  Inertialess anisotropic particles in a Rayleigh-B\'enard turbulent flow show
maximal tumbling rates for weakly oblate shapes, in contrast with the universal
behaviour observed in developed turbulence where the mean tumbling rate
monotonically decreases with the particle aspect ratio. This is due to the
concurrent effect of turbulent fluctuations and of a mean shear flow whose
intensity, we show, is determined by the kinetic boundary layers. In
Rayleigh-B\'enard turbulence prolate particles align preferentially with the
fluid velocity, while oblate ones orient with the temperature gradient. This
analysis elucidates the link between particle angular dynamics and small-scale
properties of convective turbulence and has implications for the wider class of
sheared turbulent flows.
