Oceanic dispersal

For using rafts as a sport or pleasure event, see Rafting.

Oceanic dispersal is a type of biological dispersal that occurs when organisms transfer from one land mass to another by way of a sea crossing on large clumps of floating vegetation. Such matted clumps of vegetation are often seen floating down major rivers in the tropics and washing out to sea, occasionally with animals trapped on them.^[1] This is sometimes referred to as a "rafting event."

Rafting has played an important role in the colonization of isolated land masses, such as Madagascar, which has been isolated for ~120 million years (Ma), and South America, which was isolated for much of the Cenozoic. Both land masses, for example, appear to have received their primates by this mechanism. According to genetic evidence, the common ancestor of the lemurs of Madagascar appears to have crossed the Mozambique Channel by rafting between 50 and 60 Ma ago.^[2][3][4] Likewise, the New World monkeys are thought to have originated in Africa and rafted to South America by the Oligocene, when the continents were much closer than they are today.^[3] Madagascar also appears to have received its tenrecs (25-42 Ma ago), nesomyid rodents (20-24 Ma ago) and euplerid carnivorans (19-26 Ma ago) by this route,^[4] and South America its caviomorph rodents (over 30 Ma ago).^[5][6]

Among reptiles, several iguanid species in the South Pacific have been hypothesized to be descended from iguanas that rafted over 8000 km from Central or South America^[7] (an alternative theory involves dispersal of a putative now-extinct iguana lineage from Australia or Asia^[8]). Similarly, skinks of the related genera Mabuya and Trachylepis apparently both floated across the Atlantic from Africa to South America and Fernando de Noronha, respectively, during the last 9 Ma.^[9] Skinks from the same group have also rafted from Africa to the Cape Verde islands, Madagascar, the Seychelles, the Comoros and Socotra.^[9] (Among lizards, skinks and geckoes seem especially capable of surviving long transoceanic journeys.^[9])

Colonization of groups of islands can occur by an iterative rafting process sometimes called island hopping. Such a process appears to have played a role, for example, in the colonization of the Caribbean by several groups of mammals of South American origin.^[10]

However, oceanic dispersal of terrestrial species may not always take the form of rafting; in some cases, swimming or simply floating may suffice. Tortoises of the genus Chelonoidis arrived in South America from Africa in the Oligocene;^[11] they were probably aided by their ability to float with their heads up, and to survive up to six months without food or fresh water.^[11]

See also

• Allopatric speciation
• Biological dispersal

References

1. ^ Mittermeier, R.A.; et al. (2006). Lemurs of Madagascar (2nd ed.). Conservation International. pp. 24–26. ISBN 1-881173-88-7. 
2. ^ Roos, Christian; Schmitz, Jürgen, & Zischler, Hans (July 2004). "Primate jumping genes elucidate strepsirrhine phylogeny" (PDF). PNAS 101 (29): 10650–10654. Bibcode 2004PNAS..10110650R. doi:10.1073/pnas.0403852101. PMC 489989. PMID 15249661. http://www.pnas.org/content/101/29/10650.full.pdf. 
3. ^ ^{a b} Sellers, Bill (2000-10-20). "Primate Evolution" (PDF). University of Edinburgh. pp. 13–17. http://homepage.mac.com/wis/Personal/lectures/human-origins/PrimateEvolution.pdf. Retrieved 2008-10-23. 
4. ^ ^{a b} Ali, J. R.; Huber, M. (2010-01-20). "Mammalian biodiversity on Madagascar controlled by ocean currents". Nature (Nature Publishing Group) 463 (4 Feb. 2010): 653–656. Bibcode 2010Natur.463..653A. doi:10.1038/nature08706. PMID 20090678. http://www.nature.com/nature/journal/vaop/ncurrent/full/nature08706.html. Retrieved 2010-01-20. 
5. ^ Flynn, J. J.; Wyss, A. R. (1998). "Recent advances in South American mammalian paleontology". Trends in Ecology and Evolution 13 (11): 449–454. doi:10.1016/S0169-5347(98)01457-8. PMID 21238387. 
6. ^ Flynn, John J.; Wyss, André R.; Charrier, Reynaldo (2007). "South America's Missing Mammals". Scientific American (May): 68–75. http://www.scientificamerican.com/article.cfm?id=south-americas-missing-mammals. 
7. ^ Gibbons, J. R. H. (Jul. 31, 1981). "The Biogeography of Brachylophus (Iguanidae) including the Description of a New Species, B. vitiensis, from Fiji". Journal of Herpetology (Society for the Study of Amphibians and Reptiles) 15 (3): 255–273. doi:10.2307/1563429. JSTOR 1563429. 
8. ^ Noonan, B.P.; Sites, J. W., Jr. (2009-11-24). "Tracing the origins of iguanid lizards and boine snakes of the Pacific". The American Naturalist (University of Chicago Press) 175 (1): 61–72. doi:10.1086/648607. PMID 19929634. 
9. ^ ^{a b c} Carranza, S.; Arnold, N. E. (2003-08-05). "Investigating the origin of transoceanic distributions: mtDNA shows Mabuya lizards (Reptilia, Scincidae) crossed the Atlantic twice". Systematics and Biodiversity (Cambridge University Press) 1 (2): 275–282. doi:10.1017/S1477200003001099. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=168963. Retrieved 2008-04-04. 
10. ^ Hedges, S. Blair (2006-08-23). "Paleogrography of the Antilles and Origin of West Indian Terrestrial Vertebrates". Annals of the Missouri Botanical Garden (Missouri Botanical Garden) 93 (2): 231–244. doi:10.3417/0026-6493(2006)93[231:POTAAO]2.0.CO;2. http://www.bioone.org/doi/abs/10.3417/0026-6493%282006%2993%5B231:POTAAO%5D2.0.CO%3B2. Retrieved 2010-01-14. 
11. ^ ^{a b} Le, M.; Raxworthy, C. J., McCord, W. P., Mertz, L. (2006-05-05). "A molecular phylogeny of tortoises (Testudines: Testudinidae) based on mitochondrial and nuclear genes". Molecular Phylogenetics and Evolution 40 (2): 517–531. doi:10.1016/j.ympev.2006.03.003. PMID 16678445. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WNH-4JWFGYC-1&_user=4430&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000059594&_version=1&_urlVersion=0&_userid=4430&md5=17737ababb8f6b572a3a44a520001dc6. 

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