Spontaneous Intersibling Polymorphism in the Development of Dopaminergic Neuroendocrine Cells in Sea Urchin Larvae: Impacts on the Expansion of Marine Benthic Species

Plasticity of the nervous system enables the formation of the most adaptive neural circuits and the corresponding behavior of animals. The mechanism by which plasticity arises during development and its involvement in animal adaptation is one of the astonishing questions. Sea urchin larvae are known for their evolutionary and ecological diversity as well as their developmental forms and behavioral patterns. This research addresses the intricate neuroendocrine adaptations that govern larval development of sea urchins, focusing on the coordination between dopaminergic (DA) and serotonergic (5-HT) neurons. The study reveals a heterochronic polymorphism in the appearance of post oral DA neurons and confirms the stable differentiation pattern of apical 5-HT neurons in the larvae of Mesocentrotus nudus and Paracentrotus lividus. We demonstrate that an increased number of DA cells and DA application correlate with downward swimming of the larvae. In contrast, 5-HT cells and serotonin application unsure larval upward swimming. As a result, the 5-HT/DA ratio underlay stage-dependent vertical distribution of the larvae within the water column. In larvae of the same age, the precise balance of 5-HT and DA cells underlie the basis for the different potentials of individuals for upward and downward swimming. This coordination in humoral regulation underlies shifts in larval behavior within a single generation. Based on our findings on DA-cells polymorphism, we have proposed a model illustrating how the balance between the serotonin and dopamine systems, shaped by heterochrony in DA cell appearance, impacts larval behavior, reduces competition between siblings and ensures optimal population expansion. The study explores the evolutionary and ecological implications of these neuroendocrine adaptations in marine species. ### Competing Interest Statement The authors have declared no competing interest.