  Recent imaging of protoplanetary disks with high resolution and contrast have
revealed a striking variety of substructure. Of particular interest are cases
where near-infrared scattered light images show evidence for low-intensity
annular "gaps." The origins of such structures are still uncertain, but the
interaction of the gas disk with planets is a common interpretation. We study
the impact that the evolution of the solid material can have on the observable
properties of disks in a simple scenario without any gravitational or
hydrodynamical disturbances to the gas disk structure. Even with a smooth and
continuous gas density profile, we find that the scattered light emission
produced by small dust grains can exhibit ring-like depressions similar to
those presented in recent observations. The physical mechanisms responsible for
these features rely on the inefficient fragmentation of dust particles. The
occurrence and position of the proposed "gap" features depend most strongly on
the dust-to-gas ratio, the fragmentation threshold velocity, the strength of
the turbulence, and the age of the disk, and should be generic (at some radius)
for typically adopted disk parameters. The same physical processes can affect
the thermal emission at optically thin wavelengths ($\sim$1 mm), although the
behavior can be more complex; unlike for disk-planet interactions, a "gap"
should not be present at these longer wavelengths.
