  In this letter we show that the dispersion relation for the dynamical modes
of dislocations in solids is sensitive to the lattice symmetries. In
particular, we make the sharp prediction that the transverse oscillations of
dislocations obey a canonical phononic linear dispersion relation (so-called
type I Goldstone bosons) for generic lattices. However, for systems with a
discrete cubic symmetry, the modes obey a quadratic dispersion relation (type
II Goldstone bosons). This difference will show up in various observables,
including the phonon lifetime. We show that the ratio of the phonon lifetimes,
at leading order in the low energy expansion, scales as $\tau_{I}/\tau_{II}
\sim (dE_{II}/dk)/(dE_I/dk)= k/(m v) $ where v is the type I Goldstone velocity
and m the mass parameter which appears in the type II dispersion relation.
