  We consider a two-dimensional Fermi liquid coupled to low-energy commensurate
spin fluctuations. At small coupling, the hole Fermi surface is large and
centered around $Q =(\pi,\pi)$. We show that as the coupling increases, the
shape of the quasiparticle Fermi surface and the spin-fermion vertex undergo a
substantial evolution. At strong couplings, $g \gg \omega_0$, where $\omega_0$
is the upper cutoff in the spin susceptibility, the hole Fermi surface consists
of small pockets centered at $(\pm \pi/2, \pm \pi/2)$. Simultaneously, the full
spin-fermion vertex is much smaller than the bare one, and scales nearly
linearly with $|q-Q|$, where $q$ is the momentum of the susceptibility. At
intermediate couplings, there exist both, a large hole Fermi surface centered
at $(\pi,\pi)$, and four hole pockets, but the quasiparticle residue is small
everywhere except for the pieces of the pockets which face the origin of the
Brillouin zone. The relevance of these results for recent photoemission
experiments in $YBCO$ and $Bi2212$ systems is discussed.
