(photograph = Opuntia cyclodes spines)
Introduction
Opuntia cyclodes has yellow spines. This feature is constant over the entire range of the species. O. cyclodes is present off and on over about 40,000 square miles of NM and TX, and the spine color is the same everywhere. Why would a species have such strict rules enforcing spine color? Spines of other Opuntia species can vary from yellow, to white, to brown, or even may be bicolored.
The Details
Natural Selection tells us that having such strict rules is not an accident. Natural Selection tells us that something is keeping the species from having other spine colors. There is enforcement. However, why yellow?
It is really impossible to know “why yellow” without experimentation. However, some hypotheses can be advanced.
- Perhaps yellow spines reflect or filter light a certain way and this might attract certain pollinators that help the plant reproduce.
- It is possible that certain herbivores recognize the yellow spines and avoid eating the plant.
- Perhaps the yellow pigment(s) are attractive to ants that colonize the plant and prevent other insects from colonizing.
It is easy to dream up ideas about what we see in Nature and why we see it. But, it is difficult to demonstrate that the ideas are correct. In this way, Nature is like politics; ideas abound but facts are scarce.
Additional Reading: Natural Selection
