  Sperm cells perform extremely demanding tasks with minimal capabilities. The
cells must quickly navigate in a noisy environment to find an egg within a
short time window for successful fertilization without any global positioning
information. Many research efforts have been dedicated to deriving mathematical
principles that explain their superb navigation strategy. Here we show that the
navigation strategy of sea urchin sperm, also known as helical klinotaxis, is a
natural implementation of a well-established adaptive control paradigm known as
extremum seeking. This bridge between control theory and the biology of taxis
in microorganisms is expected to deepen our understanding of the process. For
example, the formulation leads to a coarse-grained model of the signaling
pathway that offers new insights on the peculiar switching-like behavior
between high and low gain steering modes observed in sea urchin sperm.
Moreover, it may guide engineers in developing bio-inspired miniaturized robots
with minimal sensors.
