Authors: Kyalo, Cornelius M.; Chen, Ling-Yun; Lema, Mathias; Malombe, Itambo; Hu, Guang-Wan; Wang, Qing-Feng
Publication: Journal of Systematics and Evolution
Year: 2020
Genera: Saintpaulia, Subgenus Streptocarpella

Streptocarpus ionanthus (Gesneriaceae) is endemic to Tanzania and Kenya, distributed in Tanga, Morogoro, and Kilifi regions. The species houses nine subspecies characterized by complex morphotypes and poorly understood evolutionary relationships, and thus is an ideal model for investigating evolutionary dynamics over time. Using multiple methods, we sought to test our hypothesis that the infraspecific taxa in Strionanthus are slightly variable and evolving populations. We first examined the genetic diversity, population differentiation, and phylogeographic structure among the populations of Strionanthus using both chloroplast and nuclear markers. We then estimated the divergence time of Strionanthus lineages and modeled past and future distribution. Despite Strionanthus exhibiting bottleneck events across its range, the populations maintain relatively high genetic diversity attributed to historical population admixture or local adaptation arising from habitat heterogeneity. The phylogeographic and genetic structure revealed a high connection among the Usambara mountains populations, while molecular dating suggested most diversification of haplotypes began ~1.32–0.18 million years ago and intensified toward the present, a conclusion of recent diversification. Phylogenetic relationship of Strionanthus cpDNA haplotypes revealed five main lineages with unique haplotypes that could be suggestive of past isolated refugia during the Pleistocene climate shifts. According to niche modeling, the stability of suitable areas during the Last Glacial Maximum (LGM) offered protective micro‐habitats that have preserved the genetic diversity of Strionanthus to date. In conclusion, our findings suggest a complex Strionanthus with slightly variable lineages or populations attributed to multiple refugia and on the verge of divergence.