Meeting Abstract
The question of whether ctenophore neurons have evolved independently has caused widespread uncertainty about the origin of nervous systems in animals. Arguments for the independent origins of animal nervous systems have centered on the absence of conserved “neural” genes and neurotransmitters in ctenophores. Here we reconsider this question by examining the developmental origin of neurons across animals. We present examples from the literature of neural cell types deriving from cell lineages that exclusively give rise to non-neural cell types in other animals. We further show that neural progenitor cells also give rise to non-neural secretory cells in numerous animal taxa. Together, these patterns reflect the labile nature of cell identity and underscore the futility of arguing for the homology of neural cell types. Rather, we advocate for the concept of a single origin of a generic secretory cell in the stem of all animals to better understand the early evolution of neurons and the potential loss of neural cell types in sponges and placozoans. Lastly, we present unpublished electrophysiology data suggesting that ctenophore neural cell types have similar electrical properties to those of cnidarians and bilaterians. Together, these ideas offer a new perspective from which to evaluate current data and outline specific experiments that could newly illuminate the evolution of neural cell types; this in turn will lead to a better understanding of animal nervous systems, including our own.
