Somatic anomalies in Formicidae: new cases and discussion of anomaly origin during immature development

Originally viewed as monstrosities or scientific curiosities, developmental anomalies have been widely reported in arthropods since the nineteenth century. However, it was only after Wheeler's studies on ants and Balazuc's investigations on numerous other arthropods that anomalous individuals began to be systematically analyzed. Denominations for these individuals have varied greatly, generating a confusing or often contradictory nomenclature. In Hymenoptera, sexual dimorphism arises from a haplodiploid sex-determination system. During embryonic and post-embryonic development, defects can result in the formation of abnormal individuals carrying morphological or genetic aberrations that can be classified according to criteria based on body location. Gynandromorphs or sex mosaics are individuals that simultaneously display male and female characters, either bilaterally or in mosaics. Other somatic abnormalities may be a consequence of defects and injuries that occurred during embryonic or post-embryonic development. Using literature data on 85 species of ants distributed in 8 subfamilies and detailed descriptions of a series of collection individuals, we reviewed the current definitions of somatic developmental anomalies and proposed a simplified classification based on currently available nomenclature. In addition to presenting a causality discussion, we arranged the cases of gynandromorphs, mosaics, and teratological forms in a sequence and hypothesized about the temporal origin of alterations. The large majority of cases reported in the literature are of gynandromorphism, followed by teratology. Analysis of such phenomena raises behavioral, genetic, and ecological questions related to the viability of anomalous individuals.