Teasing apart native status of a globally distributed species.
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- Gildenhuys et al 2015 - From the Neotropics to the Namib: Evidence for rapid ecological divergence following extreme long-distance dispersal
When it comes to protecting ecosystems from human driven disturbances sometimes it is not clear which elements are anthropogenic . Management strategies for invasive species can have severe ramifications from unintended interactions of biological controls in nontarget native populations. In the case of Balloon vines, genus Cardiospermum which is widely distributed but whose pre-industrial native range is uncertain, an uninformed strategy targeting one 'invasive' species of balloon vine may spill over to damage other 'native' vine species. In a recently published study on the biogeography of Cardiospermum species scientists sought to shed light on the enigmatic distributions of balloon vines by looking at the genetic relations of specimens collected world wide.
The Americas have the greatest species diversity of balloon vine, suggesting the 18 or so known species have originated and spread from there.. Species C. halicacabum and C. grandiflorum, which are widely planted as ornamentals, are found in the Americas, Hawaii, South Africa, Australia, and across the South Pacific. C. corindum is found in both the Americas and in Africa. The species C. pechuellii is only found in southwestern Africa where it appears to be more desert adapted than its counterparts.
In South Africa, where C. grandiflorum is a top 5 environmental weed, and its control program focuses on the biological method of importing the pests that attack it in its native range in Argentina. Progress is hampered by the concern of spillover to the other balloon vine species in the southern African ecosystem. But are they native?
Three hypotheses offer solutions to the puzzle of balloon vine origins in Africa and there questionable native status (figure below).
1. Balloon vines may have been present in both Africa and South America before the continents broke apart (a), this is unlikely as past work on their molecular clocks calculate the split between the species happening after the split of the continents.
2. Powerful winds or prolonged a sea journey sometime in the past carried balloon vine seeds across the Atlantic.
3. The third possibility is through human facilitated transfer, which would render the species non-native.
By comparing DNA within the chloroplasts of samples around the world, we were able to determine that two species, C. grandiflorum and C. halicacabum re genetically similar to the American samples, which supports the invasive status of these plants, as their introduction has been made recently and is more than likely anthropogenic. However, C. corindum and C. pechuelli share genes on common and appear to have a common ancestor dating back to a time before human, supporting the second hypothesis of a transatlantic journey of C. corindum from America to Africa and a speciation event giving rise to C. pechuelli. These two species would be considered native, therefore caution should be placed in protecting them from harm caused by the control of the two non native balloon vine species. Teasing out the relatedness and origin of globally distributed species is an important step in moving toward a dynamic and calculated effort to combat some of the destructive elements of human globalization.