ON THE DISTRIBUTION OF VITAMINS A1 AND A2

The distribution of vitamins A₁ and A₂ has been determined in the eye tissues and livers of a number of fishes. The vitamins were differentiated by means of the antimony chloride reaction, which yields with A₁ a band at 615–620 mµ and with A₂ a band at about 696 mµ. In the retina the presence of vitamin A₁ is diagnostic of the operation of a rhodopsin, and vitamin A₂ of a porphyropsin cycle. The eye tissues of all permanently marine fishes examined, except the tautog, contain vitamin A₁ alone. Those of all permanently freshwater fishes possess only vitamin A₂. Those of all euryhaline (potentially migratory) fishes, except possibly the alewife, contain mixtures of both vitamins A, and always predominantly that one which ordinarily is associated with the environment in which the fish is spawned. These correlations extend in part to the liver oils, but most livers contain mixtures of both vitamins A, and occasionally in proportions the reverse of those in the eye tissues. The vitamin A configuration does not depend upon environmental circumstances, but is determined genetically. The transfer from vitamin A₁ to A₂ metabolism appears associated phylogenetically with migration of marine teleosts into fresh water.     

The metamorphosis of visual systems in the sea lamprey

The life cycle of the sea lamprey, Petromyzon marinus, includes two metamorphoses. At the end of a period spent as a blind larva, buried in the mud of streams, a first metamorphosis prepares it to migrate downstream to the sea or a lake for its growth phase. Then, following a second metamorphosis, it migrates upstream as a sexually mature adult to spawn and die. The downstream migrants have a visual system based upon rhodopsin and vitamin A₁, whereas that of the upstream migrants is based upon porphyropsin and vitamin A₂. The livers contain vitamin A₁ at all stages. The sea lamprey therefore exhibits a metamorphosis of visual systems, like those observed earlier among amphibia. The presence of porphyropsin in this member of the most primitive living group of vertebrates, as in fishes and amphibia, supports the notion that porphyropsin may have been the primitive vertebrate visual pigment. Its association with fresh water existence throughout this range of organisms also is consistent with the view that the vertebrate stock originated in fresh water. The observation that in the life cycle of the lamprey rhodopsin precedes porphyropsin is not at variance with the idea that porphyropsin is the more primitive pigment, since this change is part of the second metamorphosis, marking the return to the original environment. The observation that in lampreys, fishes, and amphibia, porphyropsin maintains the same general association with fresh water, and rhodopsin with marine and terrestrial habit, suggests that a single genetic mechanism may govern this association throughout this wide span of organisms.     

THE PORPHYROPSIN VISUAL SYSTEM

1. In the rods of fresh-water and some anadromous fishes, rhodopsin is replaced by the purple photolabile pigment porphyropsin. This participates in a retinal cycle identical in form with that of rhodopsin, but in which new carotenoids replace retinene and vitamin A. 2. Porphyropsin possesses a broad absorption maximum at 522 ± 2 mµ, and perhaps a minimum at about 430 mµ. The vitamin A-analogue, vitamin A₂, possesses a maximum in chloroform at 355 mµ and yields with antimony trichloride a deep blue color due to a band at 696 mµ. The retinene-analogue, retinene₂, absorbs maximally in chloroform at 405 mµ and possesses an antimony chloride maximum at 706 mµ. 3. Its non-diffusibility through a semi-permeable membrane, salting-out properties, and sensitivity to chemical denaturants and to heat, characterize porphyropsin as a conjugated carotenoid-protein. 4. The porphyropsin cycle may be formulated: porphyropsin See PDF for Structure. retinene₂-protein ₍₂₎ ^→ vitamin A₂-protein ₍₃₎ ^→ porphyropsin. Isolation of the retina cuts this cycle at (3); denaturation procedures or extraction of porphyropsin into aqueous solution eliminate in addition (1) and (2). 5. The primary difference between the rhodopsin and porphyropsin systems appears to be the possession by the latter of an added ethylenic group in the polyene chain.     

Rhodopsin and Porphyropsin Fields In the Adult Bullfrog Retina

Though it had been supposed earlier that the bullfrog undergoes a virtually complete metamorphosis of visual systems from vitamin A₂ and porphyropsin in the tadpole to vitamin A₁ and rhodopsin in the adult, the present observations show that the retina of the adult frog may contain as much as 30–40% porphyropsin, all of it segregated in the dorsal zone. The most dorsal quarter of the adult retina may contain 81–89% porphyropsin mixed with a minor amount of rhodopsin; the ventral half contains only rhodopsin. Further, the dorsal zone contains a two to three times higher concentration of visual pigments than the ventral retina. The pigment epithelium underlying the retina contains a corresponding distribution of vitamins A₁ and A₂, predominantly vitamin A₂ in the dorsal pigment epithelium, exclusively vitamin A₁ in the ventral zone. The retina accepts whatever vitamin A the pigment epithelium provides it with, and turns it into the corresponding visual pigment. Thus, a piece of light-adapted dorsal retina laid back on ventral pigment epithelium regenerates rhodopsin, whereas a piece of light-adapted ventral retina laid back on dorsal pigment epithelium regenerates predominantly porphyropsin. Vitamin A₂ must be made from vitamin A₁, by dehydrogenation at the 3,4-bond in the ring. This conversion must occur in the pigment epithelium, presumably through the action of a vitamin A-3,4-dehydrogenase. The essential change at metamorphosis is to make much less of this dehydrogenase, and to sequester it in the dorsal pigment epithelium. Some adult bullfrogs, perhaps characteristically taken in the summer, contain very little porphyropsin—only perhaps 5%—still sequestered in the dorsal retina. The gradient of light over the retinal surface has little if any effect on this distribution. The greater density of visual pigments in the dorsal retina, and perhaps also—although this is less clear—the presence of porphyropsin in this zone, has some ecological importance in increasing the retinal sensitivity to the dimmer and, on occasion, redder light received from below.     

THE VISUAL SYSTEMS OF EURYHALINE FISHES

1. The retinas of all marine fishes so far examined except the Labridae, and of all terrestrial vertebrates contain the rhodopsin system alone; those of fresh water fishes the porphyropsin system alone. In the present paper the visual systems of a number of euryhaline fishes are examined—fishes capable of existence in a wide range of salinities, though usually restricted in spawning either to the sea (catadromous) or to fresh water (anadromous). 2. The retinas of the anadromous salmonids (brook trout, rainbow trout, and chinook salmon) contain mixtures of the rhodopsin and porphyropsin systems, predominantly the latter. The retinas of the catadromous eel and the killifish also contain mixtures of both systems, but in reverse proportions. The retinas of the anadromous white perch and alewife contain the porphyropsin system alone. 3. There is therefore an extensive parallelism between the salinity relations of these animals and the composition of their visual systems. All of them possess predominantly or exclusively the visual system commonly associated with the environment in which the fish spawns. 4. These patterns are fixed genetically, and are to a first approximation independent of the history of the individual. They may represent transitional stages in the evolutionary migration of fishes to and from the sea. The presence of both types of visual system in the retinas of some euryhaline fishes incidentally satisfies one formal requirement of two-component color vision.     

The nature of the lamprey visual pigment

From the retina of the land-locked population of the sea lamprey, Petromyzon marinus, a photolabile pigment was extracted which was identified spectrophotometrically as a member of the rhodopsin group of pigments. Using the absorption spectrum of a relatively pure solution and analysis by means of difference spectra, the peak of this pigment was placed at about 497 mµ. The method of selective bleaching by light of different wave lengths revealed no significant amounts of any other pigment in the extracts. A similar pigment was also detected in retinal extracts of the Pacific Coast lamprey, Entospenus tridentatus. These results are significant for two reasons: (a) the lamprey is shown to be an example of an animal which spawns in fresh water but which is characterized by the presence of rhodopsin, rather than porphyropsin, in the retina; (b) the primitive phylogenetic position of the lamprey suggests that rhodopsin was the visual pigment of the original vertebrates.     

Molecular characterisation of prolactin and analysis of extrapituitary expression in the European sea bass Dicentrarchus labrax under various salinity conditions

Although prolactin has been demonstrated to be the main hormone involved in adaptation to dilute media in several freshwater teleosts, few studies have been conducted in marine teleosts. In the Mediterranean, the sea bass Dicentrarchus labrax inhabits environments ranging from the open sea to coastal lagoons, where salinity varies greatly. We characterised the prolactin (prl) gene and analysed its expression in two organs (gill and intestine) in D. labrax acclimated to either freshwater or seawater. A 2819 bp long sequence encompassing the prl gene and a part (282 bp) of the promoter were identified, and these comprised 5 coding exons separated by 4 introns. Prolactin was similarly expressed in fresh- and seawater adapted fish, although expression in gills was significantly greater than in the intestine. Nonetheless, individuals unable to successfully regulate osmotic balance in freshwater presented overall low expression rates. Results are discussed according to the mechanism of sea bass adaptation in the wild and to their life cycle between open sea and lagoons. Finally, a phylogenetic analysis indicated that teleosts are not branched according to their life-history features (e.g. seawater vs. freshwater habitats), and no signature of positive selection was detected across the phylogeny of the prl gene in teleosts.     

Gene Duplications and Evolution of Vertebrate Voltage-Gated Sodium Channels

Voltage-gated sodium channels underlie action potential generation in excitable tissue. To establish the evolutionary mechanisms that shaped the vertebrate sodium channel α-subunit (SCNA) gene family and their encoded Na_v1 proteins, we identified all SCNA genes in several teleost species. Molecular cloning revealed that teleosts have eight SCNA genes, compared to ten in another vertebrate lineage, mammals. Prior phylogenetic analyses have indicated that the genomes of both teleosts and tetrapods contain four monophyletic groups of SCNA genes, and that tandem duplications expanded the number of genes in two of the four mammalian groups. However, the number of genes in each group varies between teleosts and tetrapods, suggesting different evolutionary histories in the two vertebrate lineages. Our findings from phylogenetic analysis and chromosomal mapping of Danio rerio genes indicate that tandem duplications are an unlikely mechanism for generation of the extant teleost SCNA genes. Instead, analyses of other closely mapped genes in D. rerio as well as of SCNA genes from several teleost species all support the hypothesis that a whole-genome duplication was involved in expansion of the SCNA gene family in teleosts. Interestingly, despite their different evolutionary histories, mRNA analyses demonstrated a conservation of expression patterns for SCNA orthologues in teleosts and tetrapods, suggesting functional conservation. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Axel Meyer]     

Lactate Dehydrogenase Isozymes, Gytochrome Oxidase Activity, and Muscle Ions of the Rattail (Coryphaenoides sp.)

SYNOPSIS. Investigations into the behavior of molecules in organismsoccupying unique environments may provide a better insight intothe functions of these same molecules in organisms from morecommon habitats. An organism well suited for such analyses isthe rattail (Coryphaenoides sp.), a deep-sea teleost. The photoreceptorcells of the retina are predominantly rods. Although the lactatedehydrogenase A₁, and B₄, isozymes are present in this fish,the E₄ isozyme (found in the retina of many teleosts) is absentin the rattail retina. The rattails possess a lower cytochromeoxidase activity than shallow water fish. The sodium concentrationis higher, and the potassium concentration lower in the rattailas compared with surface marine fish. The patterns of molecularsynthesis and concentrations in the rattail may be related tosuch factors as light intensity, hydrostatic pressure, and temperaturewhich exists in the deep-sea environment.     

A Systematic Survey of the Occurrence of the Hypothalamic Saccus Vasculosus in Teleost Fish

The saccus vasculosus (SV) was examined histologically in more than 200 species of teleosts. The Atherinomorpha (Cyprinodontiformes and Atheriniformes) completely lack the SV. Many primary freshwater teleosts (Osteoglossiformes, Cypriniformes, Characiformes, Siluriformes, Gymnotiformes, and Synbranchiformes) possess none or a reduced SV. Some secondary freshwater teleosts also possess a reduced SV, but other secondary freshwater teleosts have a well-developed SV. Some marine teleosts swimming in the surface water, for example, the Clupeiformes and Scombridae, possess a somewhat reduced SV. Bathypelagic teleosts also possess a rather reduced SV. On the other hand, most marine teleosts, benthic or nektonic in the subsurface water, have a well-developed SV. The examples are the Anguilliformes, Scorpaeniformes, Perciformes, Pleuronectiformes, and Tetraodontiformes. Since all non-teleostean actinopterygians possess a well-deveoped SV, it is assumed that the earliest teleosts also possessed a SV. In the course of adaptive radiation, some teleost groups certainly have reduced or lost the SV while others developed it to various degrees. Reduction or development of the SV might be influenced more easily by environments in certain groups and might be constrained more strongly by phylogenetic lineages in other groups.     

Lampreys Have a Single Gene Cluster for the Fast Skeletal Myosin Heavy Chain Gene Family

Muscle tissues contain the most classic sarcomeric myosin, called myosin II, which consists of 2 heavy chains (MYHs) and 4 light chains. In the case of humans (tetrapod), a total of 6 fast skeletal-type MYH genes (MYHs) are clustered on a single chromosome. In contrast, torafugu (teleost) contains at least 13 fast skeletal MYHs, which are distributed in 5 genomic regions; the MYHs are clustered in 3 of these regions. In the present study, the evolutionary relationship among fast skeletal MYHs is elucidated by comparing the MYHs of teleosts and tetrapods with those of cyclostome lampreys, one of two groups of extant jawless vertebrates (agnathans). We found that lampreys contain at least 3 fast skeletal MYHs, which are clustered in a head-to-tail manner in a single genomic region. Although there was apparent synteny in the corresponding MYH cluster regions between lampreys and tetrapods, phylogenetic analysis indicated that lamprey and tetrapod MYHs have independently duplicated and diversified. Subsequent transgenic approaches showed that the 5′-flanking sequences of Japanese lamprey fast skeletal MYHs function as a regulatory sequence to drive specific reporter gene expression in the fast skeletal muscle of zebrafish embryos. Although zebrafish MYH promoters showed apparent activity to direct reporter gene expression in myogenic cells derived from mice, promoters from Japanese lamprey MYHs had no activity. These results suggest that the muscle-specific regulatory mechanisms are partially conserved between teleosts and tetrapods but not between cyclostomes and tetrapods, despite the conserved synteny.     

Nutritional effect of freshwater Chlorella on growth of the rotifer Brachionus plicatilis

Mass production of Brachionus plicatilis is usually accomplished by feeding so-called marine Chlorella (Nannochloropsis oculata) to the rotifers in marine fish hatcheries. If the marine Chlorella are in short supply, baker's yeast is usually used as a supplementary food. Recently, a condensed suspension of freshwater Chlorella (Chlorella vulgaris, k-22) was commercially developed as another supplementary food. We have evaluated the dietary value of this freshwater Chlorella for growth of the rotifer by means of individual and batch cultures. Rotifers cultured with the freshwater Chlorella suspension under almost bacteria-free conditions, showed very suppressed growth. However if the Chlorella was supplemented with vitamin B₁₂ by adding the vitamin solution into the suspension or by culturing the Chlorella in a medium containing vitamin B₁₂, the nutritional value of freshwater Chlorella was greatly improved and almost at the same level as that of marine Chlorella. Condensed Chlorella may therefore be effective as a supplementary food if vitamin B₁₂ is supplied.     

Ureogenesis in a freshwater teleost: an unusual sub-cellular localization of ornithine-urea cycle enzymes in the freshwater air-breathing teleost Heteropneustes fossilis.

Sub-cellular localization of different ornithine-urea cycle enzymes was studied in the liver and kidney of a freshwater air-breathing teleost. Carbamyl phosphate synthetase, ornithine transcarbamylase, and arginase were found to be localized inside the mitochondria, and argininosuccinate synthetase and argininosuccinate lyase were found in the soluble fraction. Mitochondrial localization of arginase, a feature known in marine elasmobranchs and toadfishes, indicates the evolutionary position of H. fossilis to be different from that of present day freshwater teleosts.     

CAROTENOIDS AND THE VISUAL CYCLE

1. Carotenoids have been identified and their quantities measured in the eyes of several frog species. The combined pigment epithelium and choroid layer of an R. pipiens or esculenta eye contain about 1γ of xanthophyll and about 4γ of vitamin A. During light adaptation the xanthophyll content falls 10 to 20 per cent. 2. Light adapted retinas contain about 0.2–0.3 γ of vitamin A alone. 3. Dark adapted retinas contain only a trace of vitamin A. The destruction of their visual purple with chloroform liberates a hitherto undescribed carotenoid, retinene. The bleaching of visual purple to visual yellow by light also liberates retinene. Free retinene is removed from the isolated retina by two thermal processes: reversion to visual purple and decomposition to colorless products, including vitamin A. This is the source of the vitamin A of the light adapted retina. 4. Isolated retinas which have been bleached and allowed to fade completely contain several times as much vitamin A as retinas from light adapted animals. The visual purple system therefore expends vitamin A and is dependent upon the diet for its replacement. 5. Visual purple behaves as a conjugated protein in which retinene is the prosthetic group. 6. Vitamin A is the precursor of visual purple as well as the product of its decomposition. The visual processes therefore constitute a cycle.     

Variations in the presence of chloride cells in the gills of lampreys (Petromyzontiformes) and their evolutionary implications

Although confined to fresh water, non‐parasitic species of lampreys and the landlocked parasitic sea lamprey, all of which were derived relatively recently from anadromous ancestors, still develop chloride cells, whose function in their ancestors was for osmoregulation in marine waters during the adult parasitic phase. In contrast, such cells are not developed by the non‐parasitic least brook lamprey Lampetra aepyptera, which has been separated from its ancestor for >2 million years, nor by the freshwater parasitic species of the genus Ichthyomyzon. The length of time that a non‐parasitic species or landlocked parasitic form or species has spent in fresh water is thus considered the overriding factor determining whether chloride cells are developed by those lampreys.     

Evolution of opercle bone shape along a macrohabitat gradient: species identification using mtDNA and geometric morphometric analyses in neotropical sea catfishes (Ariidae)

Transitions between the marine and freshwater macrohabitat have occurred repeatedly in the evolution of teleost fishes. For example, ariid catfishes have moved from freshwater to marine environments, and vice versa. Opercles, a skeletal feature that has been shown to change during such transitions, were subjected to 2D geometric morphometric analyses in order to investigate evolutionary shape changes during habitat transition in ariid catfishes and to test the influence of habitat on shape changes. A mtDNA marker, which proved useful in previous studies, was used to verify species identities. It greatly improved the assignment of specimens to a species, which are difficult to assign by morphology alone. The application of a mtDNA marker confirmed the occurrence of Notarius biffi in Central America, South of El Salvador. Molecular identification together with principal component analysis (PCA) and further morphological inspection of neurocrania indicated the existence of a cryptic species within Bagre pinnimaculatus. Principal component (PC) scores of individual specimens clustered in morphospace by genus rather than by habitat. Strong phylogenetic structure was detected using a permutation test of PC scores of species means on a phylogenetic tree. Calculation of Pagel's λ suggested that opercle shape evolved according to a Brownian model of evolution. Yet canonical variate analysis (CVA) conducted on the habitat groups showed significant differences in opercle shapes among freshwater and marine species. Overall, opercle shape in tropical American Ariidae appears to be phylogenetically constrained. This verifies the application of opercle shape as a taxonomic tool for species identification in fossil ariid catfishes. At the same time, adaptation to freshwater habitats shows characteristic opercle shape trajectories in ariid catfishes, which might be used to detect habitat preferences in fossils.     

Alternative migration and host parasitism strategies and their long-term stability in river lampreys from the River Endrick, Scotland

The stability of a discrete body size dimorphism of sexually mature river lamprey Lampetra fluviatilis from the River Endrick, Scotland, was examined over a 21 year period. Stable isotope analysis was used to test the hypothesis that the two size forms comprise individuals with differing migration and parasitic foraging strategies. Maturing river lamprey and the brook lamprey Lampetra planeri were trapped over 3 months each year in the periods 1983–1984 and 2004–2005. Brook lamprey catches and catches of both species combined showed no significant trend in catch rate with time. The catch rate of small body size river lamprey declined between 1983–1984 and 2004–2005 (although the difference did not reach statistical significance; P = 0·055). In contrast, there was a significant increase in the catch rate of the large body size river lamprey and as a consequence, a significant change in the relative proportion of each of the two river lamprey morphs over the study period. Analysis of the stable isotopes of C and N in muscle tissue showed that brook lamprey tissue derived its carbon from a freshwater source and had a δ¹³C more consistent with that of the River Endrick than with Loch Lomond. δ¹⁵N values for this species showed it to be feeding at the base of the food chain, consistent with filter feeding as an ammocoete. The large body size and the small body size river lamprey adults differed substantially in their δ¹³C values, with the small body size δ¹³C signature indicative of a freshwater carbon source and the large body size morph of a marine source. The small body size morph had a δ¹³C signature that was consistent with that of Loch Lomond powan Coregonus lavaretus suggesting that they share a common carbon source. The large body size morph was clearly feeding at a higher trophic level than the small body size morph. A single small body size river lamprey individual with typical morphology for that group, however, had C and N signatures that clustered with those of the large body size morphs. This individual had either migrated to sea to forage, as is typical for the species, or had been feeding on an anadromous fish with a strong marine C signature in fresh water. It is concluded that the body size dimorphism is indicative of a differential migration and foraging strategy in the parasitic phase of the life cycle of river lamprey at this site.     

Carcass analogues provide marine subsidies for macroinvertebrates and juvenile Atlantic salmon in temperate oligotrophic streams

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Contrasting population genetic structure among freshwater‐resident and anadromous lampreys: the role of demographic history,differential dispersal and anthropogenic barriers to movement

The tendency of many species to abandon migration remains a poorly understood aspect of evolutionary biology that may play an important role in promoting species radiation by both allopatric and sympatric mechanisms. Anadromy inherently offers an opportunity for the colonization of freshwater environments, and the shift from an anadromous to a wholly freshwater life history has occurred in many families of fishes. Freshwater‐resident forms have arisen repeatedly among lampreys (within the Petromyzontidae and Mordaciidae), and there has been much debate as to whether anadromous lampreys, and their derived freshwater‐resident analogues, constitute distinct species or are divergent ecotypes of polymorphic species. Samples of 543 European river lamprey Lampetra fluviatilis (mostly from anadromous populations) and freshwater European brook lamprey Lampetra planeri from across 18 sites, primarily in the British Isles, were investigated for 13 polymorphic microsatellite DNA loci, and 108 samples from six of these sites were sequenced for 829 bp of mitochondrial DNA (mtDNA). We found contrasting patterns of population structure for mtDNA and microsatellite DNA markers, such that low diversity and little structure were seen for all populations for mtDNA (consistent with a recent founder expansion event), while fine‐scale structuring was evident for nuclear markers. Strong differentiation for microsatellite DNA loci was seen among freshwater‐resident L. planeri populations and between L. fluviatilis and L. planeri in most cases, but little structure was evident among anadromous L. fluviatilis populations. We conclude that postglacial colonization founded multiple freshwater‐resident populations with strong habitat fidelity and limited dispersal tendencies that became highly differentiated, a pattern that was likely intensified by anthropogenic barriers.     

The photosensitive retinal pigments of fishes from relatively turbid coastal waters

Digitonin extracts have been prepared from the retinae of a dozen species of marine and euryhaline teleost fishes from turbid water habitats. Spectrophotometric analysis of the extracts shows that the photosensitive retinal pigments of these species have maximum absorption above 500 mµ. In nine species there are retinene₁ pigments with λ_max between 504 and 512 mµ. In the marine but euryhaline mullet, Mugil cephalus, there is a porphyropsin with λ_max 520 mµ. A mixture of rhodopsin and porphyropsin in an extract of a marine puffer, Sphoeroides annulatus, was disclosed by partial bleaching with colored light. In addition, one other species has a 508 mµ pigment, of which the nature of the chromophore was not determined. The habitats in which these fishes live are relatively turbid, with the water greenish or yellowish in color. The spectral transmission of such waters is probably maximal between 520 and 570 mµ. It is suggested that the fishes have become adapted to these conditions by small but significant shifts in spectral absorption of their retinal pigments. These pigments are decidedly more effective than rhodopsin in absorption of wavelengths above 500 mµ. This offers a possible interpretation of the confusing array of retinal pigments described from marine and euryhaline fishes.