  We explore a chameleon type of interacting dark matter-dark energy scenario
in which a scalar field adiabatically traces the minimum of an effective
potential sourced by the dark matter density. We discuss extensively the effect
of this coupling on cosmological observables, especially the parameter
degeneracies expected to arise between the model parameters and other
cosmological parameters, and then test the model against observations of the
cosmic microwave background (CMB) anisotropies and other cosmological probes.
We find that the chameleon parameters $\alpha$ and $\beta$, which determine
respectively the slope of the scalar field potential and the dark matter-dark
energy coupling strength, can be constrained to $\alpha < 0.17$ and $\beta <
0.19$ using CMB data alone. The latter parameter in particular is constrained
only by the late Integrated Sachs-Wolfe effect. Adding measurements of the
local Hubble expansion rate $H_0$ tightens the bound on $\alpha$ by a factor of
two, although this apparent improvement is arguably an artefact of the tension
between the local measurement and the $H_0$ value inferred from Planck data in
the minimal $\Lambda$CDM model. The same argument also precludes chameleon
models from mimicking a dark radiation component, despite a passing similarity
between the two scenarios in that they both delay the epoch of matter-radiation
equality. Based on the derived parameter constraints, we discuss possible
signatures of the model for ongoing and future large-scale structure surveys.

Cosmology and Nongalactic Astrophysics;General Relativity and Quantum Cosmology