Genetic evidence of the southward founder speciation of Cycas taitungensis from ancestral C. revoluta along the Ryukyu Archipelagos
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Cycas taitungensis and its sister species, C. revoluta (Cycas sect. Asiorientalis), are distributed peripatrically. Previous studies have revealed their phylogeographic pattern and, based on certain plastid DNA markers, have established that they diverged recently. However, the speciation process involving the genomic divergence has not been well clarified. In this study, based on their geographical distribution and estimates of their genetic diversity, two speciation models are proposed: (1) the founder and (2) the bottleneck speciation mode. Using approximate Bayesian computation (ABC) in combination with their estimated genetic diversity and population structure, we infer that the ancestral C. taitungensis populations diverged and southward colonized southeastern Taiwan from ancestral C. revoluta since the middle Pleistocene. These founders preserved ancestral polymorphism, resulting in small differences in genetic diversity and effective population size (Ne), despite a large difference in census population size (Nc) between two species. Based on this case of island cycad species offshore of continental Asia, this study provides new insight into how the speciation process influences the genetic diversity pattern of species with small Nc and Ne.
KeywordsAFLP Asiorientalis Founder event Census population size Continental islands Effective population size
We would like to thank Chung-Wei You for his helpful sampling of C. revoluta among the Ryukyu Islands. We thank the National Center for Genome Medicine of the National Core Facility Program for Biotechnology, Ministry of Science and Technology, Taiwan, for technical and bioinformatics support. We acknowledge Chih-Chieh Yu and Hsiao-Lei Liu for the suggestion of contents. We also thank Dr. Hubert Turner for English editing of the manuscript. This research was financially supported by the Ministry of Science and Technology of Taiwan (Grant Number: MOST 105–2628-B-003–001-MY3 and MOST 105–2628-B-003–002-MY3) and was also subsidized by National Taiwan Normal University (NTNU), Taiwan.
JTC and PCL conceived the project and collected field samples. JTC conducted genetic experiments, performed statistical analyses, interpreted the data, and wrote the manuscript. BHH assisted in the genetic diversity and evolutionary analyses. PCL critically reviewed the draft. All authors read and approved the final manuscript.
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Conflicts of interest
The authors declare no conflict of interest.
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