Duplication of the anteroposterior body axis in postembryos of theEratigena atricaspider

ABSTRACT Many factors, including temperature, can affect the embryonic development of spiders, leading to a variety of deformities in their body structure. Early studies on teratological changes in spiders were aimed mainly at describing the morphology of affected individuals. Now, with new tools and molecular techniques used to carry out a functional analysis of genes involved in body segmentation and leg formation, the explanation of these defects is finally possible. In our new experiment on spiders collected in 2022/2023 breeding season, we obtained 87 postembryos with various body defects by applying alternating temperatures (14 0 C and 32 0 C) for the first 10 days of embryonic development. The most common anomaly, i.e. oligomely, occurred in 70 individuals, while other defects (schistomely, symely, polymely, heterosymely) were noted sporadically. Partial prosoma duplication affected only six embryos. In the context of recent advances in molecular spider embryology we conclude that recorded anomalies may be connected with the suppression or erroneous expression of certain genes of body segmentation and appendage formation, and by disturbances in the formation and migration of the cumulus, which leads to an axis duplication phenotype. Summary statement This article presents a rare anomaly - bicephaly, which appeared in spider postembryos as a result of thermal shocks applied during embryogenesis.