Meeting Abstract
Paedomorphosis is often suggested to be the evolutionary pathway leading to the origin of interstitial meiofauna. The environmental demands of the interstices supposedly warrant a one-step miniaturization from macroscopic to microscopic animals. Serial paedomorphic events may lead to more reduced descendants within interstitial groups. Here, we examine this phenomenon within the genus Dinophilus (Dinophilidae) – having two morphotypes as well as dwarf males. While monomorphic D. taeniatus has a very long life cycle including encystment, the dimorphic D. gyrociliatus has a life cycle of less than one month. The onset of muscular, nervous and ciliary development is very similar between these two species. The main differentiation occurs short before hatching, when D. taeniatus adds longitudinal and transverse muscles to the early layout, while D. gyrociliatus females do not. More peculiar is the nervous system, forming first one thick neurite bundle per segment linking the two prominent longitudinal strands, and afterwards splitting into three thinner ones. While D. gyrociliatus seems to retain this layout in the adult stage, D. taeniatus later in development again fuses the three commissures to one per segment. The additional ciliary band per segment in D. taeniatus forms short before or even after hatching. Although there is no molecular data on how these two species are related, we have some evidence, that their common ancestor probably resembled D. taeniatus. This would mean that the neuro-muscular architecture of D. gyrociliatus is paedomorphic. However, a molecular phylogeny of the genus Dinophilus is needed to clarify and support this hypothesis.
