Question

Insects have three thoracic (trunk) segments. While researchers have found insect fossils with pairs of wings on all three segments, modern insects have wings or related structures on only the second and third segment. It turns out that in modern insects, Hox gene products act to inhibit wing formation on the first segment. The treehopper insect (above) is somewhat of an exception. In addition to having wings on its second segment, the treehopper’s first segment has an ornate helmet that resembles a set of thorns, which a recent study has found to be a modified, fused pair of “wings.” The thorn-like structure helps to camouflage the treehopper in tree branches, thus reducing its risk of predation. Explain how changes in gene regulation could have led to the evolution of such a structure

Short answer

The genes responsible for the wing and helmet formation are related to one another in the treehopper. The coexpression of both genes resulted in myriad elaborate forms in treehoppers by natural selection. The thorn-like structure or helmet originated from the modulation of the ancestral body wall.

Differentially expressed tissue-specific transcriptomes formed a thorn-like structure, which is the most similar to their wings.

Step-by-step solution

Treehopper

Treehoppers are insects that belong to the family Membracidae and order Homoptera. These insects are easily identified by their hood-like covering. They vary in color and secrete honeydew as the byproduct of their digestion.

Treehoppers are known for their mimicry and camouflage by adapting enlarged and ornate pronotum.

Gene regulation in the formation of ornate helmet

Coagulated sets of genes associated with wings and helmet coexpress in the formation of elongated three-dimensional pronotum. The existence of RNA interference supports the versatile development of the outgrowth of the body.

The ancestral body wall patterning network gets extended to form the helmet.

Reason for the formation of ornate helmet in treehoppers

Treehoppers jump from one place to another and do not have much capacity to fly. They have developed an ornate helmet that aids in predation defense. Natural selection acts as an evolutionary force here, and the desire to survive brought the necessary changes in the organism.

In treehoppers, the regulatory genes responsible for wing formation are upregulated, and the wing co-option scenario caused the origin of the helmet.