Tropical biomes today occupy a disjunct distribution around the equator covering about 7% of land surface, but harbouring more than 40% of plant species. This mystery is a fascinating topic yet to be fully addressed. We attempt to solve this mystery using our knowledge on the origin and migration of tropical gingers across these global biomes.
Above: Upper: Fossil records from Cretaceous (star, dot, polygon and square) to Pliocene (cycle) and pantropical distribution of Zingiberaceae. solid arrows indicate ancient dispersal and dotted arrows represent dispersal of young clades. Lower: Divergence and representatives of four subfamilies in Zingiberaceae. From left to right are Siphonochilus kirkii of Siphonochiloideae (photo credit: Smithsonian Botany Research Greenhouses), Tamijia flagellaris of Tamijioideae (photo credit: Axel Poulsen), Roscoea tibetica (Zingiberoideae) (photo credit: Jian-Li Zhao) and Etlingera yunnanensis of Alpinioideae (photo credit: Qing-Jun Li).
The position of continents and environments on Earth are ever-changing. The changes are most conspicuous on a million-year time scale, such as the shifts of the Indian Plate and tropical biomes. In many cases niche conservatism promotes species to track environmental changes. With the development of new statistical models and methods, the integration of phylogenetic reconstructions based on DNA sequence data with accurate fossil records provide a logical and repeatable way to reveal biogeographical history. The thousands of records from fossils and rock strata now provide a clear framework for understanding shifts of climatic zones, continental plates, and global climate patterns, and have facilitated our research on the associations of biome shift with plant evolution.
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Zhao, J-L, Yu, X-Q, Kress, W. J., Wang, Y-L, Xia, Y-M & Li, Q-J (2022). Historical biogeography of the gingers and its implications for shifts in tropical rain forest habitats. Journal of Biogeography, 49, 1339-1351. https://doi.org/10.1111/jbi.14386.
Tropical herbs are an indispensable and prominent component of tropical rain forests. However, fossil records of tropical herbs are far less common than the records of woody plants. The discovery of a few herbaceous fossils have provided powerful support to understanding the origin of tropical biomes in space and time. The Zingiberaceae (gingers and close relatives) is a pantropical monocot family of herbs. Its current distribution overlaps quite closely with the distribution of tropical biomes around the world. Our team and colleagues, who have been engaged in the study of gingers for some time, have found that the geographic distribution of fossils in this family is very different from the distribution of extant members. It is not surprising that the positions of fossils are only found in past tropical zones. This evidence suggested to us that the origin and dispersal of tropical biomes could be better understood by tracking the evolution of the ginger family.
We found that gingers originated in the north of Africa and then dispersed to paleotropical Asia by the Ark of the Indian Plate. Gingers in Malesia were derived from Indo-Burma rather than the opposite from Malesia to Indo-Burma. Also, some young clades of gingers in Africa and India came from the paleotropics. Our study provides an exciting story in understanding the origin and dispersal of tropical biomes and extends our knowledge on the source of paleotropical biomes in Malesia.
Interestingly, the out of Indo-Burma dispersal has several routes. Besides the southern migration to Malesia, another route is the migration north into the Himalayas and the Hengduan Mountains, and then diversification with the orogeny caused by the collision between the Indian and Eurasian Plates. These mountainous taxa, such as Roscoea, provide good models to explore the origin of hyperdiversity in many biodiversity hotspots.
Jian-Li Zhao, Associated Professor, Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology and Institute of Biodiversity, School of Ecology and Environmental Science, Yunnan University, Kunming, China
Qing-Jun Li, Professor, Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology and Institute of Biodiversity, School of Ecology and Environmental Science, Yunnan University, Kunming, China
W. Kress John, Curator Emeritus, Department of Botany, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
@Jian-Li Zhao / http://www.sees.ynu.edu.cn/info/1015/1879.htm
@ Qing-Jun Li / http://www.sees.ynu.edu.cn/info/1014/1100.htm
@ John Kress / https://naturalhistory.si.edu/staff/john-kress