterns of adaptation observed. It researched the adaptive basis of cooperative breeding in specific bird species, in addition to studying if insular bird species on islands experience lower parasite pressures than their mainland counterparts.

Project scientists have published several papers and manuscripts on the subject which have raised some highly interesting facts about the bird world.