How is the deep sea like a desert island? It sounds like a child's riddle, but it's actually a serious scientific question with implications for both terrestrial and marine biology. Biologists have long observed that when animals colonize and evolve on isolated islands, small animals tend to become larger while large animals tend to become smaller. Recent research led by MBARI postdoctoral fellow Craig McClain suggests that a similar trend affects animals as they adapt to life in the deep sea. McClain will present a summary of these findings today at the 11th International Deep-Sea Biology Symposium in Southampton, England. A full article is in press in the peer-reviewed Journal of Biogeography.

Biologists ever since Charles Darwin have noted that when animals colonize an isolated island, after millions of years they may evolve into entirely new species that look very different from the original colonizers. For example, a population of mammoths isolated on the Channel Islands of Southern California developed into a new species that weighed only one tenth as much as their relatives on the mainland. Conversely, on some Caribbean islands, tiny shrews evolved into 30-centimeter-long (1-foot-long) "monsters." As these examples illustrate, small animals on islands often grow larger, while large animals become smaller.

Over the last few decades, this general trend (small animals get larger and large animals get smaller) has become known as the "island rule." However, scientists are still debating the rule's applicability and especially its possible causes. For example, animals colonizing an island might struggle to survive in a smaller habitat with limited food, but they might also benefit from fewer predators and less competition for food. All of these factors could influence how an animal's body size evolves over long periods of time.

As a marine biologist, McClain has long been fascinated by deep-sea animals that have evolved into forms
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Contact: Kim Fulton-Bennett
kfb@mbari.org
831-775-1835
Monterey Bay Aquarium Research Institute
10-Jul-2006