Morphology of the nervous system of monogonont rotiferEpiphanes sentawith focus on sexual dimorphism between feeding females and dwarfed males

Background Monogononta is a large clade of rotifers comprised of diverse morphological forms found in a wide range of ecological habitats. Most of the monogonont species display a cyclical parthenogenesis, where generations of asexually reproducing females are interspaced by mixis events when sexual reproduction occurs between mictic females and dwarfed, haploid males. The morphology of monogonont feeding females is relatively well described, however data on male anatomy are very limited. Thus far, male musculature of only two species has been described with confocal laser scanning microscopy (CLSM) and it remained unknown how dwarfism influences neuroanatomy of males. Results Here, we provide a CLSM-based description of the nervous system of both sexes of Epiphanes senta , a freshwater monogonont rotifer. The general nervous system architecture is similar between males and females and shows same level of complexity. However, the nervous system in males is more compact and lacks its stomatogastric part. Conclusion Comparison of the neuroanatomy between male and normal-sized feeding females provides better understanding of the nature of male dwarfism in Monogononta. We propose that dwarfism of monogonont non-feeding males is a specific case of progenesis as they, due to their inability to feed, retain a juvenile body size. Reduction of the stomatogastric nervous system in the males correlates with the loss of entire digestive tract and associated morphological structures.