Molecular evolution of bumble bee vitellogenin and vitellogenin‐like genes

Abstract

Vitellogenin (Vg), a storage protein, has been significantly studied for its egg yolk precursor role in oviparous animals. Recent studies found that vitellogenin and its Vg‐like homologs were fundamentally involved in many other biological processes in social insects such as female caste differences and oxidative stress resilience. In this study, we conducted the first large‐scale molecular evolutionary analyses of vitellogenin coding genes ( Vg ) and Vg‐like genes of bumble bees, a primitively eusocial insect belonging to the genus Bombus. We obtained sequences for each of the four genes ( Vg , Vg‐like‐A , Vg‐like‐B , and Vg‐like‐C ) from 27 bumble bee genomes (nine were newly sequenced in this study), and sequences from the two closest clades of Bombus , including five Apis species and five Tetragonula species . Our molecular evolutionary analyses show that in bumble bee, the conventional Vg experienced strong positive selection, while the Vg‐like genes showed overall relaxation of purifying selection. In Apis and Tetragonula; however, all four genes were found under purifying selection. Furthermore, the conventional Vg showed signs of strong positive selection in most subgenera in Bombus , apart from the obligate parasitic subgenus Psithyrus which has no caste differentiation. Together, these results indicate that the conventional Vg , a key pleiotropic gene in social insects, is the most rapidly evolving copy, potentially due to its multiple known social functions for both worker and queen castes. This study shows that concerted evolution and purifying selection shaped the evolution of the Vg gene family following their ancient gene duplication and may be the leading forces behind the evolution of new potential protein function enabling functional social pleiotropy.

Evolution and functionalization of vitellogenin genes in the termite Reticulitermes speratus

“…The dN / dS ratios indicated that the branch leading to the common ancestor of termite Vg4 was relatively under weak purifying selection but not in termite Vg1−2 clades (Supporting Information: Figure S2, Table S4). This is not contradicted by the evidence in the bumble bee genus Bombus , which indicated that Vg‐like genes showed a general tendency of relaxation of purifying selection (Zhao et al, 2021). Considering the inferred phylogenetic relationships of insect Vg genes, it is possible that termite Vg4 has diverged less from the outgroups compared to the other termite Vg1−3 genes.…”

Putting hornets on the genomic map

“…Selection pressures associated with social phenotypic plasticity impact the molecular evolution of proteins 83 . We thus explored the rate of protein evolution (dN/dS) for each single-copy orthogroup in the six Vespa and Vespula species (branch models: Supplementary Tables ST8–ST16; branch-site models: Supplementary Tables ST17-ST24).…”

Investigating trade-offs between ovary activation and immune protein expression in bumble bee ( Bombus impatiens ) workers and queens

“…We focused on vitellogenins and immune effectors in our proteomics analysis to examine whether their expression patterns supported the existence of a trade-off. Vitellogenin is an egg yolk protein precursor, but there are four distinct vitellogenin and vitellogenin-like genes in bumble bees [ 42 ] and the proteins are likely multifunctional, as has been shown in other social insects [ 43 ]. Differences in the proteins' domains indicate that they likely have distinct functions, but they have not yet been clearly defined.…”