Ovaries and oogenesis in an epizoic dermapteran, Hemimerus talpoides (Dermaptera, Hemimeridae): Structural and functional adaptations to viviparity and matrotrophy

The Dermaptera are traditionally classified in three taxa: the free living Forficulina and two viviparous (matrotrophic) groups, the Hemimerina and Arixeniina. Recent molecular and histological analyses suggest that both matrotrophic groups should be nested among the most derived taxon of the Forficulina, the Eudermaptera. We present results of ultrastructural analyses of ovary/ovariole morphology and oogenesis in a representative of the Hemimerina, Hemimerus talpoides (Walker, 1871). Our results strongly reinforce the idea that the Hemimerina should be classified within the Eudermaptera. We show additionally that the ovaries of the studied species are characterized by two peculiar modifications, i.e. the presence of numerous tracheoles in contact with the basement lamina covering the ovarioles, and an unusual development of the ovariole stalks. We believe that both characters are related to viviparity and unconventional “intra-ovariolar” embryo development. Finally, our study also indicates that the oocytes of H. talpoides reveal characters apparently associated with a matrotrophic type of embryo nourishment. They are completely yolkless and devoid of the typical, multilayered egg envelopes; instead, they comprise unconventional organelles (para-crystalline stacks of endoplasmic reticulum cisternae and translucent vacuoles) that seem to function after initiation of embryonic development. Thus, the ovaries as well as the oocytes of H. talpoides are characterized by an exceptional mixture of features shared with derived dermapterans and adaptations to matrotrophy.