Evolution in island birds and the ‘insularity’ syndrome
Islands are important centres of endemism and key ‘laboratories’ for the study of ecology and evolution. However, some aspects of island ecology and evolution remain poorly understood. This programme studies patterns of adaptation and speciation on islands worldwide and conducts detailed studies using the Gulf of Guinea, Cape Verde and Tristan islands as study systems.
The Theory of Island Biogeography, which predicts how species richness on an island is a function of its size and isolation, remains one of the most elegant of ecological theories. Although the theory’s architects, MacArthur and Wilson, were aware of the importance of speciation after colonisation, they were unable to include this variable in the model. In a project led by Luis Valente, we addressed this lack. By comparing sequences from almost 600 island birds from 41 archipelagos with those of their mainland relatives, we were able to estimate colonisation times and speciation rates. Amazingly, the empirical shape of the relationships between colonisation, extinction and speciation with island area and isolation is best explained by the original island biogeography model. With these results to be published in early 2020, we have initiated a pilot project to investigate communities from continental islands (i.e. those that were formerly linked to the mainland), starting with a sampling expedition to Bioko in the Gulf of Guinea in February 2020.
The Iago Sparrow Passer iagoensis occurs on most islands of the Cape Verde archipelago, and Martim Melo initiated a study of its adaptation to aridity. Long considered part of the Great Sparrow P. motitensis superspecies, genetic evidence places it sister to the Dead Sea P. moabiticus and Golden P. luteus Sparrows. Neutral genetic data from sparrows across all islands, obtained by RAD-sequencing in Rauri Bowie’s lab, are being combined with full genome data from Mark Ravinet’s lab to understand the links between environment, phenotype and genotype.
Islands typically have impoverished communities, and our previous work confirmed that this extends to parasite diversity. Low parasite levels could lead to weaker immune systems, as suggested by the extinction of many Hawaiian birds after the accidental introduction of a malaria vector. This hypothesis is currently being studied through a collaboration between Claire Doutrelant, Rita Covas, Martim Melo, Claire Loiseau and Benoit Nabholz, which is investigating the genes underlying specific types of immune response. Parasite diversity might increase in human-altered environments, so another study is investigating whether land-use practices influence avian parasites on São Tomé. Entomologists are documenting changes in the community of parasite vectors, a critical but often overlooked piece of this puzzle.
Activities in 2019
- Fieldwork on Príncipe Island found that the newly-discovered species of scops owl is fairly common in low-lying native forests, but has a small total range of only c. 30 km2. Visits were made to the British, Dresden and Frankfurt museums to complete the new species’ description.
- A survey along a gradient of human disturbance on São Tomé was conducted sampling birds, their parasites and parasite vectors, to assess the impact of human activities on bird-parasite interactions.
- Iago Sparrows: RAD-sequencing of 339 sparrows, and full genome sequencing of 23 Iago, 10 House and 10 Spanish Sparrows.
- Full genome sequences constructed for several São Tomé endemic birds and their mainland counterparts will be used to investigate whether insularity influences the evolution of the immune system by studying toll-like receptors.
- PhD student Alois Robert (U. Montpellier) showed that impoverished bird and insect communities affect the way birds sing on islands. MSc student, Louis Bliard (U. Montpelier) showed that impoverished predator communities affect plumage colour of island birds.
- Genomic data from Tristan’s Nesospiza finches collated by Bengt Hansson (Lund U.) and Martin Stervander (U. Oregon) have provided novel insights into this very recent adaptive radiation.
- Aloïs Robert was awarded a PhD for his work on the influence of community structure on acoustic signals in island birds. His paper on vocal differences between island and mainland birds was published in Journal of Biogeography and a second paper is in review.
- Louis Bliard received an MSc for his research on the role of avian predators in influencing the evolution of bird colouration on islands.
- Bárbara Freitas received an MSc degree for her work on the genetics and ecology of the newly discovered Princípe Island Scops-owl.
- A worldwide empirical analysis on colonisation times and speciation rates of oceanic island birds confirmed that MacArthur’s and Wilson’s Theory of Island Biogeography is robust to the inclusion of evolution in the process of the assembly of island communities.
Impact of the project
This project is uncovering novel patterns of adaptation in island birds and investigating the mechanisms underlying these adaptations. The results make a significant contribution to our understanding of the ecology and evolution of island environments. Given the high number of species endemic to islands worldwide and the threats to these faunas, our work will help to understand and conserve island species
Forever Principe, National Geographic, CNRS (PEPS), University of Montpellier (PhD grant to Alois Robert), LIA Biodiversity, Portuguese Science and Technology Foundation.
Research team 2019
Dr Martim Melo (FIAO, UCT /CIBIO, U. Porto)
Dr Claire Doutrelant (CNRS / FIAO, UCT)
Dr Rita Covas (FIAO, UCT / CIBIO, U. Porto)
Dr Claire Loiseau (CIBIO, U. Porto)
Dr Mark Ravinet (U. Nottingham)
Dr Martin Stervander (U. Oregon)
Dr Luis Valente (Naturalis Biodiversity Center, Leiden)
Prof. Rauri Bowie (U. California Berkeley)
Prof. Bengt Hansson (Lund U.)
Prof. Peter Ryan (FIAO, UCT)
Students: Sandra Reis (PhD, CIBIO, U. Porto); Aloïs Robert (PhD, CNRS and U. Montpellier); Bárbara Freitas (MSc, CIBIO, U. Porto); Louis Bliard (MSc, CNRS and U. Montpellier).