Morphological colour adaptation during development: Involvement of Growth Hormone Receptor 1

Morphological background adaptation is both an endocrine and a nervous response, involving changes in the amount and shape of chromatophores. However, if this adaptation takes place at early developmental stages is largely unknown. Somatolactin (SL) is a pituitary hormone present in fish, which has been associated to skin pigmentation. Moreover, growth hormone receptor type 1 (ghr1) has been suggested to be the SL receptor and was associated to background adaptation in adults. In this context, the aim of this work was to evaluate the ontogeny of morphological adaptation to background and the participation of ghr1 in this process. We found in larval stages of Cichlasoma dimerus that the number of head melanophores and ir-SL pituitary cells were increased in individuals reared in black backgrounds compared to fish grown in white tanks. In medaka (Oryzias latipes) larval stages a similar response was observed that is altered by a ghr1 biallelic mutations using CRISPR/cas9. Interestingly, melanophore and leucophore numbers are highly associated. Furthermore, we found that somatic growth is reduced in ghr1 biallelic mutant medaka, establishing the dual function of this growth hormone receptor. Taken together, these results show that morphological background adaptation is present at early stages during development and that is dependent upon ghr1 unless during this period.