Neurobiology of Reproduction in Mollusks: Mechanisms and Evolution

Ultimately, the outcome of successful reproduction—fertilization of eggs and production of surviving offspring—is relevant for how these processes evolve. However, a thorough understanding of the underlying, proximate mechanism is essential for interpreting evolutionary outcomes properly. Comparing neuroendocrine processes across different species, with different sexual systems, is one way of uncovering similarities and differences in regulation of their reproductive processes. Here, we provide an overview of the neuroendocrine control of reproductive processes in mollusks. In doing so, we also illustrate that it is relevant to consider the sexual system when addressing the neurobiology of reproduction. For example, our overview indicates that hermaphroditic mollusks seem to regulate their male and female reproduction via largely nonoverlapping neurobiological wiring and neuroendocrine substances, whereas this is not necessarily the case for separate-sexed mollusks. Clearly, this has implications for the available degrees of freedom within sexual systems in terms of evolutionary pathways.