Long-distance dispersal of the coconut palm by migration within the coral atoll ecosystem
Background
The location of the original home of the coconut palm, Cocos nucifera, and the extent of its natural dispersal are not known. Proponents of a South American origin must explain why it is not indigenous there and why it shows greatest diversity in southern Asia. Conversely, proponents of an Asian origin must explain why there are no Asian Cocoseae and why the closest botanical relative to Cocos is in South America. Both hypotheses share the common problems of how, when, where and in what directions long-distance dispersal occurred.
Hypothesis
These difficulties are resolved by accepting that C. nucifera originated and dispersed by populating emerging islands of the coral atoll ecosystem, where establishment conditions impose high selection pressures for survival. When lifted by wave action onto virtually sterile, soilless coralline rocks just above sea level and exposed to the full impact of the sun, seednuts must germinate, root and establish vigorous populations. The cavity within the nut augments the buoyancy provided by the thick husk, which in turn protects the embryo and, by delaying germination, simultaneously extends viability while floating and provides a moisture-retentive rooting medium for the young seedling. These adaptations allow coconuts to disperse widely through the coral atoll ecosystem.
Conclusions
The monthly production of fruit and the long floating duration ensure that viable seednuts are always available in the lagoon to replace those destroyed by hurricanes and tsunamis, or to populate newly emerged coral atolls elsewhere. Long-distance dispersal is secondary, because it was the spontaneous, independent migration of coral polyps on a prolonged geological time scale that generated new coral atolls in new areas where the coconuts would be amongst the earliest inhabitants. The coconut palm became an intermittent, itinerant, pioneer endemic there, and also on suitable beaches on volcanic or large islands and continental coastlines.
Abstract
Background
The location of the original home of the coconut palm, Cocos nucifera, and the extent of its natural dispersal are not known. Proponents of a South American origin must explain why it is not indigenous there and why it shows greatest diversity in southern Asia. Conversely, proponents of an Asian origin must explain why there are no Asian Cocoseae and why the closest botanical relative to Cocos is in South America. Both hypotheses share the common problems of how, when, where and in what directions long-distance dispersal occurred.
Hypothesis
These difficulties are resolved by accepting that C. nucifera originated and dispersed by populating emerging islands of the coral atoll ecosystem, where establishment conditions impose high selection pressures for survival. When lifted by wave action onto virtually sterile, soilless coralline rocks just above sea level and exposed to the full impact of the sun, seednuts must germinate, root and establish vigorous populations. The cavity within the nut augments the buoyancy provided by the thick husk, which in turn protects the embryo and, by delaying germination, simultaneously extends viability while floating and provides a moisture-retentive rooting medium for the young seedling. These adaptations allow coconuts to disperse widely through the coral atoll ecosystem.
Conclusions
The monthly production of fruit and the long floating duration ensure that viable seednuts are always available in the lagoon to replace those destroyed by hurricanes and tsunamis, or to populate newly emerged coral atolls elsewhere. Long-distance dispersal is secondary, because it was the spontaneous, independent migration of coral polyps on a prolonged geological time scale that generated new coral atolls in new areas where the coconuts would be amongst the earliest inhabitants. The coconut palm became an intermittent, itinerant, pioneer endemic there, and also on suitable beaches on volcanic or large islands and continental coastlines.
ACKNOWLEDGEMENTS
We are grateful to Vimla Patil and Ron Blakey for supplying the images for Figs 1 and 2, respectively. And thanks, in advance, to the person who makes a good English language version of Chiovenda's original document.