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Rick, C. M., & Bowman, R. I. (1961). Galápagos tomatoes and tortoises. Evolution, 15(4), 407–417. 
Added by: Admin (29 Jan 2012 12:39:07 UTC)
Resource type: Journal Article
BibTeX citation key: Rick1961
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Categories: General
Keywords: Chelonoidis, Chelonoidis nigra, Ernährung = nutrition, Schildkröten = turtles + tortoises, Testudinidae
Creators: Bowman, Rick
Collection: Evolution
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Abstract     
Testudinidae Geochelone nigra Seeds of tomato species native to the Galápagos Islands are subject to extreme seed dormancy of indefinite duration. The dormancy is alleviated by treating the seeds with a strong solution of sodium hypochlorite, which erodes the seed coat. In a search for natural dormancy-breaking devices, the following treatments proved ineffective: soaking in stagnant or well-aerated water, various temperatures applied to wet or dry seeds, application of acids, planting in native soil, and passage through the gut of immature chickens. Additionally, seeds collected from rat droppings found under plants in their native habitat did not germinate. On the other hand, digestion by the native giant tortoise results in marked improvement in speed and percentage of germination, the degree of response varying with the tomato biotype. Passage through the tortoise gut required from one to three weeks and probably longer. In all tests a minimum of one-quarter of the ingested seeds was recovered, and the seeds revealed no macroscopic effects of digestion. The dormancy mechanism most likely responsible is one of simple mechanical obstruction of emergence by the seed coat. These results suggest that the giant tortoise might be an important natural agent not only in breaking the dormancy but also in effectively dispersing the tomato seeds. Following tortoise digestion, seeds of the garden tomato, which are not prone to dormancy, germinated but at a lower percentage than that of untreated seeds. The digestive reaction that is most likely responsible for alleviating dormancy, the possible role of other animal agents on the Galápagos Islands, and evolutionary aspects of animal digestion as a promoter of germination and of dispersal of plant seeds are discussed.
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