Professor Mathieu Rouget.

UKZN’s Chair of Land Use Planning and Management in the School of Agricultural, Earth and Environmental Sciences (SAEES), Professor Mathieu Rouget, contributed to groundbreaking research concerning the dispersal of Acacia koa between Hawaii and Réunion Island in the Indian Ocean which appeared as a news story in Nature recently (Nature 510, 320–321, doi:10.1038/510320a).

The research was originally published in the New Phytologist journal (Le Roux et al., 2014, DOI: 10.1111/nph.12900).

The Nature article tells the story of a tree species which migrated 18 000km from Hawaii to Reunion Island around 1.4 million years ago. The study, which was led by Professor Johannes Le Roux, a Molecular Ecologist at Stellenbosch University, proposes that the seed of the Acacia koa of Hawaii was brought to Réunion by a sea bird. The study confirms, through genetic analysis and environmental niche modelling, that the A. koa is in fact the same species as the Acacia heterophylla endemic to Réunion. This is most likely the farthest dispersal of a species that has been recorded.

Rouget, in his capacity as Chair of Land Use Planning and Management, assisted with the mapping of the dispersal in the study and visited Réunion in the process of completing this research. Rouget’s research interests include alien plant invasions and biodiversity patterns and he uses Geographic Information Systems (GIS) in addressing conservation issues in Africa.

The study is remarkable for finally confirming the relation of the two trees originating from two small islands so far apart, whose similarities have long been recognised. The study established, via genetic sequencing, that all A. heterophylla are in fact more closely related to one kind of Hawaiian koa than some other kinds of koa are to each other.

The study, titled “Relatedness Defies Biogeography: the Tale of Two Island Endemics (Acacia heterophylla and A. koa)” was originally published in the New Phytologist journal, which focuses on plant science. The study was a collaboration between Rouget and le Roux, as well as Professor Clifford Morden of the University of Hawaii at Manoa, Ms Megan Koordom of the Centre for Invasion Biology (CIB) at Stellenbosch University, Professor Dominique Strasberg of the University of Réunion and Professor David Richardson of CIB at Stellenbosch University.

These findings have caused a stir in biogeography, a field of study which examines why certain species are found in certain habitats. The study is one in a long line of surprising discoveries related to dispersal of plant and animal species over long distances, which were previously assumed to have taken place as a result of continental drifts, and certainly not from one small island to another across the globe.

These kinds of studies have raised questions about the randomness about such dispersals and the possibility of being able to predict patterns of seemingly chance dispersals at some point in the future, leaving many opportunities for collaborative groups like this one to expand scientific knowledge on biogeography.

The news article is available in Nature (https://www.nature.com/news/tree-hitched-a-ride-to-island-1.15419) and the original article in New Phytologist

(https://onlinelibrary.wiley.com/doi/10.1111/nph.12900/abstract;jsessionid=FA1A63FD44286CFC3817E83E9F9D4BDB.f02t04)