The cutting edge of the lock-and-key hypothesis in weevils: a case study of Sitona fairmairei (Coleoptera, Curculionidae)

According to a perspective, male and female copulatory organs have not more extreme morphologies. However, a skewed bias in males, -as well as the scanty taxonomic data on female genitalia, may explain why most evolutionary biologists failed to find acceptable evidence for the reproductive co-evolution in insects. A recent finding shows that the mechanical footing has a cooperative essence in the weevil genus Sitona. In this viewpoint, successful mating is achieved by the dynamic correspondence between the male endophallus and female genital lumen. The present work addresses some missing evidence in the genital traits of this taxon that may keep the hampered comprehensions under lock and key. The female bursal lumen in the studied species is provisioned with a pair of forklift-shaped structures (named the “codelocks”) that may provide for stabilizing the characteristic position of the male bio-syringe during copulation. This structure varies between the species based on the shape and direction of its paired levers, so that an elaborate algorithm possibly serves as the fuel of this device. However, in one of these, Sitona fairmairei (Allard, 1869), the levers perform a dual function in accordance to the lockback mechanism of the male copulatory organ. This species is also featured for having several campaniform mechano-receptors on the flanges of the male bio-syringe which are involved in the in-vivo navigation of this armature towards female spermathecal duct.