No colony is an island or a remote patch on sea ice on the coast of Antarctica. Emperor Penguins move all around the frozen continent making one single interbreeding population for the whole species. A single circumpolar population! Even though fidelity for the natal site is calling most of the individuals back to mate and rear their chicks in the colony they were born, a constant dispersal every generation is producing the fully admixed genetic pattern found by Cristofari and co-authors and published in prestigious journal Nature Communications this week.
"Our data also suggest that when a colony location is suddenly wiped out by a catastrophic event, as it happened following the calving of the Mertz Glacier, all the individuals have at once to find another good breeding spot" says Dr. Céline Le Bohec, from the CNRS-UniStra and the Centre Scientifique de Monaco, senior author in the study and leader of one of the programme of the French Polar Institute Paul-Emile Victor (IPEV). Through an international collaborative work between Norway, Italy, USA, UK, Germany, Austria, France and Monaco, researchers employed a vast genomic dataset to reconstruct the genetic structure of the species and estimate the migration rate among six colonies of Emperor Penguins, some of which separated by 8000 km of coast line. When they leave the natal colony for the first time, juveniles spend two-three years, mostly at sea, before attempting to reproduce.
From direct survey of the colony of Dumont D'Urville (Pointe Géologie, Terre Adélie), we realized that between 15 to 20% of them never come back. Besides some that don't make it, now we know that around 5% of all juveniles find a new colony to join. In some cases, researchers observing a sudden decrease in colony population size often explained it by high mortality linked to harsh environmental conditions during a given year. Massive dispersal can now also be considered as an 0alternative explanation.