Question

The invasion of an island in Florida by the Cuban brown anole lizard (Anolis sagrei) affected the native anole, A. carolinensis. After A. sagrei invaded, A. carolinensis moved to higher tree perches. Researchers tested whether this change in habitat use caused evolution in the A. carolinensis toepad area; a larger toepad area improves the ability of lizards to grasp the slender branches found high in trees. They measured toepad area of A. carolinensis caught in the wild on islands that were uninvaded and on islands invaded by A. sagrei. They also measured A. carolinensis toepad area in a "common garden experiment" in which A. carolinensis eggs collected on uninvaded and invaded islands were reared to adulthood under identical conditions. Average toepad areas are shown in the table. Wild Caught Uninvaded Invaded Islands Islands 2.08 Common Garden Uninvaded Invaded Islands Islands 2.13 Toepad area (size corrected index) 1. (2 points) Create a bar graph of the results for wild- caught and common garden A. carolinensis. Compare the results for uninvaded versus invaded islands. 2. (3 points) When traits such as toepad area differ consistently between lizards living on uninvaded versus invaded islands, those differences may be due to evolution, phenotypic plasticity or both. Suppose that evolution had been the primary cause of differences in toepad area between lizards from uninvaded versus invaded islands. Under that assumption, predict whether wild-caught results would differ from common garden results. Explain.

Answer 1

1. A simple bar chart using appropriate scales for X and Y axes can be used to visualize the difference between average toepad size in invaded versus uninvaded lands. Wild-caught lizards from invaded islands show a visible increase in the toepad area than their uninvaded counterparts.

2. Evolution acts on variation which may be present in the genes in these lizards. Due to invasion by A. carolinensis, natural selection acted on variants that favored survival in the higher perches in trees, causing certain traits like toepad areas to evolve in the native species. Assuming that evolution is the primary factor at play here, results from wild-caught experiments will not differ significantly from the results from the common-garden experiment. That is because evolution will select for offsprings from individuals that had larger toepads. Eggs from such individuals would have offsprings with larger toepads even in a common garden experiment setting, assuming no plasticity in development is involved.