Abstract
Sweet potato dispersal from Americas to French Polynesia predates known human colonization periods, therefore being a long-standing dilemma. According to recent phylogenetic studies, the most likely hypothesis to explain this migration is the sea-drift long-distance dispersal, but no research indicating the response of I. batatas seeds to seawater conditions have been performed so far. The aim of this study was to understand seawater resistance in I. batatas, an essential feature for the sea-drift natural dispersal hypothesis, thus shedding light on the historical biogeography of this species, which also has implications on human civilization history, as the archaeological presence of sweet potato in both continents has been used as an evidence of pre-Columbian contacts between ancient civilizations. The experiment consisted of submitting sweet potato seeds to seawater treatments and observing the respective germination rates after different periods of immersion. Subsequently, one-way ANOVAs were conducted to test for significant differences between groups. All seeds from the seawater immersion treatments germinated, which confirms that I. batatas seeds are resistant to seawater salinity for a period of 120 days. Our results support the sea-drift natural dispersal hypothesis, thus shedding light on part of the logical conditions for one of the major hypotheses on the historical biogeography of this species, which also plays an important role in the discussions related to prehistorical human mobility in Polynesian islands.
Highlights
Sweet potato (Ipomoea batatas (L.) Lam.) is among the most important staple crops in the world, with an annual production of over a hundred million tons in 2016 (FAO 2016)
Research that brings new insights on sweet potato origin, domestication, and dispersal is interesting because it helps to solve a long-standing puzzle — namely, how sweet potato reached the Polynesian islands from America — but are valuable because they help understand how plants evolved and colonized different areas of the planet
Findings related to sweet potato biogeography may shed light on human civilization history and on hypotheses of pre-historic contacts between Polynesians and Americans following sea crossings
Summary
Sweet potato (Ipomoea batatas (L.) Lam.) is among the most important staple crops in the world, with an annual production of over a hundred million tons in 2016 (FAO 2016). Ancient Polynesians were eximious sailors, having discovered many Pacific islands since their arrival in the Solomon Islands about 3,100 years ago (Burley, Weisler & Zhao 2012) Such contacts would have been made through rafts that crossed the Pacific, and Heyerdahl (1973) performed the most famous experiment exploring this possibility. A recent study has found a common genetic ancestry between native Polynesians and Americans, but the timing of early human contacts is estimated to be around 3,000 years ago (Ioannidis et al 2020), which is much more recent than the archaeological findings of sweet potato in both continents. After examining cultivars from South America and Oceania, Rossel et al (2010) did not find significant genetic association among them; instead, gene flow was found between germplasm from Oceania and Mexico, and authors suggested natural dispersal as a possibility, in accordance with other investigations (Montenegro et al 2008, Williams et al 1990, Gichuki et al 2003)
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