Warm waters. Curious landscapes. Unique wildlife. These words are commonly used when people talk about Tropical oceanic islands. Sometimes, they are romantically described as “paradises on Earth”. Despite undeniable beauty, some of the most famous Tropical archipelagos (e. g. Galápagos, Hawaii) are volcanic, meaning that they have never been connected to the mainland. This makes them indeed a paradise, not only for tourists, but also for evolutionary biologists.
In an expedition to Fernando de Noronha oceanic archipelago in northeastern Brazil, a team of scientists lead by the PhD student Waldir Berbel-Filho and the Professor Dr. Sergio Lima from Universidade Federal do Rio Grande do Norte, were intrigued to find individuals of the widely spread South American guppy (Poecilia vivipara) inhabiting a local mangrove. Two questions came to their minds. Where did the guppies come from? How did they get to Fernando de Noronha?
To answer these questions, the scientists used DNA sequences of this brackish or freshwater species. Comparing the genetic information from the island and several continental populations, the researchers found that the isolated population represented a possibly exclusive genetic lineage, which is closely related to the geographically closest drainages on the continent.
However, how did the fish get into the island? Natural colonization? Human introduction? Both Fernando de Noronha and Natal (the closest continental city) served as American military basis during and post WWII period. Indeed, the militaries recommended to bring guppies to the island in an attempt to control mosquito larvae population. It would be reasonable to think that the fish was brought from the closest city around, matching the genetic results. However, it is never that easy. A potential natural dispersal of the fish into the island cannot be completely discarded. Guppies are famous due to its exuberant colours and shapes, but also for being resistant to a wide range of environmental conditions. In a scenario of favourable sea current, physiological tolerance, and a bit of luck, guppies may have managed to find their way to the island. Independently on how they got there, the authors argued that Fernando de Noronha guppy population represents a valuable example to understand how small populations manage to colonize and thrive in isolated environments.
Although being visited by thousands of people every year, some of the most intriguing secrets of Tropical oceanic islands may still be hiding on the DNA of their inhabitants. The “paradises on Earth” are simultaneously filling our hearts with beauty, and our minds with knowledge.
This was a text originally written to get published at science communication news service EurekAlert!
The curious case of the guppy across the ocean got a few press articles, check it out some nice ones at National Geographic and at SciTechDaily!
Image: The paradisiac Baía dos Porcos beach, Fernando de Noronha archipelago, Northeast Brazil.
Credit: Luciano Barros-Neto
Image: Mangrove in the Maceió microbasin, Fernando de Noronha archipelago, Northeast Brazil.
Credit: Liana Figueiredo