  We show the existence of two new Shimura subvarieties of $\mathcal{A}_2,
\mathcal{A}_3$ generically contained in the Torelli locus. They provide the
first examples of Shimura subvarieties obtained by means of Jacobians carrying
non-trivial endomorphisms not directly induced by the automorphisms of the
curves. We also obtain a new example of a Shimura subvariety of $\mathcal{A}_4$
generically contained in the Prym locus.
