J Syst Evol

• Research Articles •    

Species delimitation of North American Nyssa species

Yan-Ting Yang1†, Xu-Chen Yang1†, Ming-Cheng Wang1, Lin-Ling Zhong1, Rui Ma1, Tao Ma1, Jian-Quan Liu1,2, Charles C. Davis3*, and Zhen-Xiang Xi1*   

  1. 1Key Laboratory of Bio-Resource and Eco-Environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610065, China

    2State Key Laboratory of Grassland Agro-Ecosystems, College of Life Sciences, Lanzhou University, Lanzhou 730000, China

    3Department of Organismic and Evolutionary Biology, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA 02138, USA

  • Received:2020-08-18 Accepted:2020-12-26

Abstract: The development of next-generation sequencing technologies allows researchers to address complex problems in species delimitation, particularly for non-model organisms. The taxonomic status of North American Nyssa species has long been debated and remains controversial. To elucidate the genetic structure and phylogenetic relationships of the five currently recognized North American Nyssa species, we conducted whole-genome sequencing of representative individuals, and identified genome-wide single nucleotide polymorphisms (SNPs) by utilizing the recently released chromosome-level assembly of Nyssa sinensis genome. Population genetic and phylogenetic analyses consistently inferred four well supported genetic clusters from our sampled individuals, i.e., N. aquatica, N. ogeche, N. sylvatica, and N. biflora-N. ursina. Although the identification of N. biflora and N. ursina is primarily based on the morphological characteristics of leaves and drupes, the present evidence, including our principal components analysis of leaf morphological traits, strongly supports the taxonomic designation of N. biflora and N. ursina as a single species. In addition, these four genetic clusters were grouped into two major clades, i.e., clade 1 (N. aquatica and N. ogeche) and clade 2 (N. sylvatica and N. biflora-N. ursina). Despite the fact that no evidence of widespread gene flow was found between these two major clades, our analyses revealed the possibility of introgression from N. sylvatica into N. biflora, albeit at a relatively low frequency. This study demonstrates the use of whole-genome sequences as a promising avenue for delimiting species boundaries, and further advocates for an integrative approach in the assessment of species delimitation.

Key words: Nyssa, North America, species delimitation, whole-genome sequencing, population genomics