  In this paper we compute the pullback of divisor classes under the Prym map
(extended to the boundary), and apply this result to get a lower bound on the
slope of effective divisors on the perfect cone compactification of the moduli
space of principally polarized abelian fivefolds.
  In the appendix by Klaus Hulek, the notion of slope for arbitrary toroidal
compactifications is discussed, and the slope bound is shown to hold in
general.
