  We investigate the temperature ($T$)-evolution of orbital anisotropy and its
effect on spectral function and optical conductivity in Ce$_{2}$IrIn$_{8}$,
using a first principles dynamical mean field theory combined with density
functional theory. The orbital anisotropy develops by lowering $T$ and it is
intensified below a temperature corresponding to the crystalline-electric field
(CEF) splitting size. Interestingly, the depopulation of CEF excited states
leaves a spectroscopic signature, "shoulder", in the $T$-dependent spectral
function at the Fermi level. From the two-orbital Anderson impurity model, we
demonstrate that CEF splitting size is the key ingredient influencing the
emergence and the position of the "shoulder". Besides the two conventional
temperature scales $T_{K}$ and $T^{*}$, we introduce an additional temperature
scale to deal with the orbital anisotropy in heavy fermion systems.
