Comparative morphology and function of Chloropidae (Diptera) tibial organ

The tibial organ of Chloropidae and Milichiidae flies is an obscure feature with taxonomic significance. This study provides the first in-depth investigation into the ultrastructure of the hind leg of 11 genera from all Chloropidae subfamilies using a multimodal microscopy approach. The modified dermal tissue associated with the tibial organ indicates glandular function, as evidenced by the presence of secretory vesicles containing non-proteinaceous elements, potentially indicating lipidic secretion. The overall similarity of the tibial organ between Chloropidae and Milichiidae indicates a shared homology. However, the evolutionary history of this structure is still contentious due to limitations in the phylogenetic relationships of both lineages. Moreover, our findings enable future comparative investigations of other Diptera leg organs that possess secretory ability, which could be homologous across schizophoran families, but not necessarily the organs themselves.