Thyroid hormone signaling in the evolution of pigment patterns in cichlids: results and research prospects

Cichlids exhibit an outstanding diversity of pigment patterns among both teleosts and vertebrates in general. The role of endocrine regulatory mechanisms underlying the observed diversity of patterns remains poorly understood. Thyroid hormones are important signaling molecules that regulate a wide range of developmental processes in teleosts. Here, I review evidence for the influence of thyroid signaling on pigment pattern formation in Neotropical cichlids, and the role of hormone-mediated phenotypic plasticity and heterochrony in the evolution of cichlid pattern. The use of hormones as key factors in switching developmental programs in future studies will provide a better understanding of how environmentally-mediated changes in the endocrine regulation of ontogeny contribute to adaptive evolution and the phenotypic divergence of cichlids.