Ubxpromotes corbicular development inApis mellifera

Abstract

The key morphological feature that distinguishes corbiculate bees from other members of the Apidae family is the presence of the corbicula (pollen basket) on the tibial segment of hind legs. Here, we show that in the honeybee (Apis mellifera), the depletion of the gene Ultrabithorax (Ubx) by RNAi transforms the corbicula from a smooth, bristle-free concave structure to one covered with bristles. This is accompanied by a reduction of the pollen press, which is located on the basitarsus and used for packing the pollen pellet as well as a loss of the orderly arrangement of the rows of bristles that form the pollen comb. All these changes make the overall identity of workers' T3 legs assume that of the queen. Furthermore, in a corbiculate bee of a different genus, Bombus impatiens, Ubx expression is also localized in T3 tibia and basitarsus. These observations suggest that the evolution of the pollen gathering apparatus in corbiculate bees may have a shared origin and could be traced to the acquisition of novel functions by Ubx, which in Apis were instrumental for subsequent castes and behavioural differentiation.

The ontogenetic saga of a social brain

“…Bomtorin et al (2012) showed that the development of the Bshaved tibia^used by workers to carry pollen (pollen basket) depends upon ultrabithorax expression during prepupal and early pupal phases. This finding was then confirmed by Medved et al (2014) using gene expression interference by RNAi.…”

A homeotic shift late in development drives mimetic color variation in a bumble bee

“…Shifts in Scr expression influence male sex comb morphology in Drosophila forelimbs (67) and the formation of crustacean maxillipeds (68). Similarly, regional upregulation of Ubx along insect hindlimbs drives growth and setal loss (69,70), such as that observed in the expanded corbicula pollen basket in honey bees and bumble bees (71). Such variation during late development could be driven by Hox genes evolving to respond to downstream components of regulatory networks, further enabling developmental micromanagement (57,67).…”

Hexapoda: Comparative Aspects of Later Embryogenesis and Metamorphosis

“…This is a rare example in which the genomic locus of phenotypic evolution has been identifi ed. In honeybees, workers and queens differ in leg bristle patterns, which are controlled by differences in the timing and expression levels of Ubx (Bomtorin et al 2012 ;Medved et al 2014 ). These caste differences are phenotypically plastic, but it is not yet known how the environmental signal is translated into a difference in Ubx expression.…”