Much has been made of the economic impacts of recent biologicalinvasions, but what are the implications of invasions in deep time?Luiz Rocha leads geneticists who time travel through oceanenvironments. The results of their travels, published online inMolecular Ecology, tell us that during warm, interglacial periods,reef-associated fish (goby genus Gnatholepis), leapt around the horn ofAfrica into the Atlantic, where their range expanded as the worldwarmed.
"We found that global warming events correspond clearly with majorrange expansions of gobies from the Indian Ocean into the AtlanticOcean and subsequently into the Eastern Atlantic," summarizes Rocha. Achilly Antarctic current--the Benguela upwelling system-- surges upalong the western coast of Africa acting as a natural barrier, and hasprevented most warm water organisms from the Indian Ocean from makingit in to the Atlantic for the last 2 million years. But when the worldwarmed about 150,000 years ago, gobies slipped around the corner of thecontinent.
Researchers at the Smithsonian Tropical Research Institute,Scripps Institution of Oceanography, Hofstra University and theUniversity of Hawaii, sequenced goby DNA (774 pb of the mtDNA ofcytochrome b, to be exact) from the western, central and easternAtlantic Ocean. They also sequenced DNA from gobies in the same genusfrom South Africa, from the Cocos Keeling Islands in the eastern IndianOcean, and from the Cook Islands in the South Pacific. They calculatethe approximate amount of time that isolated groups of fish have beenseparate based on the differences in the DNA between groups.
What evidence do they have that makes them think that Atlanticgobies are invaders? "The Atlantic goldspot goby certainly is a primecandidate-it's the only species of the genus in the Atlantic and thereare eight species and subspecies in the Indo-Pacific. It's reallysimilar to a sister taxon in the Indian Ocean," Rocha continues. "Wenailed down the timeline of the invasion by sequencing--the last timethere was tropical ocean connecting these two areas was 2 million yearsago. We calculate that these fish invaded the Atlantic Ocean during awarm period about 150,000 years ago and arrived in the eastern Atlanticonly 30,000 years ago."
What future effects of climate change might we expect in themarine realm? "Genetic analysis told us that fish from the Indian Oceanbreached the Benguela barrier in the past, and this barrier seems toopen intermittently. It would be reasonable to expect that otherorganisms limited by cold water barriers will continue to expand theirranges during warm periods."
Ref. Rocha, L.A., Robertson, D.R., Rocha, C., Van Tassell, J.L., Craig,M.T., Bowen, B.W. 2005. Recent invasion of the tropical Atlantic by anIndo-Pacific coral reef fish. Molecular Ecology online.
The Smithsonian Tropical Research Institute (STRI), a unit ofthe Smithsonian Institution, with headquarters in Panama City, Panama,was established to further our understanding of tropical nature and itsimportance to human welfare, to train students to conduct research inthe tropics and to promote conservation by increasing public awarenessof the beauty and importance of tropical ecosystems.
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