"Beginning in the 1950s we thought that bottle gourds floated across the ocean from Africa," said Logan Kistler, post-doctoral researcher in anthropology, Penn State. "However, a 2005 genetic study of gourds suggested an Asian origin."
Domesticated bottle gourds are ubiquitous around the world in tropical and temperate areas because, while they are edible when young, the mature fruit make ideal lightweight, waterproof, liquid-carrying vessels. They were popular in areas either before development of ceramics or where ceramics never developed.
The 2005 study looked only at targeted sequence markers that turned out not to be informative on the population level, said Kistler. Now we can do sequencing of the large single copy area of the plastid genome, which is about 86,000 base pairs of DNA, he added.
Unlike animals, which have two types of DNA -- nuclear and mitochondrial -- plant cells have three types of DNA -- nuclear, mitochondrial and plastid. Animal mitochondrial DNA is often used in genetic studies because it is completely inherited from the mother and changes very slowly, but in plants, mitochondrial DNA is prone to structural rearrangements, while often carrying a slow mutation rate. The DNA found in plastids such as the organelles that perform photosynthesis and create starch or pigments, is a better choice for plants because it does not recombine, but it mutates fast enough for population-level studies.
The researchers, who report their results in a recent issue of the Proceedings of the National Academy of Sciences, looked at 36 modern samples of bottle gourd and 9 ancient samples. They found that all the ancient bottle gourds from the Americas that were tested fell within the normal variation of the African bottle gourds and not the Asian bottle gourds.
"The best explanation for this is that they came directly from Africa," said Kistler. "However, we wanted to test the possibility that gourds did float from Africa to form New World populations."
Previous studies found that gourds do float in the oceans and that after long periods of time in the ocean they still have viable seeds. The researchers developed an ocean-current drift model that showed that wild African gourds could have simply floated across the Atlantic during the Late Pleistocene. They suggest that large mammals like the mammoth helped naturalized populations establish in the neotropics, because these large mammals were known to eat various members of the family that includes gourds. The seeds are found in ancient deposits of large mammal dung.
Bottle gourds in Africa exist today mostly in the domesticated form, with only small populations of the wild variety in Kenya and Zimbabwe. In the ocean drift model, the researchers looked at realistic, unrealistically conservative and optimistic scenarios. They divided the western coast of Africa by latitude and simulated 12 years of gourd release where one gourd per month entered the ocean in each latitude division. The shortest amount of time it took for a gourd to arrive was 100 days, with an average arrival time of about nine months.
According to the researchers, it is feasible that gourds did float across the Atlantic Ocean frequently. This is especially true of gourds growing near rivers that flow into the ocean.
"It wasn't one gourd that came over and gave rise to all New World gourds," said Kistler. "Populations show up in Florida and Mexico around 10,000 years ago and in Central America a little later."
Also working on this project were Álvaro Montenegro, assistant professor or geography, Ohio State University; Bruce D. Smith, curator of North American archaeology, Smithsonian Institution; John A. Gifford, associate professor of marine affairs and policy; Richard E. Green, assistant professor of biomolecular engineering, University of California Santa Cruz; and Lee A. Newsome, associate professor of archaeological anthropology, Penn State.
The National Science Foundation partially supported this work.
A'ndrea Elyse Messer | EurekAlert!
Tropical deforestation releases large amounts of soil carbon
28.07.2015 | Georg-August-Universität Göttingen
Drivers of temporal changes in temperate forest plant diversity
27.07.2015 | Friedrich-Schiller-Universität Jena
Researchers have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second and could form the basis of optical computing.
Joint BioEnergy Institute study identifies bacterial protein that is key to protecting rice against bacterial blight
A bacterial signal that when recognized by rice plants enables the plants to resist a devastating blight disease has been identified by a multi-national team...
Researchers in the Cockrell School of Engineering at The University of Texas at Austin are one step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat and, conversely, to block light while allowing heat transmission, as described in two new research papers.
By allowing indoor occupants to more precisely control the energy and sunlight passing through a window, the new materials could significantly reduce costs for...
Argonne scientists used Mira to identify and improve a new mechanism for eliminating friction, which fed into the development of a hybrid material that exhibited superlubricity at the macroscale for the first time. Argonne Leadership Computing Facility (ALCF) researchers helped enable the groundbreaking simulations by overcoming a performance bottleneck that doubled the speed of the team's code.
While reviewing the simulation results of a promising new lubricant material, Argonne researcher Sanket Deshmukh stumbled upon a phenomenon that had never been...
A NASA camera on the Deep Space Climate Observatory (DSCOVR) satellite has returned its first view of the entire sunlit side of Earth from one million miles away.
The color images of Earth from NASA's Earth Polychromatic Imaging Camera (EPIC) are generated by combining three separate images to create a...
23.07.2015 | Event News
10.07.2015 | Event News
25.06.2015 | Event News
28.07.2015 | Life Sciences
28.07.2015 | Materials Sciences
28.07.2015 | Ecology, The Environment and Conservation