EPOW - Ecology Picture of the Week

Lava Lizard Radiation

Lava Lizards (Microlophus spp.), Family Tropiduridae
Galapagos Islands, Ecuador

Explanation:  This week's rather busy presentation illustrates the interesting suite of small lizards that occur across the Galapagos Islands that are part of, and off the coast of mainland, Ecuador, South America.

The Galapagos Islands are, of course, more famous for its diversity of so-called "Darwin's finches," an array of some 13 species of birds with diverse bill structures and ecologies, that evolved from an initial finch immigrant.  However, these islands also hold other striking examples of species that have undergone such evolutionary divergences ... such as the lava lizards of genus Microlophus which evolved from an original lizard that colonized the islands from mainland South America.  

The process of species splitting from some initial "founder" is called "adaptive radiation" (which has nothing to do with ionizing radiation).  On the Galapagos archipelago, lava lizards have radiated (evolved) into no less than seven individual species, four of which are presented in this week's EPOW photos that illustrate examples from specific islands.  

In general, the lizards that live on dark lava appear darker in coloration, and males generally appear darker than females which have red cheeks at maturity. 

But there is additional variation within and among these species in color, pattern, and body size.  For example -- as shown in the above photos -- the Galapagos lava lizard (Microlophus albemarlensis) appears gray with black speckles on Bartolome Island, more dull gray on Fernandina Island, dark gray with light gray lateral stripes on Isabela Island, and sports bright white racing stripes on Santa Cruz Island.  Variation in appearance among the islands might be examples of genetic drift in isolated populations, and might signal early stages of eventual, further speciation.  

Lava lizards in turn belong to the diverse family Tropiduridae, once considered a subfamily of Iguanidae.  Tropidurid lizards consist of an amazing set of over 280 species in 9 genera found in South America, the Galapagos, and the West Indies.  

Additionally, as seen in a previous EPOW episode, lava lizards are part of a broader set of species that perform cleaner functions on the Galapagos Islands by snatching insects from the bodies of larger animals.  

The Galapagos Islands are truly an amazing natural laboratory!