Tracing the evolution of the aubergine

The aubergine is an economically important plant in Asia and Africa, but little is known about how it evolved. Historical documents and genetic data show that the plant was first domesticated in Asia, but most of its wild relatives are from Africa.

Researchers from the Museum and the University of Helsinki have now discovered that a single event gave rise to two distinct lineages of the plant. One is an African group of species and the other is the wild forerunner of the domesticated aubergine, also known as the eggplant.

In a study published in the American Journal of Botany, researchers sequenced the DNA of the aubergine and 22 species directly related to it.

First author of the paper, Xavier Aubriot, says, 'Nearly all species of the group of the eggplant live in low land savannahs and more or less arid habitats, and some species are very widespread across Africa. Our results suggest that there had been a dramatic expansion of the distribution range of the group over the last two million years.'

Domesticating the aubergine

The aubergine (Solanum melongena) is a member of the giant genus Solanum (containing around 1,400 species) within the nightshade family (Solanaceae). Aubergine is one of the most economically important solanaceous crops, along with potatoes, tomatoes, peppers, and tobacco.

It is now a domesticated plant. Humans started to domestic plants thousands of years ago, and since then we have relied on them for food, medicine, clothing and construction.  Development of the first civilisations relied on a relatively small number of domesticated and cultivated plants including wheat, rice or potato. Many of these species are now cultivated across the globe, and scientists are using new tools to untangle their histories.

Previous studies have shown that the aubergine was first domesticated somewhere in China and India. However it is only recently that taxonomists have resolved the status of the wild species that are related to the cultivated aubergine. Many of them are found in the savannahs of Africa.

Dr Sandra Knapp, a researcher at the Museum, is part of a team of botanists, entomologists and data specialists from the Museum who are seeking out and mapping the distribution of wild species related to tomatoes and potatoes.

She says, 'Understanding the evolutionary history of a group depends upon detailed research using the collections of museums like the Natural History Museum. Resolving the identities of the wild species allows us to work out where they occur, which then allows us to dig deeper into the factors that determine their current status.'

The team found that the group containing the relatives of the aubergine originated in northeastern Africa some two million years ago.

Plants then dispersed eastwards to tropical Asia, and to southern and western Africa. In Asia, the dispersal gave rise to a species that scientists call Solanum insanum. It is from populations of this wild species that the aubergine was later domesticated.

Researchers were surprised to find that the dispersion of the group to Asia seemed to result from a single dispersal event rather than a linear series of distinct stages.

Aubergines in Africa

Some of the African wild relatives of the aubergine have extremely wide distributions. Solanum campylacanthum can be found all along the eastern part of the continent, from Kenya to South Africa. Experts think this is down to how the seeds are dispersed.

The African elephant and the impala both live on African savannahs and roam widely. They also both eat the fruits and disperse the seeds of wild aubergine relatives.

That means that if today the range of African elephants is drastically reduced due to human activities, wild aubergine relatives may suffer as well.

Xavier Aubriot adds, 'This study is actually a first step for deeper analyses. Many important questions remain to be investigated - how did the eggplant group reach tropical Asia? Were there interactions between early humans and wild eggplant relatives? What factors were involved in the domestication process of the eggplant from its wild progenitor, Solanum insanum?

'We are now working on getting a much improved sampling and new sources of data to shed more light on the complex and interesting origin of the eggplant.'