Many aspects of the evolutionary history of these lizards are consistent with the theory that morphs can be involved in speciation, Corl said. Evolutionary theory predicts that new species could arise from particular morphs originally found in a population containing multiple morphs. Side-blotched lizards started off with three color morphs. If just one or two types occur in a population, they look just like the original morphs.
The theory was also supported by patterns in the formation of subspecies, which are the precursors to new species. Two subspecies of side-blotched lizard that originated from populations with three morphs now have only a single color morph. Thus, populations that lose morphs are not transitory, but can persist and eventually become a different species.
The study also found evidence to support the hypothesis that rapid evolutionary change occurs when particular morphs are lost from the system. "Imagine the three lizard morphs playing rock-paper-scissors," Corl explained. "They have very specific adaptations for fighting one another. Now imagine that some morphs are lost, leaving a population of all rock morphs. Their adaptations for fighting the paper and scissors morphs are no longer useful. Therefore, rapid evolutionary change is expected in a population of rock morphs as they adapt to a new game in which they only fight other rock morphs."
The study showed clear evidence of very rapid evolution of body size when morphs are lost from a population. "Such rapid evolution could eventually cause populations to evolve into distinct species. We are the first group to provide a statistical test of this hypothesis," Corl said.
The idea of morphs being involved in speciation is an old one. Charles Darwin condu
|Contact: Tim Stephens|
University of California - Santa Cruz