An international team of researchers has found that most of Madagascar’s unique present-day fauna may originally have arrived across long distances by air or sea.
Day gecko Phelsuma laticauda. Day geckos of the genus Phelsuma colonized most of the islands in the Indian Ocean and are today very common on Madagascar (Miguel Vences)
A study, published in the Proceedings of the National Academy of Sciences, suggests that the ancestors of the living Malagasy animals arrived on Madagascar after the island was fully isolated from other continents during the last 65 million years.
To reach the island vertebrates would have rafted, swum, or flown to the island, with the study suggesting that animals relying on swimming and rafting were most successful when winds and ocean currents worked in their favor and that, after the ocean currents reversed, the number of arrivals decreased markedly.
“The ancestors of most of the striking animals attracting today’s tourists to Madagascar arrived on the island around 60-70 million years before present. They all rafted over the ocean, mainly out of Africa,” said Prof. Miguel Vences of the University of Braunschweig, a co-author of the paper.
“We believe that flightless animals arrived virtually exclusively from Africa during the early part of the Cenozoic era by rafting and, after the shift in ocean currents, flying species became the dominant immigrants,” added Dr. Karen Samonds, a co-author of the paper and a researcher at the University of Queensland.
The study is the first to directly test the hypotheses of rafting and future studies are planned to scour the fossil record for “ghost lineages”: animals that came to Madagascar but then went extinct and were replaced by later arrivals.
“The findings of this study help us understand how islands accumulate biodiversity over time and can be used in modeling the time frame required to readjust following climate change or natural disasters,” Dr. Samonds explained. “Rafting as a general phenomenon applies to any landmass isolated by oceanic waters and the same kinds of modeling could be used to investigate other islands.”
To determine how and when Madagascar’s vertebrates arrived, the team combined biogeographic, geophysical, and oceanographic information, to analyze how arrival rates changed over time and relative to area of origin, prevailing ocean currents, and the island’s distance from other land masses.
“Some types of arrivals were not across the ocean (such as marsupials which arose while Australia was still part of Gondwana), but other arrivals to places like New Zealand and Fiji could be investigated by modeling ocean currents and winds in the same way,” Dr. Samonds said. “These findings are a step toward explaining the uniqueness of the fauna and the current species diversity of the world’s fourth largest island.”
