  The ratio of bulk to shear viscosity is expected to exhibit a different
behaviour in weakly and in strongly coupled systems. This can be expressed by
its dependence on the squared sound velocity. In the high temperature QCD
plasma at small running coupling, the viscosity ratio is uniquely determined by
a quadratic dependence on the conformality measure, whereas in certain strongly
coupled and nearly conformal theories this dependence is linear. Employing an
effective kinetic theory of quasiparticle excitations with medium-modified
dispersion relation, we analyze the ratio of bulk to shear viscosity of the
gluon plasma. We show that in this approach, depending on the temperature, the
viscosity ratio exhibits either of these dependencies found by means of weak
coupling perturbative or strong coupling holographic techniques. The turning
point between the two different dependencies is located around the maximum in
the scaled interaction measure.
