King Penguins and Ice Ages
King Penguins and Emperor Penguins share a similar appearance. In fact, the poor King Penguins in the Central Park Zoo are called Emperors by roughly 99% of the visitors I have overheard talking about them (also overheard: one child told his mother than penguins definitely know about Captain America). Yet, Kings and Emperors have very different environmental preferences. Whereas Emperors breed on sea ice sheets, Kings require sites that are ice-free year-round to carry out their unique breeding cycle, which spans over a year from egg-laying to fledging of the juveniles.
A recent study by Dr. Emiliano Trucchi and colleagues looked at the genetic structure of Kings from Possession Island. Possession Island is part of the Crozet Archipelgo in the Indian Ocean, where roughly half of the world’s population of King Penguins lives. These data revealed that the population in this region was very low about 20,000 years ago.
Why might this be? At 20,000 years before present, the Earth was locked in a cold period known as the Last Glacial Maximum (often referred to as the Ice Age). In North America glaciers extended right down to New Jersey. In the Southern Hemisphere, winter sea ice extended far north of the modern day limits, enveloping many islands that stand in open water all year round today, including Possession Island. This would presumably make it impossible for King Penguins to successfully breed on many of the islands they favor today. So what happened to all those penguins? One possibility raised by the authors is that they moved North to ice-free beaches in places like New Zealand. This hypothesis is supported by a few tantalizing fossils that suggest Aptenodytes penguins once occurred in New Zealand (and maybe even South Africa).
As climate warmed and sea ice retreated, King Penguins were able to reclaim sites like Possession Island as breeding colonies. This led to a marked increase in the Crozet archipelago population, as shown by the DNA analyses. While it may seem like this particular group of penguins benefited from melting ice 20,000 years ago, playing the warming tape forward raises a troubling specter. Other studies have shown reproductive rates in the modern Crozet Archipelago King Penguin populations have been negatively impacted by increased sea temperatures because warmer temperatures force the penguins to swim farther from their nests to find food-rich cold waters, requiring more energy use and increasing the time at sea.
Trucchi E, Gratton P, Whittington JD, Cristofari R, Le Maho Y, Stenseth NC, Le Bohec C. 2014 King penguin demography since the last glaciation inferred from genome-wide data. Proc. R. Soc. B 281: 20140528.