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201224Mar09:19

Ances­tors of Madagascar’s ver­te­brates arrived by air or sea

Infor­ma­tion
pub­lished 24 March 2012 | mod­i­fied 24 March 2012
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A recent study has found that most of present-​day fauna of Mada­gas­car, the world’s fourth largest island, may orig­i­nally have arrived across long dis­tances by air or sea. The island of Mada­gas­car is home to many unique ver­te­brate species, but how, when, and from where Madagascar’s ver­te­brates arrived on the island is a poorly under­stood mystery.

A group of inter­na­tional researchers now reveal that it is most likely that those vertebrate-​arrivals swum, rafted or flew the long dis­tance across the ocean. The researchers analysed data (arrival date, source, and ances­tor type) on ver­te­brate arrival pat­terns of cur­rently exist­ing tax­o­nomic groups.

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
The sci­en­tists con­clude that most species arrived after the island was fully iso­lated from other con­ti­nents dur­ing the last 65 mil­lion years (the Ceno­zoic Era). And not sur­pris­ingly, the prob­a­bil­ity of suc­cess­ful transoceanic arrival is neg­a­tively cor­re­lated with dis­tance trav­eled, but also influ­enced by ocean cur­rents and ances­tor type (aquatic, ter­res­trial, volant).

The study sug­gests that species that relied on swim­ming (like croc­o­diles) or raft­ing, using land masses as rafts, and exclu­sively com­ing from Africa’s main­land, were most suc­cess­ful when winds and ocean cur­rents worked in their favour. As soon as the ocean cur­rents shifted, fly­ing species such as bats became the main immi­grants. “These find­ings are a step toward explain­ing the unique­ness of the fauna and the cur­rent species diver­sity of the world’s fourth largest island,” accord­ing Karen Samonds, one of the authors.

(Sources: PNAS, 19.03.2012; Sci­enceAl­ert, 21.03.2012)

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