  Community structures in collaboration networks reflect the natural tendency
of individuals to organize their work in groups in order to better achieve
common goals. In most of the cases, individuals exploit their connections to
introduce themselves to new areas of interests, giving rise to multifaceted
collaborations which span different fields. In this paper, we analyse
collaborations in science and among movie actors as multiplex networks, where
the layers represent respectively research topics and movie genres, and we show
that communities indeed coexist and overlap at the different layers of such
systems. We then propose a model to grow multiplex networks based on two
mechanisms of intra and inter-layer triadic closure which mimic the real
processes by which collaborations evolve. We show that our model is able to
explain the multiplex community structure observed empirically, and we infer
the strength of the two underlying social mechanisms from real-world systems.
Being also able to correctly reproduce the values of intra-layer and
inter-layer assortativity correlations, the model contributes to a better
understanding of the principles driving the evolution of social networks.
