Figure 2

Summary of tubulin isoform relationships. Each of the β1, β2, β3, and β4 isoforms is represented in both hemimetabolous and holometabolous insect taxa, indicating they evolved prior to the separation of these taxa. The β2 isoform duplicated in holometabolous insects following their separation from hemimetabolous insects, based on the clade containing Amβ2b, Nvβ2b, Nvβ2c, Tcβ2b. The β2b isoform was lost in the Lepidoptera/Diptera ancestor, and the β2c isoform was lost in every holometabolous taxa except Nv. The β4 isoform is represented in hemimetabolous insects and Diptera, indicating independent losses in Hymenoptera, Coleoptera, and Lepidoptera. Each of the α1, α2, and α4 isoforms are represented in both hemimetabolous and holometabolous insect taxa, indicating they evolved prior to the separation of these taxa. The α3 isoforms, present in Tc and Bm, fall within the α1 isoforms, suggesting its origin in a duplication event in the common ancestor of Coleoptera, Lepidoptera, and Diptera that was lost in Dipterans.