Abstract
Discerning species boundaries among closely related taxa is fundamental to studying evolution and biodiversity. However, species boundaries can be difficult to access in plants because ongoing divergence and speciation may leave an evolutionary footprint similar to introgression, which occurs frequently among species and genera. In this study, we sought to determine species boundaries between two closely related alpine shrubs, Rosa sericea and Rosa omeiensis, using population genetics, environmental data and ecological niche modeling, and morphological traits. We analyzed populations of R. sericea and R. omeiensis using genetic markers comprising a fragment of the single-copy nuclear gene, LEAFY, micro-satellites (EST-SSR), and plastid DNA sequences. The DNA sequence data suggested clusters of populations consistent with geography but not with previously proposed species boundaries based on morphology. Nevertheless, we found that the ecological niches of the previously proposed species only partially overlap. Thus, we suspect that these species are in the process of parapatric speciation; that is, differentiating along an ecological gradient, so that they exhibit differing morphology. Morphology has previously been the basis of recognizing the species R. sericea and R. omeiensis, which are the most widely distributed species within a broader R. sericea complex that includes several other narrow endemics. Here, we recognize R. sericea and R. omeiensis as independent species based on morphological and ecological data under the unified species concept, which emphasizes that these data types are of equal value to DNA for determining species boundaries and refining taxonomic treatments. While the DNA data did not delimit species within the R. sericea complex, we expect to develop and utilize new, robust DNA tools for understanding speciation within this group in future studies.
Highlights
Species comprise a basic unit of biology and are fundamental to elucidating first order patterns in the organization of global, regional and local biodiversity, such as the latitudinal gradient of species richness (von Humboldt, 1807; Willig et al, 2003; Mannion et al, 2014), Asian species bias among eastern Asianeastern North American disjunct genera (Wen, 1999, 2001; Qian and Ricklefs, 2000), and the species-area relationship (Arrhenius, 1921)
Despite the centrality of species to understanding biology, biodiversity science, and conservation, delimiting species from one another remains a controversial exercise for biologists, so that dozens of species concept have been raised (De Queiroz, 2005, 2007; Hey, 2006; Freudenstein et al, 2017)
Many species concepts are narrow; focusing on one or a few aspects of reproductive isolation, such as genetic or morphological differences (De Queiroz, 2007; Aldhebiani, 2018). These narrow concepts are insufficient, because evolution is ongoing such that divergence may be incomplete in the present [e.g., Orinus Hitchc. (Liu et al, 2018), see (Funk and Omland, 2003; Arnold, 2016)] and may affect genetics, morphology, ecology, and other aspects of plant biology at different rates
Summary
Species comprise a basic unit of biology and are fundamental to elucidating first order patterns in the organization of global, regional and local biodiversity, such as the latitudinal gradient of species richness (von Humboldt, 1807; Willig et al, 2003; Mannion et al, 2014), Asian species bias among eastern Asianeastern North American disjunct genera (Wen, 1999, 2001; Qian and Ricklefs, 2000), and the species-area relationship (Arrhenius, 1921). Many species concepts are narrow; focusing on one or a few aspects of reproductive isolation, such as genetic or morphological differences (De Queiroz, 2007; Aldhebiani, 2018). These narrow concepts are insufficient, because evolution is ongoing such that divergence may be incomplete in the present [e.g., Orinus Hitchc. (Liu et al, 2018), see (Funk and Omland, 2003; Arnold, 2016)] and may affect genetics, morphology, ecology, and other aspects of plant biology at different rates. Like the ‘integrative species concept’ (Liu, 2016), the unified species concept aims to strike a balance among rival concepts and provide a practical philosophy of species delimitation
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