Letter: Spittlebug morph mimics avian excrement

Principles underlying chromatophore addition during maturation in the European cuttlefish, Sepia officinalis

The goal of this work was to identify some of the principles underlying chromatophore growth and development in the European cuttlefish, Sepia officinalis. One set of experiments used a regeneration model to follow the re-growth of black chromatophores for 30 days following excision of a small piece of fin tissue. A separate set of experiments tracked and analyzed the addition of new fin chromatophores during a month of normal, undisturbed growth. We also followed the development of individual chromatophores from their initial appearance to full maturation to determine whether their color type was fixed. Based on the results of these studies, we propose five guiding principles for chromatophore growth and maturation. (1) The three chromatophore cell types--black, reddish-brown and yellow--are present at different spatial frequencies in the cuttlefish fin. (2) During normal growth, new chromatophores are inserted at a higher spatial frequency than existing (control) chromatophores of the same color type. (3) In regenerating tissue, new black chromatophores are initially added at low spatial frequencies. As regeneration continues, new black chromatophores appear at increasing spatial frequencies until they are inserted at a spatial frequency higher than that observed in control tissue, similar to the way in which chromatophores were observed to be added in normally growing tissue. (4) All chromatophores first appear as pale orange cells and slowly darken into their respective color types without passing through intermediate color stages. (5) New black chromatophores undergo a doubling in size as they mature, while reddish-brown and yellow chromatophores do not grow at all after they are inserted in the dermis.