J Syst Evol

• Research Articles •    

Multiple Pleistocene refugia and recent diversification for Streptocarpus ionanthus (Gesneriaceae) complex: Insights from multiple molecular sources

Cornelius M. Kyalo1,2,3 , Ling‐Yun Chen1,3, Mathias Lema4 , Itambo Malombe5 , Guang‐Wan Hu1,3* , and Qing‐Feng Wang1,3   

  1. 1 Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China
    2 University of Chinese Academy of Sciences, Beijing 100049, China
    3 Sino‐Africa Joint Research Center, Chinese Academy of Sciences, Wuhan 430074, China
    4 Tanzania Forest Services (TFS) Agency, P.O. Box 40832, Dar es Salaam, Tanzania
    5 East African Herbarium, National Museums of Kenya, P.O. Box 45166‐00100, Nairobi, Kenya
  • Received:2020-04-20 Accepted:2020-06-24 Online:2020-07-08 Published:2020-07-08

Abstract:

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 Str. ionanthus are slightly variable and evolving populations. We first examined the genetic diversity, population differentiation, and phylogeographic structure among the populations of Str. ionanthus using both chloroplast and nuclear markers. We then estimated the divergence time of Str. ionanthus lineages and modeled past and future distribution. Despite Str. ionanthus 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 Str. ionanthus 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 Str. ionanthus to date. In conclusion, our findings suggest a complex Str. ionanthus with slightly variable lineages or populations attributed to multiple refugia and on the verge of divergence.

Key words: diversification and evolution, genetic diversity, genetic structure, phylogeography, Streptocarpus ionanthus