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Abstract Background Climate change is expected to alter the factors that drive changes in adaptive variation. This is especially true for species with long life spans and limited dispersal capabilities. Rapid climate changes may disrupt the migration of beneficial genetic variations, making it challenging for them to keep up with changing environments. Understanding adaptive genetic variations in tree species is crucial for conservation and effective forest management. Our study used landscape genomic analyses and phenotypic traits from a thorough sampling across the entire range of Quercus longinux, an oak species native to Taiwan, to investigate the signals of adaptation within this species. Results Using ecological data, phenotypic traits, and 1,933 single-nucleotide polymorphisms (SNPs) from 205 individuals, we classified three genetic groups, which were also phenotypically and ecologically divergent. Thirty-five genes related to drought and freeze resistance displayed signatures of natural selection. The adaptive variation was driven by diverse environmental pressures such as low spring precipitation, low annual temperature, and soil grid sizes. Using linear-regression-based methods, we identified isolation by environment (IBE) as the optimal model for adaptive SNPs. Redundancy analysis (RDA) further revealed a substantial joint influence of demography, geology, and environments, suggesting a covariation between environmental gradients and colonization history. Lastly, we utilized adaptive signals to estimate the genetic offset for each individual under diverse climate change scenarios. The required genetic changes and migration distance are larger in severe climates. Our prediction also reveals potential threats to edge populations in northern and southeastern Taiwan due to escalating temperatures and precipitation reallocation. Conclusions We demonstrate the intricate influence of ecological heterogeneity on genetic and phenotypic adaptation of an oak species. The adaptation is also driven by some rarely studied environmental factors, including wind speed and soil features. Furthermore, the genetic offset analysis predicted that the edge populations of Q. longinux in lower elevations might face higher risks of local extinctions under climate change.

Aspidistra Ker Gawl. is one of the the most diverse and fastest-growing genera of angiosperm. Most Aspidistra species have been discovered in a limited area or a single site through morphological comparison. Because of the lack of population studies, morphological variation within species and the boundaries of some species remain unclear. In recent years, combining genetic and morphological markers has become a powerful approach for species delimitation. In this study, we performed population sampling and integrated morphometrics and microsatellite genetic diversity analyses to determine the species diversity of Aspidistra in Taiwan. We identified three species, namely Aspidistra attenuata Hayata; A. daibuensis Hayata var. daibuensis; A. mushaensis Hayata var. mushaensis; and reduced A. longiconnectiva C.T.Lu, K.C.Chuang & J.C.Wang to the variety level, and described a new variety, A. daibuensis Hayata var. longkiauensis. The description, diagnosis, distribution, and photographs of this new variety as well as a key to the known Taiwanese Aspidistra are provided.

Abstract A cryptic lineage is a genetically diverged but morphologically unrecognized variant of a known species. Clarifying cryptic lineage evolution is essential for quantifying species diversity. In sympatric cryptic lineage divergence compared with allopatric divergence, the forces of divergent selection and mating patterns override geographical isolation. Introgression, by supplying preadapted or neutral standing genetic variations, can promote sympatric cryptic lineage divergence via selection. However, most studies concentrated on extant species introgression, ignoring the genetic legacy of introgression from extinct or unsampled lineages (“ghost introgression”). Cycads are an ideal plant for studying the influence of ghost introgression because of their common interspecific gene flow and past high extinction rate. Here, we utilized reference‐based ddRADseq to clarify the role of ghost introgression in the evolution of a previously identified sympatric cryptic lineage in Cycas revoluta. After re‐evaluating the evolutionary independency of cryptic lineages, the group‐wise diverged single‐nucleotide polymorphisms among sympatric and allopatric lineages were compared and functionally annotated. Next, we employed an approximate Bayesian computation method for hypothesis testing to clarify the cryptic lineage evolution and ghost introgression effect. SNPs with the genomic signatures of ghost introgression were further annotated. Our results reconfirmed the evolutionary independency of cryptic lineage among C. revoluta and demonstrated that ghost introgression to the noncryptic lineage facilitated their divergence. Gene function related to heat stress and disease resistance implied ecological adaptation of the main extant populations of C. revoluta.

Range expansion requires peripheral populations to shift adaptive optima to breach range boundaries. Opportunities for range expansion can be assessed by investigating the associations of core-periphery environmental and genetic differences. This study investigates differences in the core-periphery adaptation of Ammopiptanthus mongolicus, a broad-leaved evergreen shrub species in a relatively homogeneous temperate Asian desert environment, to explore the environmental factors that limit the expansion of desert plants. Temperate deserts are characterized by severe drought, a large diurnal temperature range, and seasonality. Long-standing adaptation to the harsh desert environment may confine the genetic diversity of A. mongolicus, despite its distribution over a wide range of longitude, latitude, and altitude. Since range edges defined by climate niches may have different genetic responses to environmental extremes, we compared genome-wide polymorphisms between nine environmental core populations and ten fragmented peripheral populations to determine the “adaptive peripheral” populations. At least four adaptive peripheral populations had similar genetic-environmental association patterns. High elevations, summer drought, and winter cold were the three main determinants of converging these four adaptive peripheral populations. Elevation mainly caused similar local climates among different geographic regions. Altitudinal adaptation resulting from integrated environmental-genetic responses was a breakthrough in breaching niche boundaries. These peripheral populations are also located in relatively humid and warmer environments. Relaxation of the drought and cold constraints facilitated the genetic divergence of these peripheral populations from the core population’s adaptive legacy. We conclude that pleiotropic selection synchronized adaptative divergence to cold and drought vs. warm and humid environments between the core and peripheral populations. Such parallel adaptation of peripheral populations relies on selection under a background of abundant new variants derived from the core population’s standing genetic variation, i.e., integration of genetic surfing and local adaptation.

The divergence process of incipient species is fascinating but elusive by incomplete lineage sorting or gene flow. Species delimitation is also challenging among those morphologically similar allopatric species, especially when lacking comprehensive data. Cycas sect. Asiorientales, comprised of C. taitungensis and C. revoluta in the Ryukyu Archipelago and Taiwan, diverged recently with continuous gene flow, resulting in a reciprocal paraphyletic relationship. Their previous evolutionary inferences are questioned from few genetic markers, incomplete sampling, and incomprehensive morphological comparison by a long-term taxonomic misconception. By whole range sampling, this study tests the geographic mode of speciation in the two species of Asiorientales by approximate Bayesian computation (ABC) using genome-wide single nucleotide polymorphisms (SNPs). The individual tree was reconstructed to delimit the species and track the gene-flow trajectory. With the comparison of diagnostic morphological traits and genetic data, the allopatric speciation was rejected. Alternatively, continuous but spatially heterogeneous gene flow driven by transoceanic vegetative dispersal and pollen flow with contrasting population sizes blurred their species boundary. On the basis of morphological, genetic, and evolutionary evidence, we synonymized these two Cycas species. This study highlights not only the importance of the Kuroshio Current to species evolution but also the disadvantage of using species with geographically structured genealogies as conservation units.

Fagaceae species predominate a diverse range of habitats in the northern hemisphere and are critical to the ecosystem and economy. The high morphological and genetic diversity of these species serves as the foundation for adaptation to environmental stress. To comprehend the diversity, an evolutionary viewpoint is required. However, we found extensive conflicts among gene trees at the genus level, resulting in inconclusive phylogenetic inferences based on various genetic markers. Unresolved phylogeny would affect taxonomy, biogeographic inference, and ancestral state. In this study, we aimed to look deeply into the source of phylogenetic discordance in Fagaceae. We sampled 65 species from six genera (Fagus, Lithocarpus, Quercus, Castanea, Castanopsis, and Notholithocarpus) and obtained 603,809 SNPs from transcriptome sequences. In addition to concatenated and coalescence-based approaches for phylogenetic inference, we also reconstructed 256 gene topologies to investigate conflict among nuclear genes. Our results show that the conflicts arise mainly from the relationship between Lithocarpus and Quercus, with approximately 34% of genes supporting the two genera as a sister group. We also try to understand why the genes of minority topologies are different from those of majority topologies. To answer the question, we performed a functional enrichment analysis to determine the function of the minority topological genes. According to the GO terms, their functions are primarily related to cellular structure or organelle. In the following step, we will investigate whether the main sources of discordance are introgression, incomplete lineage sorting, or selection.

Abstract Background Divergent genetic responses to the same environmental pressures may lead sympatric ecological speciation possible. Such speciation process possibly explains rapid sympatric speciation of island species. Two island endemic ginger species Zingiber kawagoii and Z. shuanglongensis was suggested to be independently originated from inland ancestors, but their island endemism and similar morphologies and habitats lead another hypothesis of in situ ecological speciation. For understanding when and how these two species diverged, intraspecific variation was estimated from three chloroplast DNA fragments (cpDNA) and interspecific genome-wide SNPs and expression differences after saline treatment were examined by transcriptomic analyses. Results Extremely low intraspecific genetic variation was estimated by cpDNA sequences in both species: nucleotide diversity π = 0.00002 in Z. kawagoii and no nucleotide substitution but only indels found in Z. shuanglongensis. Nonsignificant inter-population genetic differentiation suggests homogenized genetic variation within species. Based on 53,683 SNPs from 13,842 polymorphic transcripts, in which 10,693 SNPs are fixed between species, Z. kawagoii and Z. shuanglongensis were estimated to be diverged since 218~ 238 thousand generations ago (complete divergence since 41.5~ 43.5 thousand generations ago). This time is more recent than the time of Taiwan Island formation. In addition, high proportion of differential expression genes (DEGs) is non-polymorphic or non-positively selected, suggesting key roles of plastic genetic divergence in broaden the selectability in incipient speciation. While some positive selected DEGs were mainly the biotic and abiotic stress-resistance genes, emphasizing the importance of adaptive divergence of stress-related genes in sympatric ecological speciation. Furthermore, the higher proportional expression of functional classes in Z. kawagoii than in Z. shuanglongensis explains the more widespread distribution of Z. kawagoii in Taiwan. Conclusions Our results contradict the previous hypothesis of independent origination of these two island endemic ginger species from SE China and SW China. Adaptive divergent responses to the stress explain how these gingers maintain genetic differentiation in sympatry. However, the recent speciation and rapid expansion make extremely low intraspecific genetic variation in these two species. This study arise a more probable speciation hypothesis of sympatric speciation within an island via the mutation-order mechanism underlying the same environmental pressure.

The renewal of temperate coniferous forests has a high impact on the global climate, as well as the survival of forest wildlife. As an important native afforestation tree species in northern China, Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) is facing the dilemma of severe regeneration and forest growth. External factors, such as natural disturbances or human intervention, may affect the forest growth potential. Therefore, the present study explores whether environmental factors and afforestation methods affect the growth increment of Mongolian pine. To answer the question mentioned above, natural forest and two kinds of afforestation forests are included in this study. The growth increment is calculated by measuring basic growth parameters. A linear mixed-effect model is used to test whether surface fire, accompanying birch, edge effect, afforestation method, and tree age were determinants of the growth increment. With the model selection, the tree age combined with fire or afforestation is determined as significant effects on the growth increment. The effects of growth position and accompanying plants only influenced young pines. The effects decrease with age, implying the resource competition occurs at young ages only but not affect the adults of dominance trees. Since the growth rate of Mongolian pine varies with age, the environmental selection of timber volume is age-dependent. However, we also found that the growth increment slowdowns if too-fast growth investment in secondary growth at a young. Strengthening the competitive pressure of seedling afforestation is conducive to selecting individuals with a high growth increment and delayed growth cessation. Accordingly, fast-growing trees that survive fires are recommended as sources of seed-harvesting mother trees. Sowing afforestation that is easier to adjust the growth rate of seedlings is recommended than the seedling afforestation. Since external disturbances underlie the age-dependent selection of Mongolian pine growth, competition and environmental pressures at a young age are beneficial for prolonging the growth period and increasing timber volume accumulation. From this study, it can be seen that moderate fire disturbance and the selection of seed from healthy trees for tending are beneficial to the regeneration of temperate coniferous trees and the maintenance of healthy forests.

Hybridization frequently occurs in plant species. With repeated backcross, the introgression may influence evolutionary trajectories through the entry of foreign genes. However, the genetic admixture via hybridization events is often confused with the ancestral polymorphism, especially in closely related species that have experienced similar evolutionary events. In Taiwan, two independent-originated endemic snakebark maples have contrasted postglacial range expansion routes: northward and upward expansion in Acer caudatifolium and downward expansion in A. morrisonense. The range expansion causes the current parapatric distribution, increasing the possibility of introgression. This study elucidates how their genetic variation reflects introgression and historical demography. With 17 EST-SSR markers among the intensely sampled 657 individuals, we confirmed that the genetic admixture between species mainly was attributed to recent introgression instead of common ancestral polymorphism. The secondary contact scenario inferred by approximate Bayesian computation suggested that A. morrisonense received more genetic variations from A. caudatifolium. Introgression occurred in colonized Taiwan around the early Last Glacial Period. Furthermore, the demography of A. caudatifolium was more severely affected by introgression than A. morrisonense, especially in the wavefront populations with high altitude range expansion, implying an altitude-related adaptive introgression. In contrast, A. morrisonense exhibited ubiquitous introgression independent of postglacial expansion, suggesting that introgression in A. morrisonense was neutral. In terms of different genetic consequences, introgression had different demographic impacts on species with different altitude expansion directions even under the same climate-change conditions within an island.

Under climate fluctuation, species dispersal may be disturbed by terrain and local climate, resulting in uneven spatial-genetic structure. In addition, organisms at different latitudes may be differentially susceptible to climate change. Here, we tracked the seed dispersal of Acer caudatifolium using chloroplast DNA to explore the relationships of terrain and local climate heterogeneity with range shifts and demography in Taiwan. Our results showed that the extant populations have shifted upward and northward to the mountains since the Last Glacial Maximum. The distributional upshift of A. caudatifolium is in contrast to the downward expansion of its closest relative in Taiwan, A. morrisonense. The northern populations of A. caudatifolium have acquired multiple-source chlorotypes and harbor high genetic diversity. However, effective gene flow between the north and south is interrupted by topography, geographic distance, north-south differences in October rainfall, and other climate heterogeneities, blocking southward genetic rescue. In addition, winter monsoon-driven rainfall may cause regional differences in the phenological schedule, resulting in adaptive effects on the timing of range shift and the genetic draft of chlorotype distribution. Terrain, distance, and local climate also differentiate the northernmost populations from the others, supporting the previous taxonomic treatment of Acer kawakamii var. taitonmontanum as an independent variety.

Species delimitation may be difficult for recently divergent species, particularly those with few distinguishable morphological characteristics. Zingiber kawagoii and Z. shuanglongensis are two recently divergent species endemic to Taiwan whose extremely similar vegetative characteristics hinder their distinction during non-flowering seasons. Given their recent divergence, the speciation process and introgressions between these two gingers warrant exploration. However, such studies are hampered by the absence of appropriate molecular markers. To solve this dilemma, we developed 20 transferable expressed sequence tag-simple sequence repeat loci (EST-SSR). Seven highly differentiated loci were further identified for rapid species delimitation. A preliminary test using discriminant analysis of principal components (DAPC) validated the effective discrimination of these EST-SSR loci, while Bayesian clustering analysis (BCA) revealed obvious introgression events between species, particularly on positive-outlier loci. These results imply adaptive introgressions between these species. However, more sampling and further experiments are necessary to validate this inference and resolve questions regarding the introgression and speciation mechanisms. The development of genetic markers in this study provides appropriate experimental conditions and a basis for further research. [ABSTRACT FROM AUTHOR]