Local Climate Heterogeneity Shapes Population Genetic Structure of Two Undifferentiated Insular Scutellaria Species

Abstract

Spatial climate heterogeneity may not only affect adaptive gene frequencies but could also indirectly shape the genetic structure of neutral loci by impacting demographic dynamics. In this study, the effect of local climate on population genetic variation was tested in two phylogenetically close Scutellaria species in Taiwan. Scutellaria taipeiensis, which was originally assumed to be an endemic species of Taiwan Island, is shown to be part of the widespread species S. barbata based on the overlapping ranges of genetic variation and climatic niches as well as their morphological similarity. Rejection of the scenario of “early divergence with secondary contact” and the support for multiple origins of populations of S. taipeiensis from S. barbata provide strong evolutionary evidence for a taxonomic revision of the species combination. Further tests of a climatic effect on genetic variation were conducted. Regression analyses show nonlinear correlations among any pair of geographic, climatic, and genetic distances. However, significantly, the bioclimatic variables that represent the precipitation from late summer to early autumn explain roughly 13% of the genetic variation of our sampled populations. These results indicate that spatial differences of precipitation in the typhoon season may influence the regeneration rate and colonization rate of local populations. The periodic typhoon episodes explain the significant but nonlinear influence of climatic variables on population genetic differentiation. Although, the climatic difference does not lead to species divergence, the local climate variability indeed impacts the spatial genetic distribution at the population level.

Genetic Divergence and Relationship Among Opisthopappus Species Identified by Development of EST-SSR Markers

“…The presence or absence of each SSR fragment was coded as "1" and "0, " respectively, and only clear and reproducible bands were considered. For the neutrality test of microsatellite alleles, we used the Bayesian-based outlier analysis of the multinomial-Dirichlet model (BayeScan analysis) to assess the F ST distribution among all alleles by BAYESCAN v 2.1 (Beaumont and Nichols, 1996;Hsiung et al, 2017).…”

Taxonomic notes on Scutellaria taipeiensis (Lamiaceae) from morphological and molecular data

“…Thus, our observation covered all populations in Taiwan. Observation of the nutlet sculpture of Hsiung et al (2017) was applied here as a reference. The identification of S. barbata, S. taipeiensis and other Taiwanese species was according to the protologues of Huang et al (2003) and other related literature (Hsieh and Huang 1995;Huang et al 1998).…”

“…The species, selected for analysis, were from Chiang et al (2012) and Holmskioldia sanguinea was applied as outgroup, since it was closely related to Scutellaria (Bendiksby et al 2011). Two nuclear (CAD, CHS) and three chloroplast DNA fragments (matK, ndhF-rpl32 and rpl32-trnL) were used by Chiang et al (2012), amongst them, ndhF-rpl32 and rpl32-trnL being also applied in the study of Hsiung et al (2017). Two chloroplast regions (ndhF-rpl32 and rpl32-trnL) were applied in the phylogenetic analysis of this study.…”

“…Two chloroplast regions (ndhF-rpl32 and rpl32-trnL) were applied in the phylogenetic analysis of this study. In addition to the sequences from Chiang et al (2012) and Hsiung et al (2017), Table 1. Sequences and accession number of sequences applied in this study.…”

“…Two new species, S. taipeiensis T. C. Huang, A. Hsiao & M. J. Wu and S. hsiehii T. H. Hsieh, were described subsequently (Huang et al 2003;Hsieh 2013). A genetic study of S. barbata D. Don and S. taipeiensis was conducted by Hsiung et al (2017) and the data showed no remarkable divergence between these two species. These results attracted our attention to verify their findings.…”