Complex Systems Approach to Sea Urchin Sperm Navigation
M. Aldana [1], J. Espinal [1], G. Martinez [1], A. Darszon [2], A. Guerrero [2], C. Wood [2]

[1] Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Cuernavaca, Morelos, [2] Instituto de Biotecnologia, Universidad Nacional Atuonoma de Mexico, Cuernavaca Mexico

Abstract: Fertilization is one of the fundamental processes of living systems. Here we study how sea urchin sperms swim towards the egg. As is usual in complex systems, several levels of description are involved in this process. In this presentation we focus, at the biochemical level, on how polypeptides secreted by the egg trigger signaling pathways for calcium oscillations in the flagellum, which modify sperm navigation, producing on occasions chemotaxis. Our theoretical analysis is based on experimental determinations performed within our group. Our modeling incorporates discrete and semi-continuous dynamical formalisms developed for the study of complex networks. Several experimental observations are recovered and some predictions have been corroborated by new experiments. The finding that the chemical network operates at criticality, as in critical phenomena, is a matter for future reflection. Finally, as an overview, we comment on some aspects of sperm navigation related to other levels of description, such as molecular machines present in the flagellum, hydrodynamic considerations and space exploration strategies. A proper understanding and integration of these levels of description is an open challenge.