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A research journey from jungles to genomes

As the small propeller plane came in towards the airstrip, we could see the flat plains stretching away ahead of us, and the forested slopes of the Andes passing below. This was Villa Garzón, in the province of Putumayo, a remote corner of Colombia with a turbulent history. Until recently the Amazonian fields and forests stretching ahead of us were prime cocaine growing territory, and largely controlled by the FARC guerilla group—definitely not recommended for tourists or biologists alike. However, the recent peace accord signed in Colombia between the government and the FARC offered a new hope for peace across the country, as well as an opportunity for adventurous biologists to visit previously inaccessible parts of the country.

One of the goals of our trip was to search for a butterfly called Heliconius tristero (or Heliconius timareta tristero as it is now more correctly known), which had been described in 1996 from just two specimens collected in this area. Almost anyone who has visited the jungles of tropical America is likely to be familiar with the ‘postman’ or Heliconius butterflies. With their slow flight, brilliantly coloured patterns and long rounded wings, they are a prominent and highly visible member of the jungle community. They are generally well studied, so it was unusual to find a new species, and especially one known from so few individuals. Only one biologist had successfully collected this species since, and we were hoping to confirm its existence.

Image provided by the author. Used with permission.

So, after checking into our hotel in the town of Mocoa, we soon headed out into the nearby mountains in search of tristero. And after a short hike into the forest, we were rewarded almost instantly. Our Colombian collaborator Mauricio Linares was the first to get lucky, but soon we had netted several specimens. A few were preserved for genetic analysis, the remainder carefully kept alive in order to establish a population in the laboratory for future studies. It turns out that tristero is not that rare once you can get to the right place. Peace in Colombia, probably the most biologically diverse nation in South America, is a good thing for biologists as well as everyone else in this remarkable country.

What is surprising about tristero is that it is a remarkably close mimic of its close relative, Heliconius melpomene. Indeed, one reason why the species had remained hidden until 1996 was not just its inaccessible home, but also the fact that it was only recognized as a distinct species from its close relative melpomene using DNA evidence. Heliconius are famous for this mimicry – different species evolve similar wing patterns to tell predators that they are poisonous to eat. ‘Stay away from us’ these species are signaling – we are all packed with toxins. Different species benefit from sharing a pattern by sending a common signal of their nastiness to predators. In Heliconius, most mimicry occurs between relatively unrelated species – distant cousins if you like, rather than brothers and sisters. Tristero was the first of a series of populations recently discovered along the eastern edge of the Andes in which there is mimicry between very close relatives. However, although it was the first to have been discovered, tristero remains the least well studied of these populations due to the inaccessibility of the Putumayo region.

Image provided by the author. Used with permission.

Despite their recent discovery, these butterflies found in remote Andean valleys have rapidly become evolutionary celebrities. It turns out that they have evolved mimicry by a rather sneaky means. Mostly we think of evolution as occurring through the chance process of mutation generating random changes, followed by exhaustive winnowing of these (mostly harmful) mutants by natural selection. What if a population could bypass this rather tiresome process of sorting through random errors to find adaptive genetic variants? It turns out that these butterflies have done just that, by borrowing genetic material from their close relatives. Occasional mistakes in choosing mates mean that closely related species occasionally produce hybrids, and these rare hybrid individuals can provide a route for genetic exchange between species. This allows genes for wing patterns to move between species, leading to the rapid evolution of mimicry.

These discoveries have relevance to our own species. It turns out that humans, much like the butterflies, have also acquired genetic material from close relatives, in this case our now extinct cousins the Neanderthals. This genetic material has helped people live in extreme environments such as the high mountains of the Himalayas, and may have a role to play in genetic disease. The study of butterflies from remote corners of the world has helped to shed light on our own origins. These unexpected coincidences, the discovery of common processes across the diversity of life, provide an important motivation for biological research driven by pure curiosity. But in an increasingly globalized world, there is also just a thrill in exploring obscure corners of the globe where few biologists have travelled. Right now, we are sequencing the genomes of those tristero specimens collected in Colombia in January, and we will soon be able to confirm whether they acquired their gaudy colours in the same way.

Featured image provided by the author and used with permission.

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