Types Of Chromatophores Research Articles

Adaptation of the tree frog, Hyla cinerea, to colored backgrounds, and the rôle of the three chromatophore types

AbstractMeasurements have been made of the spectral reflectance of the dorsal skin of living tree frogs, Hyla cinerea.The colors assumed by the frogs when placed on backgounds of different col‐ors varied with respect to both dominant wavelength (565–580 nm), purity (42–58%) and lightness (2–19%).A certain adaptation to the lightness of the background took place, whereas adaptation to hue and purity seems almost negligible.On the basis of reflection measurements of single chromatophores and chro‐matophore associationa, a model is proposed for the color generation in the chromatophores, assuming an absorption of short‐wave light in the xantho‐phores, a reflection of short‐and medium‐wave light (blue, green) from the iridophores, and almost total absorption of all light in the melanophores, and a uniform, but subtotal, reflection of light of all wavelenghts from the connective tissue.It is suggested that the states of dispersion of the three types of chro‐matophores may be related to simple parameters which can be calculated from the reflectance spectra. Using these parameters it was found that mela‐nophores, xanthophores and iridophores all play an active part in the color change, and an explanation is presented on how the observed frog colors are generated by means of changes in the chromatophores.The three types of chromatophores probably are able to react independently of each other, thus indicating that the unihumoral theory fails to explain the color changes in Hyla cinerea.

Light-induced electron transport pathways in membrane preparations from Rhodopseudomonas capsulata

The photosynthetic electron transport chain in Rhodopseudomonas capsulata cells was investigated by studying light-induced noncyclic electron transport from external donors to O 2. Two membrane preparations with opposite membrane polarity, heavy chromatophores and regular chromatophores, were used to characterize this electron transport. It was shown that with lipophylic electron donors such as dichloroindophenol, diaminobenzidine, and phenazine methosulfate the electron transport activities were similar in both types of chromatophores, whereas horse heart cytochrome c, K 4Fe(CN) 6, 3-sulfonic acid phenazine methosulfate, and ascorbate, which cannot penetrate the membrane, were more active in the heavy chromatophores than in the regular chromatophores. Partial depletion of cytochrome c 2 from the heavy chromatophores caused a decrease in the light-induced O 2 uptake from reduced dichloroindophenol or ascorbate. The activity could be restored with higher concentrations of dichloroindophenol or with purified cytochrome c 2 from Rps. capsulata. It is assumed that in the heavy chromatophores the artificial electron donors are oxidized on the cytochrome c 2 level which faces the outside medium. However, cytochrome c 2 is not exposed to the outside medium in the regular chromatophores. Therefore, only lipophylic donors would interact with cytochrome c 2 in this system, while hydrophylic donors would be oxidized by another component of the electron transport chain which is exposed to the external medium. Studies with inhibitors of photophosphorylation show that antimycin A enhances the light-dependent electron transport to O 2 whereas 1:10 phenanthroline inhibited the reaction, but dibromothymoquinone did not affect it. It is assumed that a nonheme iron protein is taking part in this electron transport but not a dibromothymoquinone-sensitive quinone. The terminal oxidase of the light-dependent pathway is different from the two oxidases of the respiratory chain. The ratio between electrons entering the system and molecules of O 2 consumed is 4, which means that the end product of O 2 reduction is H 2O.

Electron microscopy of two types of reflecting chromatophores (iridophores and leucophores) in the guppy, Lebistes reticulatus Peters.

Reflecting chromatophores in the integument of the guppy, Lebistes reticulatus Peters, are of two distinct types, iridophores and leucophores. The iridophores are smaller and fixed, producing a metallic iridescent color. The cytoplasmic organelles involved in the coloration of iridophores are the reflecting platelets, as in the iridophores of other fish and amphibian species on which earlier reports have been made. Spherical granules of pleiomorphic internal structure, quite variable in size but generally 0.2 mum to 1.0 mum in diameter, are also numerous in the iridophores. The nature of these granules remains unknown. The leucophores are larger, and highly dendritic; their pigment granules are migratory and they exhibit a dull whitish color. Pigment granules of the leucophores are spherical in form, varying from 0.5-0.8 mum in diameter, with a double membrane enclosing the internal fibrous materials. Melamine-treatment of the fish caused degenerative changes in the pigment granules and also the other cytoplasmic organelles of the leucophores, whereas the other kinds of chromatophores, including the iridiophores, remained intact. Some problems in general characterization and classification between these two types of chromatophores were discussed.

The Location and Function of Cytochrome c2 in Rhodopseudomonas capsulata Membranes

Two fractions of membrane preparations, a heavy and a light one were isolated from mildly broken Rhodopseudomonas capsulata cells. The light fraction which contained vesicles similar to the regular chromatophores obtained by sonication and a heavy fraction which appeared in electron micrographs to consist of cell fragments which were designated as heavy chromatophores and were composed of broken cell envelopes containing closely packed vesicles enclosed within the cytoplasmic membrane. Both types of chromatophores catalyzed photophosphorylation. However, cytochrome c2 could be washed out only from the heavy chromatophores. Photophosphorylation activity which was lost by the removal of the cytochrome could be restored by addition of either cytochrome c2 or phenazine methosulphate. Light induced proton efflux in heavy chromatophores in contrast to proton influx in regular chromatophores. The washed heavy chromatophores did not lose the light induced proton movement. Light induced quenching of 9-aminoacridine and atebrin fluorescence in chromatophores, while the fluorescence was enhanced in the heavy chromatophores. The washing did not affect the fluorescence changes of the heavy chromatophores but caused a reduction of the steady state of the carotenoid absorbance shift. It is suggested that the membrane in the heavy chromatophores is oriented inside out with respect to the membrane in regular chromatophores. Cytochrome c2 which is attached to that side of the membrane facing the outside medium could be removed from the heavy chromatophors and reconstituted to them. The role of cytochrome c2 in photophosphorylation is discussed.

The Ultrastructure of Erythrophores and Melanophores from the Skin ofTilapia mossambica(Peters)

The ultrastructure of erythrophores and melanophores present in the skin of adult Tilapia mossambica is described. A comparison of the two types of chromatophores indicates that both show a smooth endoplasmic reticulum, pinocytotic vesicles, microtubules and complexly branching cell processes. However, differences in the form, consistency and distribution of erythrosomes and melanosomes are noted. It is suggested that erythrophores be defined as chromatophores including carotenoid derivatives as the main pigment in their erythrosomes.

Behavior of chromatophores of the fiddler crab Uca pugilator and the dwarf crayfish Cambarellus shufeldti in response to synthetic Pandalus red pigment-concentrating hormone

Synthetic Pandalus red pigment-concentrating hormone was effective in concentrating the pigment in the erythrophores of the fiddler crab Uca pugilator and the dwarf crayfish Cambarellus shufeldti. However, this hormone had no effect on the melanophores of the crab or the leucophores of the crab and crayfish. These results are in accord with the hypothesis that in the fiddler crab and the dwarf crayfish, respectively, the hormonal control for each type of chromatophore is different.

Fluorescence polarization and pigment orientation in photosynthetic bacteria

Fluorescence polarization of photosynthetic bacteria with various types of chromatophores suggests an orientation of bacteriochlorophylls, but not of carotenoids. Comparison of the in vitro fluorescence polarization spectra of bacteriochlorophyll at high and low concentration and at 77 °K with those in vivo at various temperatures and in the presence of carbowax indicates that dichroism of shape effects the in vivo spectra. Both orientation and shape effects are highest for bacteria containing lamellar-type chromatophores, and lowest in those containing vesicle-type ones. The polarization values of the bacteria studied are similar for the various red bands, indicating a nearly parallel orientation of the adjacent bacteriochlorophylls.

Effect of cytochalasin B on the response of the chromatophores of isolated frog skin to MSH, theophylline, and dibutyryl cyclic AMP

Cytochalasin B is confirmed as reversibly inhibiting melanin dispersion in the melanophores of isolated frog skin in response to MSH. In addition, iridophore contraction is inhibited, as well as the responses of both types of chromatophores to theophylline or dibutyryl cyclic AMP, suggesting that melanin dispersion and iridophore contraction may occur as a result of the effect of cyclic AMP on microfilament function.

Elektronenoptische Untersuchungen an Flechten

The substructure in the phycobionts of the genus Trebouxia from different lichens is analysed. In the group Trebouxia I and Trebouxia II a further classification according to the differentiation of the chromatophores and their pyrenoids can be made. Trebouxia I: 1. Very long thylakoids are piled together. A few thylakoids curve through the pyrenoid. 2. The thylakoids are arranged like grana- and stromathylakoids in higher plants. In the pyrenoid the thylakoids are extended to “canals”. Trebouxia II: 1. Long thylakoids are packed very close together. A few of them pass through the pyrenoid in regular intervals. 2. The thylakoids are single or in piles. In the pyrenoid the thylakoids are again extended to “canals”. 3. The thylakoids are enlarged to vesicles which extend into the pyrenoid in the same form. 4. The thylakoids show all different forms of the above mentioned differentiations. In the different types of chromatophores there are always a large number of osmiophilic plastoglobuli in the pyrenoid matrix. It is discussed whether they are a reservoir in the lipid metabolism of the lichens.

Die Reaktion der Chromatophoren des Seeigels Centrostephanus longispinus auf Licht

1. When stimulated with white light of intensity between 0,4 and 53 Lux the chromatophores on isolated spine bases of Centrostephanus longispinus show a degree of pigment dispersion which is proportional to the light intensity (Fig. 2). 2. With stronger intensities, light induces a maximal pigment dispersion; darkness causes a maximal pigment concentration. Concentration is quicker than dispersion. In different chromatophore stages both processes differ in the forms of pigment distribution (Fig. 3). 3. The most common chromatophores are brown but there are also violet and yellow ones; they differ in the size and form of the pigment granules. With the method employed a difference in the reaction to white light could not be demonstrated. Possibly they are different developmental stages of one single type of chromatophore.

A New Green Tree Frog from Suriname

AMONG the many bright green tree frogs in South America the green coloration may be brought about by two entirely different sets of physiological factors. In one type the skin contains three types of chromatophores arranged in different layers. The most superficial layer is made up of lipophores that are filled with a yellow, fatty material. Deep to the lipophores is a layer of guanophores packed with crystals of guanine, a chemical allied to uric acid. The deepest layer is that of the melanophores. When visible light falls on the skin the light of shorter wave lengths (greens, blues, lavenders) is reflected back by the guanophores while the longer wave lengths (reds, oranges, yellows) are absorbed by the melanophores. As the shorter light rays are reflected by the guanophores back through the lipophores the blues and lavenders tend to be absorbed while the greens are transmitted so that the skin appears green to the human eye. If, however, the lipophores are altered or destroyed by preserving fluid the blues and lavenders are transmitted so that the preserved frog appears blue or some shade of lavender to the human eye. Examples of skin pigmentation of this type are found in Phyllomedusa bicolor (blue in preservative), Phyllomedusa hypochondrialis, and Centrolenella geijskesi (lavender in preservative). In addition to green frogs of this type there are others in which the green coloration is due to an accumulation of a chemical (biliverdin) in the skin rather than to chromatophores. In this latter group the chemical may be altered or destroyed by the preserving fluid so that the specimen fades to a milky white. As examples of this type we can mention Hyla punctata, Hyla granosa, and Sphoenorhynchus aurantiacus. It is one of the latter type that we describe here.

The dermal chromatophore unit.

Rapid color changes of amphibians are mediated by three types of dermal chromatophores, xanthophores, iridophores, and melanophores, which comprise a morphologically and physiologically distinct structure, the dermal chromatophore unit. Xanthophores, the outermost element, are located immediately below the basal lamella. Iridophores, containing light-reflecting organelles, are found just beneath the xanthophores. Under each iridophore is found a melanophore from which processes extend upward around the iridophore. Finger-like structures project from these processes and occupy fixed spaces between the xanthophores and iridophores. When a frog darkens, melanosomes move upward from the body of the melanophore to fill the fingers which then obscure the overlying iridophore. Rapid blanching is accomplished by the evacuation of melanosomes from these fingers. Pale coloration ranging from tan to green is provided by the overlying xanthophores and iridophores. Details of chromatophore structure are presented, and the nature of the intimate contact between the chromatophore types is discussed.

Stimulation of melanophores and guanophores by melanophore-stimulating hormone peptides

Both melanophores and guanophores are under the control of hypophysial chromatotropic hormone (CTH, MSH, MDH, intermedin, etc.). This principle induces melanophore expansion and guanophore contraction. In order to compare the structural requirements of CTH for both melanophore and guanophore responses, the efficacy of various MSH peptides on each of these reactions was tested in hypophysioprivic larvae of Rana pipiens and Rana sylvatica. Peptides tested included two pentapeptides, a hexapeptide, a heptapeptide, an octapeptide, two decapeptides, bovine α-MSH, bovine β-MSH, and a substituted synthetic α-MSH. Both melanophores and guanophores responded to all the peptides tested. Responses to the shorter peptides were far weaker than those induced by the complete molecule; however, in all cases melanophore and guanophore reactions paralleled one another. The same proportional degree of response holds for peptides which have been “potentiated” by alkali treatment. These observations imply that common features of the MSH molecule are involved in the stimulation of both types of chromatophores.

The dermal light sense.

Summary1. Dermal light reactions are responses to illumination of the body surface of animals due to stimulation of diffusely distributed photoreceptors.2. They are found in all major phyla, being most common in aquatic animals with non‐waterproof skins. They are rare in terrestrial arthropods, cephalopods and amniotes.3. An animal may possess a dermal light sense in addition to eyes or other localized photoreceptors.4. Responses to dermal stimulation may be local or general, graded or all‐or‐none. They include direct responses to light of some chromatophores, slow orientations by bending movements and many fast withdrawal reflexes.5. Locomotion in many animals is controlled photokinetically by dermal receptors. The relation between intensity and the speed of locomotion is usually an orthokinesis but in some planarians and the ammocoete larva it is a klinokinesis.6. There is evidence for orientated control of locomotion by dermal receptors in planarians and some lower vertebrates.7. Reaction times of dermal responses are relatively long. Except in Metridium, the reaction time consists of a sensitization and a latent period, the relationship between which is complex.8. Dermal and optic responses exhibit similar physiological characteristics. Dermal light reactions adapt to repeated and continuous stimuli, show considerable powers of dark adaptation and obey Weber's Law over a limited range of intensity.9. The absolute sensitivity of dermal photoreceptor systems is several thousand times less than that of well‐developed eyes.10. Action spectra are generally similar to those of eyes, with maximum sensitivity usually between 470 and 530 mμ. The photochemical systems responsible for all light reactions are believed therefore to be of a similar nature.11. No single receptor system at the cellular level of organization can account for all types of dermal light reactions.12. There is evidence that the protoplasm of a variety of cells in Metazoa is sensitive to light. The parietal muscles of Metridium, the ectodermal nerve net of Diadema and some types of chromatophores have been found to be light‐sensitive.13. The light reactions of blind cave‐dwelling teleosts show some unusual features which may be related to a comparatively recent loss of functional eyes.14. There is no convincing evidence of fundamental differences in the processes responsible for dermal and optic light responses, nor for the existence of more than one type of dermal photoreceptors in any species.15. A common structural basis for all light reactions, if it exists, must be sought in the fine structure of cells.I am most grateful to my colleagues who have read the manuscript. I wish to acknowledge my gratitude to Professor P. B. Medawar, F.R.S., for hospitality in the Zoology Department of University College, London, where much of the work on this article was done.

ENDOCRINE CONTROL IN THE CRUSTACEA

ENDOCRINE CONTROL IN THE CRUSTACEA

Enzymatic inactivation of the pigment hormone of the crustacean sinus gland.

SEVERAL investigators have reported a dispersion of the concentrated red and yellow pigments in light-adapted species of Leander by injecting various tissue extracts. Panouse1 brought about a weak and slow dispersion by injecting extracts of “connectifs cerebro-œsophagiens”, an effect that was considered not to be hormonal. Sunesson2 announced similar results when extracts from the head of the isopod Idothea neglecta were used; but only one type of the chromatophores reacted in this way. Repeating these experiments, Carstam and Sunesson3 confirmed Sunesson's statement; but when extracts of the caudal segments were injected, the pigments of both types of chromatophores were clearly dispersed. The pigment movement, however, was different from the hormonally regulated pigment concentration in being slower, and a maximal effect was never obtained even if concentrated extracts were used.

The comparative effects of teleost and beef pituitary on chromatophores of cold-blooded vertebrates.

1. Fish and beef acetone-desiccated pituitaries cause a distal migration of pigment granules in melanophores when injected into the elasmobranch Urobatis halleri, the teleost Ameiurus melas, the amphibians Hyla regilla and Rana pipiens, and the reptile Anolis carolinensis. These preparations not only disperse melanin but also induce a proximal migration of the white granules in leucophores of Rana pipiens larvae.2. Fish pituitary injected into the teleosts Gambusia affinis, Fundulus parvipinnis, Girella nigricans, Gillichthys mirabilis, Lepomis cyanellus and Leuresthes tenuis causes a proximal migration of melanin and, at least in the first three species, a distal migration of pigment in the xanthophores. Desiccated fish brain, beef whole gland, beef posterior lobe and commercial pituitrin have no obvious effect on their chromatophores.3. There is an opposite migration of melanin in certain different species of teleosts treated with fish pituitary. The diverse chromatic reaction of teleosts may have phylogenetic significance. The more primitive teleosts appear to react like other classes of cold-blooded vertebrates, whereas the higher teleosts, which have diverged more from the common line of vertebrate evolution, do not.4. There is a differential in reaction of different types of chromatophores in a single species to treatment with the same pituitary preparations.5. Pituitary material from different sources may have unlike chromatophorotropic action. Beef and fish pituitary have a similar action (expansion) on melanophores of Urobatis, Ameiurus, Rana and Anolis. However, on such teleosts as Fundulus and Girella, fish extracts have the opposite effect and mammalian extracts have no apparent effect.

Animal Colour Changes and their Neurohumours

THIS is a very valuable compilation of literature A on chromatic function which, together with previous reviews by Fuchs (1910) and Hogben (1924), makes readily accessible all references on the subject from antiquity to recent times. The introductory chapter deals with distribution and types of chromato-phores, with their activities and methods of measuring them. This is followed by a systematic survey of chromatic response in cephalopods, Crustacea and cold-blooded vertebrates ; seasonal coat changes in birds and mammals are not discussed. The final chapters consider development, genetics and ‘special activities' of vertebrate chromatophores. The bibliography of more than 1,200 titles is conveniently arranged under three heads, namely, surveys, publications (chiefly historical) before 1910, and a complete list from 1910 to 1943 inclusive. As we have learned to expect from Prof. Parker, the script is lucidly and persuasively written. Animal Colour Changes and their Neurohumours A Survey of Investigations, 1910– 1943. By George Howard Parker. Pp. x + 377. (Cambridge : At the University Press, 1948.) 30s. net.

Chromatophore types in crago and their endocrine control

Chromatophore types in crago and their endocrine control

QUANTITATIVE CHANGES IN PIGMENTATION, RESULTING FROM VISUAL STIMULI IN FISHES AND AMPHIBIA1

SummaryFishes and, in lesser degree, Amphibia respond to backgrounds in such a manner that their shade, and to a certain extent their colour, tend to conform to that of the substratum on which they lie, or over which they swim. The integrity of the eyes and of major portions of the nervous system is essefitial to these phenomena.The immediate, transitory or “physiological” dour changes are due to the rearrangement of pigment particles already present. When the effective stimuli are continued for some days or weeks, changes become evident both in the number of chromatophores and in the pigment contents of each (quantitative or “morphological” colour changes).All three of the types of chromatophores (melanophores, guanophores, lipo‐phores) are affected by these changes. Dark backgrounds favour the production of melanin and inhibit the production of guanin. Pale backgrounds have a reverse effect. In fishes at least, production (or retention) of the yellow pigment xantho‐phyll is favoured by black backgrounds and retarded by white ones, agreeing thus with melanin. To what extent there is any specific effect of coloured backgrounds (sensu stricto) upon the quantity of xanthophyll is not clear at present.Intensity of illumination, above a rather low level, has very little effect upon pigment formation in fishes. There is some evidence, however, of a slight degree of positive correlation between light intensity and melanin formation. Total darkness leads to pigment reduction both in fishes and Amphibia.Blinding of both eyes, in both of these groups, results in a marked increase of melanin, but only in animals which are kept in the light.Experiments involving illumination from below are known to have resulted in considerable increases in pigmentation of the ventral surface, both in fishes and Amphibia. It is not certain in these cases whether optic stimuli have been concerned, or whether the effects have been due to direct illumination of the skin.The response of a fish to its background is primarily a response to albedo, this being defined as the proportion of incident light which is reflected or dispersed from a given surface. On the basis of considerable evidence, a rule has been formulated which has been found to hold approximately, at least for certain fishes. This rule is that, when the animals are subjected to a variety of backgrounds, under uniform illumination, the amount of melanin (or the number of melanophores) produced varies inversely as the logarithm of the albedo of the background. The close analogy between these pigmentary responses of fishes, and the phenomena of sense perception in man for which the “Weber‐Fechner Law” was formulated was pointed out.The question of how a fish recognizes, and responds to, a given albedo, regardless of the absolute degree of illumination present, resolves itself into the question as to how the animal perceives the ratio between the source of light and the light reflected from the bottom and surrounding objects. This last does not seem to be so difficult an achievement when we consider that the ratio in question is ordinarily that between the upper and lower halves of the field of vision, or in other words, between the stimulus received by the lower and upper halves of the retina. Experimental evidence is accumulating showing that these two areas of the retina are functionally differentiated in the required manner.It was early recognized that those conditions which tend to bring about transitory colour changes are the same ones which, if prolonged, produce quantitative changes. The question has been raised whether the state of chromatophore “expansion” (pigment dispersal) per se, promotes pigment production and cell multiplication, and chromatophore “contraction” promotes the reverse processes, or whether both transitory and quantitative changes are the results of a common (probably hormonal) cause. The weight of present evidence probably favours the latter interpretation.The relative roles of direct nervous control of the chromatophores and control through hormones is still a subject of controversy, both for fishes and Amphibia. It now seems probable, not only that these two classes of animals differ from one another in important ways, but that the two major groups of fishes, elasmobranchs and teleosts, likewise differ from one another. Even within the group of elasmobranchs, moreover, important differences have been claimed. The whole subject is further complicated by the discovery that “direct” nervous control is itself probably mediated through hormones liberated by the nerve terminals. In general, it is now helieved that nervous control (with the reservation just indicated) is the one chiefly involved in the colour changes of teleosts, while control through blood‐borne hormones is chiefly involved in the colour changes of both elasmobranchs and Amphibia. But this statement oversimplifies the present state of the problem.