Differentiation mechanism and evolution of the cryptic species Stellera chamaejasme L
The underlying premise in speciation biology is that population divergence is a crucial stage in evolutionary diversification (Harvey et al., 2017). If this is true, the population differentiation should be the impelling dynamics for cryptic diversity across time and space. It also suggests that population differentiation act as a rate-limiting constraint on speciation by influencing macroevolutionary processes (Harvey et al., 2017). However, speciation may be required to restrict the coexistence of differentiated populations in sympatry for the persistence of those populations (Dynesius and Jansson, 2014), the evolution of ecological divergence (Price et al., 2014), and reproductive isolation (Dobzhansky, 1951).
We focused on elucidating population genomics of polymorphic Stellera chamaejasme L. (Thymelaeaceae). Stellera chamaejasme (single species in the genus Stellera L.) is a perennial invasive shrub belonging to the Thymelaeaceae family (Zhang, 1999). This species has a wide geographic range extending from the western Himalaya (Nepal), north-western Yungui Plateau through the Hengduan Mountains north-westward to the Qinghai-Tibetan Plateau (QTP) platform and north-eastward to the plain of northern China, including Bhutan, Mongolia and Russia (Zhang et al., 2015; 2010). In the past, flower color polymorphism was only the basis for the delimitation of two separate species S. chamajasme and S. bodinieri H. Leveille (Leveille, 1912; Linnaeus, 1753) or two forms of species (Huang, 1985; Diels, 1912). These two flower color morphs are 1) white-red flower type, hereafter referred as S. chamaejasme f. chamaejasme, with a red calyx tube and white tube lobe flowers (vast distribution from western Himalaya, QTP to northern China, Mongolia, Russia), and 2) pure yellow flower, referred as S. chamaejasme f. angustifolia (Diels, 1912), with a yellow calyx tube and lobe (grows south from the Hengduan Mountains to the Yungui Plateau) (Zhang et al., 2010). The recent discoveries have increased the color morphs into four. In addition to the above two, others are white-yellow flower morph, with yellow calyx tube and white lobe (distributed in the south-eastern Hengduan Mountains), and pure-pink flower morph, with a pink calyx tube and lobe (distributed only in Yajiang county of the Hengduan Mountains).
Pleistocene glaciation advances the cryptic speciation of Stellera chamaejasme L. in a major biodiversity hotspot
Rana S.K., Rana H.K., Landis J.B., Kuang T., Chen J., Wang H., Deng T.*, Davis C.C.*, Sun H.*
Journal of Integrative Plant Biology (IF 11.4) (Early view)
https://onlinelibrary.wiley.com/doi/epdf/10.1111/jipb.13663?domain=author&token=AIHY5VVFMX2CUIHR8YAE
Summary
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The expansive Himalayan-Hengduan Mountains (HM) and Qinghai-Tibet Plateau (QTP) form a biodiversity hotspot imperiled by global change. The species diversity, resulting from myriad factors led to plant diversification from 10 million years ago till now. However, despite understanding speciation timing better, a lack of in-depth population-level studies and a dearth of organismal sampling among closely related species and populations leaves an incomplete view of diversification trends and biotic influences.
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We delve into the complex factors influencing diversification through genomic and eco-morphological analysis within the Stellera chamaejasme L. complex, known for its significant floral diversity.
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Our results uncover four cryptic species, indicating a more recent and younger diversification period (~2.67–0.9 Mya), driven by Pleistocene glaciation and a complex set of interacting biotic factors. These factors prompted allopatric speciation and advocated cyclical warming–cooling episodes along latitudinal and altitudinal gradients throughout the Pleistocene.
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The study emphasizes the existence of cryptic species within these mountains, broadening our understanding of species evolution to more recent than previously recognized. This novel perspective may reshape evolutionary paradigms in plant science. Additionally, it also brings to light concerns over future warming’s possible impacts on alpine species distribution and speciation, underlining the urgency for increased conservation efforts.
Population transcriptomic sequencing reveals differentially expressed genes as the basis for cryptic species morphs differentiation
Santosh Kumar Rana, Jacob B. Landis, Hum Kala Rana, Tao Deng, Hang Sun*
Manuscript in preparation
Progress:
The study aimed in using population transcriptomic sequencing to reveal differentially expressed genes as the basis for cryptic species morphs differentiation. The provided objective is based on the population level RNA-seq transcriptomic analysis for different cryptic morphs within Stellera chamaejasme. The detailed objectives are to:
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Detect the genes/genomic basis for differentiating the existing four cryptic species morphs.
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Infer the differentially expressed genes among the four different cryptic species morphs.
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Study the enriched pathway for the functionally annotated candidate genes.
We characterized the gene expression variation as the basis for population differentiation across the four intuitive cryptic species morphs of S. chamaejasme using RNA-seq population datasets. We used the pooled transcriptome libraries for Trinity de novo assembly and identified 507384 (PP morph), 427096 (YY morph), 370367 (YW morph), and 296855 (RW morph) differentially expressed genes. The comprehensive functional annotation based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway database (KEGG) revealed that these unigenes were mainly related to many physiological, metabolic, and molecular processes. Furthermore, the comparative transcriptome analysis indicated 1885 pathway genes that were primarily involved in ‘Plasma membrane’. The differentially expressed genes are present in varied numbers within the four morphs. Indeed, the up-and downregulated expressed genes characteristically differentiate four cryptic species morphs.
