Spermatozoa must leave one organism, navigate
long distances, and deliver their paternal DNA into
a mature egg. For successful navigation and delivery,
a sperm-specific calcium channel is activated in the
mammalian flagellum. The genes encoding this
channel (CatSpers) appear first in ancient uniflagellates,
suggesting that sperm use adaptive strategies
developed long ago for single-cell navigation. Here,
using genetics, super-resolution fluorescence microscopy,
and phosphoproteomics, we investigate the
CatSper-dependent mechanisms underlying this
flagellar switch. We find that the CatSper channel is
required for four linear calcium domains that organize
signaling proteins along the flagella. This unique
structure focuses tyrosine phosphorylation in time
and space as sperm acquire the capacity to fertilize.
In heterogeneous sperm populations, we find unique
molecular phenotypes, but only sperm with intact
CatSper domains that organize time-dependent
and spatially specific protein tyrosine phosphorylation
successfully migrate. These findings illuminate
flagellar adaptation, signal transduction cascade
organization, and fertility.