Final Report Summary - EVOLUTION ON ISLANDS (Evolution in island birds: testing patterns and investigating mechanisms)
This fellowship was set to last two years, but terminated at the end of September 2009 because I was offered a 5-year research position in Portugal. The scientific work plan in the project proposal consisted of two parts that were planned to last approximately one year each. The first part was a test of global patterns of adaptation in island birds based on museum specimens and the literature. We successfully accomplished this first part of the project. The work conducted so far has lead us to set up a new collaborative project between three European countries to investigate the factors underlying the insularity patterns uncovered and we have applied for funding from the Portuguese Science Foundation to conduct this work.
Part 1: Testing global patterns of island adaptation and underlying processes
A number of empirical and theoretical studies suggest that species on islands worldwide frequently undergo similar evolutionary changes as a process of adaptation to the island environment, a process often referred to as the 'island syndrome'. These changes are believed to affect morphological, reproductive, physiological and behavioural traits. In birds, morphological changes are believed to include the repeated evolution of flightlessness and changes in bill and body size related to shifts in feeding ecology. Recent evidence also suggests a decrease in intensity of sexual selection, with associated changes in sexually selected traits. However, very few broad-scale tests of these patterns have been conducted. Additionally, previous studies were usually based on data obtained from the literature. This is problematic since these data are typically variable in quality, are often obtained through different methodologies and can be based on reduced sample sizes. 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.
Secondary sexual traits and morphology
Since 2008 we have been collecting standardised data from museum specimens from islands and nearby mainland areas from around the world; we have now gathered a data-base of over 240 species. Data collected consists of morphological (bill and body size and shape), egg (size and colour) and plumage colour (brightness, chroma, hue and size of patches) measures for island species and their closest mainland relatives.
Using statistical analyses based on paired comparisons matched for phylogeny and latitude, we found that island species usually have reduced colouration. Specifically, there is a decrease in the number of coloured patches, number of colours and plumage brightness. These data were used in two MSc thesis and a manuscript reporting these initial results is currently in preparation. In addition we set up a collaboration between Portuguese, French and Swedish and have applied for funding in order to investigate some of the possible factors underlying the observed decrease in sexual ornaments on islands.
Additional analyses of this data-set are investigating patterns of morphological change on islands, in particular to provide a test of the 'island rule' in birds. According to this rule, large animals tend to become smaller on islands, while small ones tend to get bigger. Initially demonstrated for mammals, this hypothesis has become controversial after recent studies on lizards and also mammals, but little is known for birds.
The egg data collected (egg size and colouration) is insufficient to conduct conclusive analyses and therefore we applied for funding to visit the Western Foundation of Vertebrate Zoology in order to complete our sampling and conclude the analyses.
Life history
Theory suggests that island faunas have reduced fecundity, longer developmental periods and increased investment in young. However, no broad-scale test of these patterns has ever been conducted. Additionally, given marked latitudinal differences in life-history, reproductive adaptations to insular environments might differ in tropical and temperate regions. I have collated a literature-based data-set to examine life-history patterns of adaptation world-wide using island-mainland pairs of birds matched for latitude and phylogeny and examine differences within regions. I found:
1) reduced fecundity on islands in temperate, but not tropical regions;
2) larger egg volume on tropical islands, but not on temperate ones;
3) a global pattern of longer developmental periods on islands; and
4) no differences in parental care and mating system.
Analyses of nesting success suggested that these results were unrelated to lower nest predation on islands. Instead, the differences found between tropical and temperate regions suggest the island effect relates to environmental stability and adult survival. A manuscript reporting these results is currently in review.
Part 2: Unravelling the mechanisms of adaptation
This second part of the project was a planned to be a field-based investigation of the factors underlying the patterns of adaptation revealed in the first part of the study. We did not complete this since the fellowship had to be terminated at the end of the first year because R. Covas was offered a five-year position in Portugal that started in October 2009. However, we are still going to pursue his project in collaboration with French, Swedish and Portuguese colleagues.
Other research activities
During the period covered by the fellowship, I carried on conducting research on a long-term project with which I have been involved for several years that investigates the adaptive basis of cooperative breeding in the sociable weaver Philetairus socius, an African passerine. During the duration of this Marie Curie fellowship I worked on two manuscripts, on of each is now published.
In addition, I continued work initiated previously on island parasites in the Gulf of Guinea. This project aims to determine whether insular bird species in these islands experience lower parasite pressures than their mainland counterparts and was done in collaboration with R. Fleischer and J. Beadell (Smithsonian Institute, Washington, USA). During this period we published one paper on the topic.
Part 1: Testing global patterns of island adaptation and underlying processes
A number of empirical and theoretical studies suggest that species on islands worldwide frequently undergo similar evolutionary changes as a process of adaptation to the island environment, a process often referred to as the 'island syndrome'. These changes are believed to affect morphological, reproductive, physiological and behavioural traits. In birds, morphological changes are believed to include the repeated evolution of flightlessness and changes in bill and body size related to shifts in feeding ecology. Recent evidence also suggests a decrease in intensity of sexual selection, with associated changes in sexually selected traits. However, very few broad-scale tests of these patterns have been conducted. Additionally, previous studies were usually based on data obtained from the literature. This is problematic since these data are typically variable in quality, are often obtained through different methodologies and can be based on reduced sample sizes. 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.
Secondary sexual traits and morphology
Since 2008 we have been collecting standardised data from museum specimens from islands and nearby mainland areas from around the world; we have now gathered a data-base of over 240 species. Data collected consists of morphological (bill and body size and shape), egg (size and colour) and plumage colour (brightness, chroma, hue and size of patches) measures for island species and their closest mainland relatives.
Using statistical analyses based on paired comparisons matched for phylogeny and latitude, we found that island species usually have reduced colouration. Specifically, there is a decrease in the number of coloured patches, number of colours and plumage brightness. These data were used in two MSc thesis and a manuscript reporting these initial results is currently in preparation. In addition we set up a collaboration between Portuguese, French and Swedish and have applied for funding in order to investigate some of the possible factors underlying the observed decrease in sexual ornaments on islands.
Additional analyses of this data-set are investigating patterns of morphological change on islands, in particular to provide a test of the 'island rule' in birds. According to this rule, large animals tend to become smaller on islands, while small ones tend to get bigger. Initially demonstrated for mammals, this hypothesis has become controversial after recent studies on lizards and also mammals, but little is known for birds.
The egg data collected (egg size and colouration) is insufficient to conduct conclusive analyses and therefore we applied for funding to visit the Western Foundation of Vertebrate Zoology in order to complete our sampling and conclude the analyses.
Life history
Theory suggests that island faunas have reduced fecundity, longer developmental periods and increased investment in young. However, no broad-scale test of these patterns has ever been conducted. Additionally, given marked latitudinal differences in life-history, reproductive adaptations to insular environments might differ in tropical and temperate regions. I have collated a literature-based data-set to examine life-history patterns of adaptation world-wide using island-mainland pairs of birds matched for latitude and phylogeny and examine differences within regions. I found:
1) reduced fecundity on islands in temperate, but not tropical regions;
2) larger egg volume on tropical islands, but not on temperate ones;
3) a global pattern of longer developmental periods on islands; and
4) no differences in parental care and mating system.
Analyses of nesting success suggested that these results were unrelated to lower nest predation on islands. Instead, the differences found between tropical and temperate regions suggest the island effect relates to environmental stability and adult survival. A manuscript reporting these results is currently in review.
Part 2: Unravelling the mechanisms of adaptation
This second part of the project was a planned to be a field-based investigation of the factors underlying the patterns of adaptation revealed in the first part of the study. We did not complete this since the fellowship had to be terminated at the end of the first year because R. Covas was offered a five-year position in Portugal that started in October 2009. However, we are still going to pursue his project in collaboration with French, Swedish and Portuguese colleagues.
Other research activities
During the period covered by the fellowship, I carried on conducting research on a long-term project with which I have been involved for several years that investigates the adaptive basis of cooperative breeding in the sociable weaver Philetairus socius, an African passerine. During the duration of this Marie Curie fellowship I worked on two manuscripts, on of each is now published.
In addition, I continued work initiated previously on island parasites in the Gulf of Guinea. This project aims to determine whether insular bird species in these islands experience lower parasite pressures than their mainland counterparts and was done in collaboration with R. Fleischer and J. Beadell (Smithsonian Institute, Washington, USA). During this period we published one paper on the topic.