Abstract
The karst environment is characterized by low soil water content, periodic water deficiency, and poor nutrient availability, which provides an ideal natural laboratory for studying the adaptive evolution of its inhabitants. However, how species adapt to such a special karst environment remains poorly understood. Here, transcriptome sequences of two Urophysa species (Urophysa rockii and Urophysa henryi), which are Chinese endemics with karst-specific distribution, and allied species in Semiaquilegia and Aquilegia (living in non-karst habitat) were collected. Single-copy genes (SCGs) were extracted to perform the phylogenetic analysis using concatenation and coalescent methods. Positively selected genes (PSGs) and clusters of paralogous genes (Mul_genes) were detected and subsequently used to conduct gene function annotation. We filtered 2,271 SCGs and the coalescent analysis revealed that 1,930 SCGs shared the same tree topology, which was consistent with the topology detected from the concatenated tree. Total of 335 PSGs and 243 Mul_genes were detected, and many were enriched in stress and stimulus resistance, transmembrane transport, cellular ion homeostasis, calcium ion transport, calcium signaling regulation, and water retention. Both molecular and morphological evidences indicated that Urophysa species evolved complex strategies for adapting to hostile karst environments. Our findings will contribute to a new understanding of genetic and phenotypic adaptive mechanisms of karst adaptation in plants.
Highlights
Environmental heterogeneity is one of the most important factors influencing evolutionary trajectories and ecological adaption of species (Allouche et al, 2012)
The two species all flower in the winter, and in field observations and laboratory experiments, we found that U. rockii and U. henryi can not survive outside the karst limestone, which indicated that the karst limestone plays a significant role in their growth and development
Single-copy genes were extracted for phylogenetic analysis, and by positive selection analysis and function annotation, we aimed to investigate the potential mechanisms of how these two-species adapted to the karst environment
Summary
Environmental heterogeneity is one of the most important factors influencing evolutionary trajectories and ecological adaption of species (Allouche et al, 2012). The ecological environment in karst region is extremely hostile, plant communities in this region exhibit remarkably high levels of species richness and endemism and make a large contribution to the floristic diversity of China (Gao et al, 2015; Hao et al, 2015; Feng et al, 2020). This region possesses various ecological niches afforded by complex terrains (e.g., fissured cliffs and extensive caves) and variable climatic and edaphic conditions (Hao et al, 2015). Such information is important for understanding the survival and adaptive strategies of species in the special karst environmental conditions
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