By Sankar Subramanian, Griffith University
This article was originally published at The Conversation. Read the original article.
There are now 18 recognised species of penguins. All live predominantly in the Southern Hemisphere (those Galapagos penguins being the exception), in a wide range of climates.
The habitats of modern penguins can be grouped into four climate zones. The Galapagos penguin (Spheniscus mendiculus) lives in a tropical habitat and two other species, the Peruvian penguin (S. humbolti) and the Black–footed (S. demersus) live in the subtropical regions.
The remaining eight species of penguins - the Fiordland, Snares, Erect-crested, Royal, Yellow-eyed, Magellanic, White-flippered and Little Blue penguin - live in temperate regions of the world.
Where penguins live can tell us something about how they are related. We can also look at fossils. Fossil penguins have been recovered from a range of latitudes in the Southern Hemisphere - from New Zealand to Peru. The earliest penguin-like fossil is 59-61 million years old, but fossils related to living penguins are very recent, less than 10 million years.
Another method is to use DNA sequences extracted from blood samples of living penguins. Previous studies using this molecular method gave ages much older than those based on morphological data.
Morphological and molecular methods have different limitations and uncertainties. That means to determine the actual age of the penguin ancestor, we need to use both.
We obtained blood samples from 11 penguin species belonging to all six groups (genera) of penguins living in four distinct climates. We then extracted DNA sequences from these samples through standard molecular biological techniques. We analysed the sequences using computational methods to examine how different penguins are related. Finally we used sophisticated analytical software to precisely estimate the age of the penguins' ancestor. Our analysis suggests the ancestor of all modern penguins lived 20 million years ago, much younger than previous molecular studies.
Our analysis also showed that the major penguin lineages diverged around 10-15 million years ago. What can this tell us about penguin evolution?
Interestingly Antarctica saw rapid cooling around the same time - 10-15 million years ago. At this time Antarctica developed a permanent ice cap that covered the entire continent. We connected these two dots and speculate that there might be connection between the rapid cooling of the Antarctic and the divergence of the penguin lineages.
Although we don’t have any proof for this connection, it’s a fascinating idea that adds to what we know about evolution and how past climate change has affected species.
Sankar Subramanian received funding from the ARC and the Australia-India Strategic Research Fund.
Was penguin evolution driven by a cooling Antarctic? by Sankar Subramanian, The Conversation, 13 November 2013