Evading a hungry predator is essential if your genes are to contribute to the game of life and speed is usually of the essence. However, it's not always that simple. Animals often drop their speed in favour of agility as they try to outmanoeuvre pursuers. And what happens if you take the pursuit into the trees, where prey have to negotiate branches of different girth? Wondering how green anole lizards adapt their flight in different contexts, Erik Sathe and Jerry Husak from the University of St Thomas, USA, began investigating how animals of different builds sprinted along branches of different widths, along the flat and through a maze of peg obstacles to find out which physical attributes prepared the lizards best for escape.
Sure enough, the sprinting animals were fastest on a flat surface and the broadest pole (5 cm), reaching speeds of over 1.4 m s−1, but they dropped to 0.8 m s−1 on the 2.5 cm pole and were reduced to a crawl (0.4 m s−1) through the maze of pegs. Next, they investigated which physical characteristics gave the lizards an edge in each of the different settings and found that lizards with short toes and large forelimbs performed the fastest on the flat. Meanwhile, small forelimbs gave the lizards a speed advantage on the 5 cm pole. However, lizards weaving through the peg obstacle course performed faster when the muscle that pulls the forelimb back was large; and long toes and small limbs produced nimble animals that negotiated the peg obstacles best.
Overall, Sathe and Husak found that animals that performed well in one context tended to perform poorly in others, suggesting that an animal's optimal performance is not fixed and may vary depending on the environment. They also suggest, ‘Natural selection may act on an individual's ability to cope with substrate variation’, adding that instead of optimising their performance in one setting, animals that live in complex environments may settle on the least worse compromise, making green anoles Jacks of all trades and masters of none in their complex tree homes.