Meeting Abstract
The evolutionary origin of the insect head has been of longstanding interest in evolutionary biology. Much is known about the formation of the ventral head containing the mouthparts, yet dorsal head formation remains poorly understood, in particular during the transformation of larval to pupal/adult stages. This is particularly problematic as many insect groups have evolved diverse dorsal adult head morphologies as well as integrated novel and ecologically important structures such as shields, stalks, or horns, into dorsal adult head formation. We investigate the developmental origin of the adult dorsal head from larval precursor tissues, evaluate the evolutionary conservation of that process, and investigate the mechanisms underlying the integration of novel head structures – horns – within the context of head formation. Specifically, we use selective ablation of regions of the larval head epidermis to map the fate of this tissue during pupation in three species of horned Onthophagus beetles exhibiting species-specific differences in horn location and number. Here we present the first larval-to-adult fate map for the dorsal adult head of any holometabolous insect. We then show that while most components of this fate map are conserved across diverse Onthophagus species in terms of location, the exact phenotypic response to regional ablation vary as a function of species and sex, indicating species-specific differences in the developmental potential of homologous head regions. Lastly, we provide evidence suggesting that posterior head horns have become integrated into head formation by re-using the same positioning mechanism that generates head segment boundaries in embryos and larvae, while anterior head horns may have evolved their positioning mechanisms de novo, possibly explaining their relative rarity.
