Cichlids are one of the most species-rich families of bony fishes and exhibit an exceptional diversity of color patterns, often rivaling those of coral reef dwellers in their brightness and combination of pattern elements (Fig. 1). The role of endocrine regulatory mechanisms underlying the observed diversity of pigment patterns remains poorly understood. Thyroid hormones are a vital part of the endocrine system and can regulate many growth and development processes, including pigmentation, in vertebrates and humans.
In this study, a researcher at the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (IEE RAS) analyzed the results of long-term experimental studies on the influence of thyroid hormones on the development of pigment patterns in cichlids. Specifically, the study demonstrated the important role of hormones in regulating various types of pigment cells (melanophores, iridophores, xanthophores, and erythrophores) and the formation of adult pattern elements (Fig. 2). The data obtained indicate that thyroid hormones may participate in the evolution of cichlid coloration through various mechanisms.
"Thyroid hormones could be a valuable tool for future research, particularly in assessing the role of variability in the activity of the hypothalamic-pituitary-thyroid axis in the adaptive evolution of various taxonomic groups of fish," said Denis Prazdnikov, PhD, researcher at the Laboratory of Problems of Evolutionary Morphology at the Institute of Ecology and Evolution of the Russian Academy of Sciences.
The article was published published in the journal Hydrobiologia (JCR Q1). Prazdnikov, D.V. (2025), "Thyroid hormone signaling in the evolution of pigment patterns in cichlids: results and research prospects." Hydrobiologia 852 (15), 3819–3830.
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