Simultaneous evaluation of the effects of geographic, environmental and temporal isolation in ecotypic populations ofSolidago virgaurea

Abstract

Early stages of ecological speciation can create populations with an ecology and reproduction timing distinct from those of related populations. Landscape genetic models incorporating environmental heterogeneity and population-specific reproductive traits enable the processes of population genetic differentiation to be inferred. We investigated genome-wide genetic variation in ecotypic populations of Solidago virgaurea sensu lato, a herbaceous plant inhabiting a wide range of habitats (woodlands, serpentine barrens and alpine grasslands) and displaying remarkable variation in flowering time. Simultaneous evaluation of environmental factors revealed an overwhelming effect of soil type differences on neutral genetic differentiation, compared with elevational differences. This result probably reflects the abrupt environmental changes generated by geological boundaries, whereas mountain slopes exhibit clinal changes, facilitating gene exchange between neighbouring populations. Temporal isolation was positively associated with genetic differentiation, with some early-flowering serpentine populations having allele frequencies distinct from adjacent nonserpentine populations. Overall, this study highlights the importance of ecological processes and of evolution of flowering time to promote genetic differentiation of S. virgaurea populations in a complex landscape.

Phylogeographic testing of alternative histories of single‐origin versus parallel evolution of early flowering serpentine populations of Picris hieracioides L. (Asteraceae) in Japan

“…The population genetic data analysis was performed following Sakaguchi et al (2017). Principal component analysis (PCA) was applied to the whole dataset (113 individuals from 50 populations in East Asia) as a nonmodel based ordination method to extract synthetic variables, on which genetic variation between individuals is maximized.…”

“…Each isolated serpentine patch has a distinct combination of serpentine endemic plant species with some serpentine endemic species absent from particular patches, likely reflecting factors of dispersal limitation, past extinction events, and environmental filtering (Kitamura 1957;Mizuno et al 2009). A recent phylogeographic analysis of Solidago virgaurea L. (goldenrod; Asteraceae) revealed that the northern and southern serpentine populations showed little genetic differentiation, although they exhibited clear morphological and flowering time differentiation, while central areas were characterized by highly divergent serpentine populations (Sakaguchi et al 2017). The finding suggests that the serpentine ecotypes originated multiple times in geographically distant areas for this species.…”

“…To date, genetic evidence for repeated origin (parallel evolution) of serpentine ecotypes have been obtained in Asteraceae (Rajakaruna et al 2003), Caryophyllaceae (Berglund et al 2004), andBrassicaceae (Turner et al 2010) from North America and Europe, as well as others. Examples are also known from the Japanese Archipelago, demonstrating that isolated serpentine populations are derived independently from geographically close non-serpentine populations (Kawase et al 2007;Yokoo et al 2009;Sakaguchi et al 2017).…”

Maintenance of soil ecotypes ofSolidago virgaureain close parapatry via divergent flowering time and selection against immigrants

“…Morphological differentiation between ecotypes (serpentine plants having smaller leaves than nonserpentine types [Figure d]) and differences in flowering time are reported (Kadota, ; Murata, ). The serpentine ecotypes do not show any qualitative differentiation in flowers and other morphological traits, and are shown to be closely related to the surrounding nonserpentine Solidago populations (Sakaguchi, Horie, Ishikawa, et al., ), making them suitable to study the adaptation and genetic interactions of populations in the process of ecotypic differentiation and possibly early stages of speciation (Sakaguchi, Kimura, et al., ).…”

Natural revegetation potential of Japanese wild thyme (Thymus quinquecostatus Celak.) on serpentine quarries

“…Aoba because their seed pods dropped easily from the receptacles, and their germination rates were very low (1 and 11%, respectively in October 2016). Like Solidago virgaurea sensu lato (Sakaguchi et al 2017), a herbaceous plant inhabiting a wide range of habitats (woodlands, serpentine barrens, and alpine grasslands), remarkable variation in flowering time may promote genetic differentiation of Japanese thyme, but we speculate that Sugashima thyme keeps these traits because only Sugashima has no snow in winter (other thymes overwinter under snow over 3 months in their place of origin). Sugashima thyme has a long period for blooming and seeding, and these may be advantageous to its spread compared to vegetative propagation only.…”