Independent Evolution of Linear and Branched Cuticular Hydrocarbons in Ants: A Hypothesis

The epicuticle of Cataglyphis niger is endowed with hydrocarbons comprising both linear and branched alkanes. For linear alkane, it is hypothesized that the primary driving force for their evolution was acquiring means for attaining cuticular impermeability that protects the ants from desiccation, and, secondarily, was co-opted as cues and signals. For example, being more abundant in foragers, they signal colony foraging intensity and, accordingly, adjust task allocation. Branched alkanes serve mostly in communication, but their evolution is less clear. Studies of the biosynthesis of both classes of hydrocarbons revealed disparate pathways, which suggests an independent evolution. The biosynthesis of branched alkanes hints at their possible evolution. They are derived from branched fatty acids, which have evolved as protective means due to their bactericidal activity. It is hypothesized that their biosynthetic pathway was secondarily co-opted for producing branched alkanes as signals and cues. Branched alkanes blend within the linear alkane layer to evenly cover the ants' body surface and enhance the ants' communicative capacity by conveying larger informational content due to their numerous positional and stereoisomers. The present study presents the occurrence of substantial amounts of branched fatty acids with branching position that matches that of the branched alkanes. The disparate biosynthesis pathways and the postulated differences in their evolutionary roots lend credence to the hypothesis of their independent evolution.