Post-metamorphic change in activity metabolism of anurans in relation to life history

Summary Newly-metamorphosed individuals of some species of frogs and toads differ from adults in behavior, ecology, and physiology. These differences may be related to broader patterns of the life histories of different species of frogs. In particular, the length of larval life and the size of a frog at metamorphosis appear to be significant factors in post-metamorphic ontogenetic change. These changes in performance are associated with rapid post-metamorphic increases in oxygen transport capacity. Bufo americanus (American toads) and Rana sylvatica (wood frogs) spend only 2–3 months as tadpoles and metamorphose at body masses of 0.25 g or less. Individuals of these species improve endurance and aerobic capacity rapidly during the predispersal period immediately following metamorphosis. Increases in hematocrit, hemoglobin concentration, and heart mass relative to body mass are associated with this improvement in organismal performance. Rana clamitans (green frogs) spend from 3 to 10 months as larvae and weigh 3 g at metamorphosis. Green frogs did not show immediate post-metamorphic increases in performance. Rana palustris (pickerel frogs) are intermediate to wood frogs and green frogs in length of larval life and in size at metamorphosis, and they are intermediate also in their post-metamorphic physiological changes.American toads and wood frogs appear to delay dispersal from their natal ponds while they undergo rapid post-metamorphic growth and development, whereas green frogs disperse as soon as they leave the water, even before they have fully absorbed their tails. The very small body sizes of newly metamorphosed toads and wood frogs appear to limit the scope of their behaviors. The brief larval periods of these species permit them to exploit transient aquatic habitats, but impose costs in the form of a period of post-metamorphic life in which their activities are restricted in time and space compared to those of adults.     

Activity metabolism of the toad (Bufo americanus): Ecological consequences of ontogenetic change

Summary Following metamorphosis, juvenile toads form dense, heliothermic aggregations on the margins of the ponds from which they emerge. After a period of growth and development, during which body mass increases ten-fold, the juveniles disperse from the pond and assume the solitary, nocturnal habits that characterize adult toads.The dispersal of the toads coincides with the culmination of ontogenetic changes in activity metabolism. Unlike adults, juvenile toads exhaust rapidly when exercised and exhibit a low aerobic component of total metabolic scope. Values of aerobic scope for sustained activity ranged from 0.5 ml O₂/(g·h) for the smallest juveniles to 1.0 ml O₂/(g·h) for adults. The capacity of juveniles for oxygen consumption increases rapidly with growth, reaching the level of mature animals immediately prior to dispersal.In contrast to aerobic metabolism, anaerobic scope was independent of body size. Whole body lactate content after a 1 min bout of vigorous activity was elevated above the resting level by 0.14 mg lactate/g for both juvenile and adult animals.The elevated body temperatures that are achieved by basking juvenile toads probably hasten their physiological development and increase their capacity for aerobic metabolism.     

Retrofitting larval neuromuscular circuits in the metamorphosing frog

Maturation of vertebrate neuromuscular systems typically occurs in a continuous, orderly progression. After an initial period of developmental adjustment by means of cell death and axonal pruning, relatively stable relationships, with only subtle modifications, are maintained between motoneurons and their appropriate targets throughout life. However, among a restricted group of vertebrates (amphibians and especially the anuran amphibians) the sequential maturation of neuromuscular systems is altered by an abrupt reordering of the basic body plan that encompasses cellular changes in all tissues from skeleton to nervous system. Many anuran amphibians possess neuromuscular circuits that are remarkable by virtue of their complete reorganization during the brief span of metamorphosis. During this period motor systems initially designed for the behavioral patterns of aquatic tadpoles are adjusted to meet the drastically different motor activities of postmetamorphic terrestrial life. This adjustment involves the deletion of neural elements mediating larval specific activities, the accelerated maturation of neural circuits eliciting adult-specific activities and the retrofitting of larval neuromuscular components to serve postmetamorphic behaviors. This review focuses on the cellular events associated with the neuromuscular adaptation in the jaw complex during metamorphosis of the leopard frog, Rana pipiens. As part of the metamorphic reorganization of the jaw apparatus there is a complete turnover of the myofiber complement of the adductor mandibulae musculature. Trigeminal motoneurons initially deployed to the larval myofibers are redirected to new muscle fibers. Simultaneously the cellular geometry and synaptic input to these motoneurons is revamped. These changes suggest that trigeminal neuromuscular circuitry established during embryogenesis is updated during metamorphosis and reused to provide the basis for adult jaw motor activity that is far different than its larval counterpart.     

Ecological correlates of anuran exercise physiology

Summary Studies of exercise physiology of anuran amphibians have led to the suggestion that there is a dichotomy between species that depend upon movement to escape from predators and species that utilize static defenses. This generalization has been based upon a limited taxonomic survey and it contrasts with morphological, ecological, and behavioral studies that have revealed diverse and complex interrelationships among these features of anuran biology. We tested the hypothesis of a dichotomy of physiological types among anurans by measuring aerobic and anaerobic metabolism during maximum exercise for 17 species representing seven families and a variety of ecological types and locomotor modes. All degrees of dependence upon aerobic and anaerobic power input were found among the 17 species and the variation did not follow phylogenetic divisions. No single, simple prediction of the predominant source of power utilized for activity by the anurans we studied is possible. Predator avoidance behavior was not significantly correlated with the metabolic pattern. Predatory mode (active versus passive searchers) and mode of locomotion (non-jumpers versus jumpers) were correlated with dependence upon aerobic energy production and with each other. Reproductive behavior is probably another associated factor. The diversity of modes of power input among anurans is great and is intimately linked with numerous features of a species' biology. Single-factor explanations of this physiological characteristic are not appropriate.     

Ontogeny of the Thyroid Glands During Larval Development of South American Horned Frogs (Anura,Ceratophryidae)

The role of thyroid hormone (TH) in anuran metamorphosis has been documented from a variety of approaches, but the sequence of morpho-histological development of the thyroid glands that produce the secretion of the hormone was assumed invariant from studies of relatively few species even when the effects of environmental influences on larval development and metamorphosis have been largely documented. There are anurans in which developmental and growth rates diverge, and the resulting heterochrony in growth and development produces giant/miniature tadpoles, and or rapid/delayed metamorphosis suggesting changes of the activity of the thyroid glands during larval development. Herein, we analyze the morpho-histological variation of the thyroid glands in larval series of Ceratophrys cranwelli, Chacophrys pierottii, Lepidobatrachus laevis and L. llanensis that share breeding sites along semiarid environments of the Chaco in South America, belong to a monophyletic lineage, and present accelerated patterns in growth and development in order to have a morphological evidence about a possible shift of TH physiology. We describe gross morphology and histology of the thyroid glands and find features shared by all studied species such as the presence of supernumerary heterotopic follicles; changes in the volume and number of follicles towards the metamorphic climax, and cuboidal epithelia with occasional intra-cellular vacuoles as signs of low glandular activity without a manifest peak at the climax as it was assumed for anurans. We discuss different lines of evidence to interpret sources of extra supplement of TH to support the rapid metamorphosis. These interpretations highlight the necessity to design a research program to investigate the endocrine variation during development of ceratophryids taking in account their morphology, physiology and ecology in order to learn more about the effects of environmental and developmental interactions involved in the anuran evolution.     

Swimming performance, metabolic rates, and their correlates in the Iceland scallop Chlamys islandica

The dramatic escape response of some scallops is modified by reproductive investment and by acclimation temperature. Despite considerable knowledge of the physiology of the escape response, functional links between escape response performance, organismal rates of oxygen uptake, and tissue metabolic capacities are little known. We measured oxygen consumption rates (standard, maximal, and aerobic scope), escape behavior (initial and repeat performance), tissue mass, condition index, protein content, and tissue metabolic capacities in the Iceland scallop Chlamys islandica to examine links between these parameters. Postexercise oxygen consumption rates were positively linked to contraction rate (repeat test) and to pyruvate kinase activity in the adductor muscle but negatively linked to digestive gland wet mass. Swimming behavior was mainly related to activity of glycolytic enzymes, and enzymatic activities were related to anatomic parameters. Scallop behavior and physiology change with size, both within our samples and on a larger scale. Small scallops showed more intense swimming activity and had higher arginine kinase activities but lower glycolytic enzyme activities in their adductor muscle than larger scallops. This corresponds to the ontogenetic change in susceptibility to predation and in habitat use observed in C. islandica.     

Larval carry‐over effects from ocean acidification persist in the natural environment

An extensive body of work suggests that altered marine carbonate chemistry can negatively influence marine invertebrates, but few studies have examined how effects are moderated and persist in the natural environment. A particularly important question is whether impacts initiated in early life might be exacerbated or attenuated over time in the presence or absence of other stressors in the field. We reared Olympia oyster (Ostrea lurida) larvae in laboratory cultures under control and elevated seawater pCO₂ concentrations, quantified settlement success and size at metamorphosis, then outplanted juveniles to Tomales Bay, California, in the mid intertidal zone where emersion and temperature stress were higher, and in the low intertidal zone where conditions were more benign. We tracked survival and growth of outplanted juveniles for 4 months, halfway to reproductive age. Survival to metamorphosis in the laboratory was strongly affected by larval exposure to elevated pCO₂ conditions. Survival of juvenile outplants was reduced dramatically at mid shore compared to low shore levels regardless of the pCO₂ level that oysters experienced as larvae. However, juveniles that were exposed to elevated pCO₂ as larvae grew less than control individuals, representing a larval carry‐over effect. Although juveniles grew less at mid shore than low shore levels, there was no evidence of an interaction between the larval carry‐over effect and shore level, suggesting little modulation of acidification impacts by emersion or temperature stress. Importantly, the carry‐over effects of larval exposure to ocean acidification remained unabated 4 months later with no evidence of compensatory growth, even under benign conditions. This latter result points to the potential for extended consequences of brief exposures to altered seawater chemistry with potential consequences for population dynamics.     

Ultrastructure of the mushroom body: digestion during metamorphosis of Utterbackia imbecillis (Bivalvia: Unionidae)

Abstract. Larvae of the freshwater mussel Utterbackia imbecillis metamorphose to juveniles either during their attachment to a host fish, or in vitro in a culture medium. This transformation includes degeneration of larval structures and development of the juvenile morphology. Early in metamorphosis the cells comprising the larval mantle enlarge and project into the mantle cavity, forming a structure referred to as the mushroom body. Its cells, which are ultrastructurally very similar to digestive cells of adult bivalves, are involved in pinocytosis or phagocytosis of the larval adductor muscle and of tissue from the host fish that is enclosed between the larval shells. Ingested material is passed from pinosomes to heterophagosomes which in turn fuse with heterolysosomes, where final degradation of ingested material occurs. Acid phosphatase activity was detected in heterophagosomes and heterolysosomes of all animals examined. In larvae that metamorphosed in vitro , the apical cytoplasm of the cells of the mushroom body, and the extracellular spaces among them, also exhibited acid phosphatase activity. Larvae reared on a host fish accumulated substantial deposits of lipids and glycogen within larval mantle cells during metamorphosis, whereas larvae reared in vitro did not. The larval mantle cells which constitute the mushroom body appear to be the primary sites of intracellular digestion of the larval adductor muscle and host tissue during metamorphosis.     

Heterochrony in Growth and Development in Anurans from the Chaco of South America

Heterochrony refers to those permutations in timing of differentiation events, and those changes in rates of growth and development through which morphological changes and novelties originate during phyletic evolution. This research analyzes morphological variation during the ontogeny of 18 different anuran species that inhabit semi-arid environments of the Chaco in South America. I use field data, collection samples, and anatomical methods to compare larval growth, and sequences of ontogenetic events. Most species present a similar pattern of larval development, with a size at metamorphosis related to the duration of larval period, and disappearance and transformations of larval features that occur in a short period between forelimb emergence and tail loss. Among these 18 species, Pseudis paradoxa has giant tadpole and long larval development that are the results of deviations of rates of growth. In this species events of differentiation that usually occur at postmetamorphic stages have an offset when tail is still present. Tadpoles of Lepidobatrachus spp. reach large sizes at metamorphosis by accelerate developmental rates and exhibit an early onset of metamorphic features. The uniqueness of the ontogeny of Lepidobatrachus indicates that evolution of anuran larval development may occasionally involve mid-metamorphic morphologies conserving a free feeding tadpole and reduction of the morphological-ecological differences between tadpoles and adults.     

The ontogeny of contractile performance and metabolic capacity in a high-frequency muscle

High-performance muscles such as the shaker muscles in the tails of western diamond-backed rattlesnakes (Crotalus atrox) are excellent systems for studying the relationship between contractile performance and metabolic capacity. We observed that shaker muscle contraction frequency increases dramatically with growth in small individuals but then declines gradually in large individuals. We tested whether metabolic capacity changed with performance, using shaker muscle contraction frequency as an indicator of performance and maximal activities of citrate synthase and lactate dehydrogenase as indicators of aerobic and anaerobic capacities, respectively. Contraction frequency increased 20-fold in 20-100-g individuals but then declined by approximately 30% in individuals approaching 1,000 g. Mass-independent aerobic capacity was positively correlated with contractile performance, whereas mass-independent anaerobic capacity was slightly but negatively correlated with performance; body mass was not correlated with performance. Rattle mass increased faster than the ability to generate force. Early in ontogeny, shaker muscle performance appears to be limited by aerobic capacity, but later performance becomes limited equally by aerobic capacity and the mechanical constraint of moving a larger mass without proportionally thicker muscles. This high-performance muscle appears to shift during ontogeny from a metabolic constraint to combined metabolic and mechanical constraints.     

Thermal acclimation,mitochondrial capacities and organ metabolic profiles in a reptile (<Emphasis Type="Italic">Alligator mississippiensis</Emphasis>)

Reptiles thermoregulate behaviourally, but change their preferred temperature and the optimal temperature for performance seasonally. We evaluated whether the digestive and locomotor systems of the alligator show parallel metabolic adjustments during thermal acclimation. To this end, we allowed juvenile alligators to grow under thermal conditions typical of winter and summer, providing them with seasonally appropriate basking opportunities. Although mean body temperatures of alligators in these groups differed by approximately 10°C, their growth and final anatomic status was equivalent. While hepatic mitochondria isolated from cold-acclimated alligators had higher oxidative capacities at 30°C than those from warm-acclimated alligators, the capacities did not differ at 20°C. Cold acclimation decreased maximal oxidative capacities of muscle mitochondria. For mitochondria from both organs and acclimation groups, palmitate increased oligomycin-inhibited respiration. GDP addition reduced palmitate-uncoupled rates more in liver mitochondria from warm- than cold-acclimated alligators. In muscle mitochondria, carboxyatractyloside significantly reduced palmitate-uncoupled rates. This effect was not changed by thermal acclimation. The aerobic capacity of liver, skeletal muscle and duodenum, as estimated by activities of cytochrome c oxidase (COX), increased with cold acclimation. At acclimation temperatures, the activities of COX and citrate synthase (CS) in these organs were equivalent. By measuring COX and CS in isolated mitochondria and tissue extracts, we estimated that cold acclimation did not change the mitochondrial content in liver, but increased that of muscle. The thermal compensation of growth rates and of the aerobic capacity of the locomotor and digestive systems suggests that alligators optimised metabolic processes for the seasonally altered, preferred body temperature. The precision of this compensatory response exceeds that typically shown by aquatic ectotherms whose body temperatures are at the mercy of their habitat.     

Neural retinal regeneration in the anuran amphibian Xenopus laevis post-metamorphosis: transdifferentiation of retinal pigmented epithelium regenerates the neural retina

In urodele amphibians like the newt, complete retina and lens regeneration occurs throughout their lives. In contrast, anuran amphibians retain this capacity only in the larval stage and quickly lose it during metamorphosis. It is believed that they are unable to regenerate these tissues after metamorphosis. However, contrary to this generally accepted notion, here we report that both the neural retina (NR) and lens regenerate following the surgical removal of these tissues in the anuran amphibian, Xenopus laevis, even in the mature animal. The NR regenerated both from the retinal pigment epithelial (RPE) cells by transdifferentiation and from the stem cells in the ciliary marginal zone (CMZ) by differentiation. In the early stage of NR regeneration (5-10 days post operation), RPE cells appeared to delaminate from the RPE layer and adhere to the remaining retinal vascular membrane. Thereafter, they underwent transdifferentiation to regenerate the NR layer. An in vitro culture study also revealed that RPE cells differentiated into neurons and that this was accelerated by the presence of FGF-2 and IGF-1. The source of the regenerating lens appeared to be remaining lens epithelium, suggesting that this is a kind of repair process rather than regeneration. Thus, we show for the first time that anuran amphibians retain the capacity for retinal regeneration after metamorphosis, similarly to urodeles, but that the mode of regeneration differs between the two orders. Our study provides a new tool for the molecular analysis of regulatory mechanisms involved in retinal and lens regeneration by providing an alternative animal model to the newt, the only other experimental model.     

Cellular features of an apoptotic form of programmed cell death during the development of the ascidian, Boltenia villosa

The phylogenetic position of ascidians near the base of the chordate tree makes them ideal organisms for evolutionary developmental studies of programmed cell death (PCD). In the present study, the following key features of an apoptotic form of PCD are described in Boltenia villosa: fragmentation of DNA, increases in plasma membrane permeability, decreases in mitochondrial activity, production of reactive oxygen species (ROS), and caspase activation. First, evidence is presented for apoptosis of cells within the ovary. Later in development, during the early phase of larval tail resorption at the beginning of metamorphosis, some notochord nuclei showed DNA fragmentation and their cell corpses were rapidly eliminated from the larval body. In striking contrast to the rapid demise of notochord cells, larval muscle cells persisted for more than a week within developing juveniles. Rhodamine 123 and MTT experiments suggest that mitochondria within some of the resorbed larval tail muscle cells were metabolically active for more than a week. Furthermore, resorbed tail muscle cells contained a muscle-specific intermediate filament, termed p58, despite relatively high levels of ROS activity and the ubiquitination of their plasma membranes at day two. Corpses of larval tail muscle cells containing aggregated pigment granules survived within juveniles for more than a month, in contrast to the rapid elimination of notochord cells. Evidence consistent with the formation of larval muscle cell apoptotic bodies is presented. The most surprising result of the present study was that caspase-8, usually associated with apoptotic signaling, was activated in larval endoderm cells that develop into adult structures. When the present results were compared to features of PCD previously reported in other ascidians, significant species differences in PCD were revealed.     

Social facilitation is a better predictor of frog reproductive activity than environmental factors

Anuran breeding activity is frequently linked to environmental factors, mainly temperature and rainfall. However, a key feature of anuran reproductive behavior—gathering in choruses and producing loud advertisement calls to attract females—generates a conspicuous social cue that may also facilitate reproductive behavior. Here, I examine the relative importance of environmental and social factors in explaining the intensity of reproductive activity in the Neotropical treefrog Hypsiboas rosenbergi. I show that social cues generally play an important role, but that there are sex differences: male behavior is associated with a combination of environmental and social factors, while female behavior is associated almost exclusively with social cues. I discuss the potential benefits of using social cues in regulating breeding activity, and suggest that conservation efforts may take advantage of the apparently widespread pattern of social facilitation in anuran reproductive ecology.     

Effects of conditionally expressed phenotypes and environment on amphibian dispersal in nature

Individuals vary greatly in the distance they disperse, and in doing so, strongly affect ecological and evolutionary processes. Dispersal, when viewed as a component of phenotype, can be affected independently or jointly by environment. However, among taxa with complex life cycles that occupy different habitats over ontogeny, the effects of environment on dispersal and the interaction between environment and phenotype remains poorly understood. Here, we conducted a field experiment to measure how dispersal distance was affected by phenotype, environment experienced before and after metamorphosis, and their interaction. We manipulated the environment encountered by a pond‐breeding salamander Ambystoma annulatum during the aquatic larval stage and again as dispersing terrestrial juveniles. After assaying juvenile phenotype (exploration behavior, body condition, and morphology), we then measured the initial distance dispersed by juveniles. The distance moved by dispersing salamanders was affected by attributes of both larval and juvenile habitat, with salamanders that encountered low quality habitat in either life stage moving the farthest. However, we did not find support for an interactive effect of phenotype and environment affecting the distance moved by dispersers. Interestingly, exploration behavior explained the distance moved by philopatric animals but not dispersing ones. Our findings indicate that the environment experienced before metamorphosis can affect juvenile dispersal behavior, and demonstrates the need to consider dispersal in species with complex life cycles to understand the coupling between local and regional population dynamics.     

Ontogenetic changes in enzyme activities associated with energy production in the spiny lobster, Jasus edwardsii

The larval life of the spiny lobster Jasus edwardsii is one of the longest and most complex of any marine organism and is poorly understood due to the difficulty of studying cryptic, pelagic organisms. Hence, the capacity for active swimming in the phyllosoma, puerulus and juvenile stages and the use of possible metabolic fuel reserves was inferred from a number of enzyme activities, including citrate synthase, lactate dehydrogenase, and HOAD. High activities of CS and LDH in abdominal tissues of Stage 11 phyllosoma and pueruli are consistent with a capacity to commence active on-shore movement. The activities of LDH and HOAD showed positive allometry while CS was independent of body mass. The body mass dependence of LDH activity may reflect the developing ability of the lobster to initiate brief escape manoeuvres, and the scaling of HOAD reflects an increased use of lipid fuel reserves. Aerobic enzyme activities were higher in abdominal tissues than in cephalic tissues of pelagic pueruli, but high activities appear in the cephalic tissues of juveniles. These changes mirror a developmental shift in activity from pelagic oceanic swimming to a benthic existence on the seabed of the near shore. The low LDH activity in pueruli confirmed previous findings that they have limited feeding capacity, with carbohydrate contributing little towards the major energy reserves. The highest LDH activities occur in the abdominal muscles of juveniles and correlate with rapid tail-flicking escape behaviour. The activities of HOAD increased throughout development, and in the abdominal tissues of juveniles, may reflect lipid transformation and accumulation as an energy reserve. Enzyme activities, therefore, provide useful information concerning migratory behaviour that is presently unavailable from ecological studies.     

Characterization and expression of calmodulin gene during larval settlement and metamorphosis of the polychaete Hydroides elegans

The polychaete Hydroides elegans (Serpulidae, Lophotrochozoa) is a problematic marine fouling organism in most tropical and subtropical coastal environment. Competent larvae of H. elegans undergo the transition from the swimming larval stage to the sessile juvenile stage with substantial morphological, physiological, and behavior changes. This transition is often referred to as larval settlement and metamorphosis. In this study, we examined the possible involvement of calmodulin (CaM) - a multifunctional calcium metabolism regulator, in the larval settlement and metamorphosis of H. elegans. A full-length CaM cDNA was successfully cloned from H. elegans (He-CaM) and it contained an open reading frame of 450 bp, encoding 149 amino acid residues. It was highly expressed in 12h post-metamorphic juveniles, and remained high in adults. In situ hybridization conducted in competent larvae and juveniles revealed that He-CaM gene was continuously expressed in the putative growth zones, branchial rudiments, and collar region, suggesting that He-CaM might be involved in tissue differentiation and development. Our subsequent bioassay revealed that the CaM inhibitor W7 could effectively inhibit larval settlement and metamorphosis, and cause some morphological defects of unsettled larvae. In conclusion, our results revealed that CaM has important functions in the larval settlement and metamorphosis of H. elegans.     

The evolution of lamprey (Petromyzontida) life history and the origin of metamorphosis

Modern lampreys (Petromyzontiformes) are one of two lineages of surviving jawless fishes (agnathans), and are thus of critical importance to understanding the evolution of the vertebrates. Although their fossil record is meager, it appears they have remained morphologically conserved for at least 360 million years, but the origin of their multi-stage life history is unclear. Unlike hagfishes, the other extant group of jawless fishes, which exhibit direct development, all modern lampreys possess a complex life cycle which includes a long-lived freshwater larval (or ammocoete) period, followed by a true metamorphosis into a sexually-immature juvenile and then mature adult which differ dramatically in their morphology and ecology from the larva. Because of their basal position, it is critical to understand when the extant lamprey life history evolved, and if such a life history was present in the last common ancestor of agnathans and gnathostomes. Recent discoveries in paleontology, genomic analyses, and developmental biology are providing insights into this problem. The current review synthesizes these findings and concludes that the ancestral lamprey life cycle followed a direct development. We suggest that the larval period was short and relatively limited if present at all, but that the juvenile included modern larval traits; over the course of evolution, differential selection pressures throughout the lifetime produced distinct larval and juvenile/adult periods. Each period required the dramatically different morphologies seen in modern lampreys, ultimately requiring a true metamorphosis to accommodate the large changes in the body plan and to maximize the efficiency of each life period. As a result, modern lamprey life histories are a patchwork of ancestral and derived characters.     

An association of melanophores appearing at metamorphosis as vehicles of asymmetric skin color formation with pigment anomalies developed under hatchery conditions in the Japanese flounder, Paralichthys olivaceus

The mechanisms for asymmetric skin color formation in the Japanese flounder are studied with particular concerns to causes for pigment disorder (hypomelanosis) occurring under hatchery conditions. For an analysis of normal pigmentation, fish were raised with wild zooplanktons in an indoor hatchery, whilst for hypomelanosis, they were raised with Brazilian Artemia nauplii, a diet used in the hatcheries. Morphological observations, counting of melanophores, histochemical assay of DOPA-positive immature cells (melanoblasts), and radiometric estimation of tyrosinase activities in skins of developing larvae and juveniles indicate that 1) the structural plan for pigmentation in this species is bilaterally symmetric until metamorphosis, utilizing large-sized melanophores (hence larval melanophores) as main vehicles, and 2) an asymmetric coloration characteristic to metamorphosed juveniles is formed by an intensive development of smaller-sized melanophores (hence adult-type melanophores) appearing selectively in the ocular side at the later stages of metamorphosis and by an absence of it in the blind. These findings apparently indicate that 1) two types of melanophores occur in this species which differ with respect to morphological properties and developmental fate, and 2) selective differentiation of adult type melanophores in the ocular side of the body at or after metamorphosis is primarily responsible for an asymmetric coloration of its adult form. The similar assays on the fish fed with Artemia nauplii indicate that defective development of adult-type melanophores results in hypomelanosis in their ocular-sided skins, yielding a pigmentary pattern seen in the blind side of the metamorphosed juveniles with normal pigmentation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic correlates of burst swimming capacity of juvenile and adult threespine stickleback (Gasterosteus aculeatus)

The relationship between burst swimming performance and muscle metabolic capacities was examined in juvenile and adult threespine sticklebacks (Gasterosteus aculeatus). The absolute burst speed measured during startle responses increased markedly with growth of juveniles, but this positive allometry did not continue in adults. The allometry of phosphofructokinase (PFK), lactate dehydrogenase, creatine phosphokinase activities and protein concentrations was positive in juveniles and became negative in adults. The lower activities in adults may reflect the mobilization of muscle proteins for reproduction. In juveniles, absolute burst swimming and muscle glycolytic capacity show a similar allometry. However, when the influence of factors such as size and age was removed by calculating residuals from multiple regressions, variation in muscle enzyme activities in juveniles did not explain variation in their swimming capacity. In adults, interindividual variation in PFK and cytochrome C oxidase activities was correlated with variation in the burst swimming capacity. Apparently, mobilization of muscle proteins in support of reproduction may lead muscle enzyme levels to limit burst performance. Accepted: 9 November 1998