Photographs of some of the Hedychium spp. Picture Credits: (C) Ajith Ashokan, TrEE Lab
Researchers from the Indian Institute of Science Education and Research, Bhopal, have explored how the diverse species of ginger lily (Dolan champā in Hindi) have arisen as observed today from their ancestors through changing geographical and climatic factors in India and neighbouring countries. Based on analysis of DNA sequences, they show that the uprising of the Himalayas and the origin of the monsoon in the Indian subcontinent have majorly influenced how these lilies diversified into many species that were then able to colonise different places near and far. They found that ginger lilies may have originated in the northern Indo-Burma region and have spread to other parts of the world, including northeastern India and the Western Ghats. The study was published in Molecular Phylogenetics and Evolution.
Studying organisms of the past and present and the relationships between them help researchers understand why and how animals and plants are so diverse. The diversity of plants is important as it ensures a variety of plant products, controls erosion, regulates pests and pathogens and keeps the soil fertile.
Ginger lily is a flowering plant that bears sweet-smelling white flowers. Several species of the plant are found in the northeast-Indian states of Meghalaya, Manipur and Nagaland, Southwest China and Northern Thailand. However, only six species are found in the Western Ghats of India. To understand the origin and diversity of the ginger lilies, researchers collected plant samples from the Himalayas, Myanmar, China and the Malay archipelago (the largest group of islands near Indonesia and the Philippines), and also from the herbariums and museums from different parts of the world. They obtained DNA sequences from these samples. Using bioinformatics, they constructed a diagrammatic representation of evolutionary relationships (phylogenetic tree) between different species of ginger lilies worldwide.
The phylogenetic tree showed that ginger lilies originated in the Indo-Burma region and then dispersed to neighbouring countries. It also showed that ginger lilies originated as early as 19 to 18 million years ago. However, it underwent explosive speciation in Meghalaya and Indo-Burma only around 3 to 2 million years ago. This period, when several different species of ginger lily evolved in a short period, coincides with the intensification of the upliftment of the Himalayas.
The multistage uplifts of the immense Himalayan mountain range began to form between 50 to 40 million years ago when the Indian tectonic plate collided with the Eurasian plate and continued to thrust into it. The collision and uplift resulted in significant climate changes and new geophysical environments. It resulted in the start of the monsoon system in Asia and the seasonality in rainfall. However, the monsoon strengthened between 15 to 4 million years ago.
When a species diversifies within a short period compared to its long uneventful evolution, many branches are seen as a group in the phylogenetic tree.
“We can observe that many new species originated around a time that corresponds to when the Himalayan uplift intensified,” says Dr Ajith Ashokan, the first author of the paper.
In any given environment, the functional role of an organism in an ecosystem is called a niche. For example, the niche of fungi is to decompose dead material. Dr Vinita Gowda, head of the current research team, says, “The upliftment of the Himalayas resulted in creating new environments. These environments, in turn, created and opened more ecological niches which forced species to adapt to these new environments, evolving into different species.”
The Himalayas also formed physical barriers isolating populations. Isolated populations may evolve to become different species. Additionally, the eastern Himalayas show a high diversity of ginger lilies because many species arrived from the neighbouring Indo Burmese region.
The origin of the monsoons may also have had an important role to play in diversifying these plants.
“Ginger lilies like humidity and are found in the wet tropics of India and Asia. As the Asian monsoon intensified, there were more moisture-rich days for these plants to thrive and propagate. It also probably helped them diversify rapidly in northeast India,” says Dr Gowda.
The Eastern Himalayas experience more rainfall (annual average rainfall of 3800–4000 mm), whereas the western Himalayas are much drier with an annual average rainfall of 75–150 mm. This difference in rainfall may have caused ginger lilies to evolve into different species to populate these very different habitats.
The occurrence of semi-arid regions in both Central and Northern India due to the land becoming drier over time acted as barriers to spreading species from Indo-Burma and the Himalayas into Southern Peninsular India. As a result, we find only about six species of ginger lily in the western ghats.
Ginger lilies in the Malay Archipelago are epiphytes (plants growing on other trees) and have small stature. The researchers find that this epiphytic character and small stature may have been characters first seen in ancestral Ginger Lilies from several million years ago. These characters may have evolved to avoid getting submerged with the soil when fluctuating sea levels cause flooding. Growing on a tree enables the ginger lily to avoid death when the ground gets submerged.
Thus, today’s diversity in ginger lilies results from many geographical and climatic factors such as uplifting of the Himalayas, monsoon, aridification and changing sea levels. These have played a significant role in the diversity and distribution of the Ginger Lily that we see today. Researchers stress the importance of studying the diversity of plants at the global level to understand the current diversity. This study led by Dr Gowda is a collaborative effort with botanical gardens and natural history museums across different countries. Just like the present study, the evolutionary and biogeographic history of an organism needs to be constructed not only on a widespread geographical scale covering many countries but also across a geological time scale to understand the complete story.
Currently, the highly diverse regions of Indo-Burma and Borneo forests are under threat due to deforestation. These regions are the hotspots of diversity for ginger lily and many other species. Commenting on the implications of this study, Dr Gowda says, “From a conservation perspective, the effect of rapid climate change events along with loss of habitat in the northeastern region (of India) can prove to be fatal to the gingers and many other plant species that we study”. If some species in some regions in their distribution get extinct due to human-caused reasons, such as urbanisation and plantations, then we miss out on crucial puzzles in the complete story of how that particular group evolved.
This article has been run past the researchers, whose work is covered, to ensure accuracy.