Record Details

Vitousek, Maren Noelani;Rubenstein, Dustin R;Wikelski, Martin
The evolution of foraging behavior in the Galápagos marine iguana: natural and sexual selection on body size drives ecological, morphological, and behavioral specialization
Lizard Ecology: The Evolutionary Consequences of Foraging Mode
Book Section
Stephen M. Reilly, Lance D. McBrayer, and Donald B. Miles
Cambridge University Press
Cambridge, UK
Amblyrhynchus cristatus
Each year thousands of tourists visit the Galapagos Islands and become intrigued by the unique habits of the world's only sea-going lizard, the Galapagos marine iguana (Amblyrhynchus cristatus), as it swims offshore and dives under the waves to feed. One of the islands' first visitors, Charles Darwin, reported fascination with watching these creatures forage, and he “opened the stomach of several, and in each case found it largely distended with minced sea-weed . . . [that] grows a t the bottom of the sea, a t some little distance from the coast.” (Darwin, 1839). We now know that the Galapagos marine iguana is the only terrestrial vertebrate that forages almost exclusively on macrophytic marine algae. Although marine iguanas are active foragers, their short, intense bouts of foraging activity more closely resemble the activity pattern of sit-and-wait foragers. To understand why these endemic lizards have adapted such a unique foraging strategy and how it differs from the general pattern of foraging in lizards, we must examine the social and environmental selective pressures that are unique to this species and its environment. The Galapagos marine iguana is a model system to understand how natural and sexual selection drive morphological and behavioral adaptations. In this chapter we will show how the unique foraging strategy of the marine iguana is an adaptation resulting from the forces of both sexual selection, acting through their unique social system, and natural selection by a harsh and variable environment. We will explore a variety of environmental and physiological constraints (e.g. tidal cycle, the rapid loss of body heat during foraging, variation in body size) that act as overriding selective forces, and are not as salient to their terrestrial counterparts. Finally, we will examine how these constraints have resulted in the adaptation of a variety of unusual morphological characteristics that enable efficient foraging. Thus, we hope to demonstrate how contrasting social and environmental selective pressures on body size have shaped this unique foraging strategy and have resulted in the unusual morphological and behavioral characteristics that first caught Darwin's eye.