Timing Of Metamorphosis Research Articles

Relationship of Pond Drying to the Reproductive Success of the Salamander Ambystoma talpoideum

The relationship of pond drying, female population size, and total egg production to the reproductive success (number of metamorphosing juveniles) of the salamRnder Ambystoma talpoideum was studied in natural and experimental populations. Breeding population size was correlated with rainfall during the migratory season but not with the production of juveniles in the previous year. Reproductive success and survival to metamorphosis were correlated with the number of days in a year that a pond had standing water but not with the number of breeding females or total number of eggs oviposited. The time of metamorphosis was correlated with the date that the pond dried. However, metamorphosing later in the season did not result in larger body size at metamorphosis, only more mptamorphs. Catastrophic mortality occurred when breeding ponds dried early, resulting from the failure of larvae to reach a threshold size or developmental stage to initiate metamorphosis. Manipulation of an experimental pond suggested that growth rate of larvae decreased as the pond dried. Desiccation was identified as a factor influencing the fluctuations in reproductive success of a species breeding in temporary ponds. .

NOREPINEPHRINE AND DOPAMINE CONTENT OF LARVAE AND SPAT OF THE PACIFIC OYSTER, CRASSOSTREA GIGAS.

Oyster larvae and spat of varying ages were homogenized and analyzed for catecholamine content using high-performance liquid chromatography with electrochemical detection. Norepinephrine (NE) and dopamine (DA) were found in appreciable quantities, with more DA present than NE. The presence of epinephrine was equivocal. Norepinephrine levels were low in young larvae (0.062 ± 0.035 pg/µg protein), then increased to an intermediate level (0.517 ± 0.031 pg/µg protein) for most of the larval period and finally increased again just before metamorphosis to 1.08 ± 0.09 pg/µg protein. Dopamine levels in the corresponding larval groups did not change significantly, with 11.5 ± 1.9, 8.58 ± 0.98, and 7.47 ± 0.92 pg DA/µ protein, respectively. The levels of NE (1.00 ± 0.04 pg/µg protein) and DA (7.13 ± 0.29 pg/µg protein) present in spat following metamorphosis were not significantly different from the pre-metamorphic values. The presence of NE in oyster larvae at the time of metamorphosis supports the hypothesis of a role for endogenous NE in mediating metamorphosis.

The effects of temperature and food on naupliar development, growth and metamorphosis in three species of Boeckella (Copepoda:Calanoida)

Three species of Boeckella (B. triarticulata, B. dilatata and B. hamata) were reared from hatching to copepodite I (CI) at three naturally fluctuating food levels and three temperatures in a 3 × 3 × 3 factorial design. Development times, lengths and mortality were measured for each species in nine treatments. Temperature had the major effect on development times but food level had the major effect on CI lengths. Mortality varied interspecifically with treatment. The combined effect of temperature and food on development times and lengths was species-specific. There were trade-offs between development time and growth to meet constraints imposed by naupliar metamorphosis. The three species varied in the timing of metamorphosis to CI. B. triarticulata nauplii were age determined, B. dilatata nauplii were size determined and B. hamata nauplii were flexibly age and size determined depending on treatment. Differences in life history parameters and the timing of naupliar metamorphosis are discussed in relation to the distributions of the species in ponds (B. triarticulata), glacial lakes (B. dilatata) and coastal lakes (B. hamata) in the South Island of New Zealand.

Hormonal regulation of sequential larval cuticular gene expression

As the tobacco hornworm (Manduca sexta) larva feeds and grows, the abdominal epidermis synthesizes larval endocuticular proteins. During a molt this synthesis temporarily ceases while the cells deposit a new epicuticle; then these proteins reappear in a sequential manner, some before ecdysis, others after ecdysis. At the time of metamorphosis, the epidermis becomes pupally committed and ceases synthesizing these endocuticular proteins. Northern and dot blot hybridization analysis using cDNA clones for three different low-molecular-weight larval cuticular proteins showed that RNA transcription of all three ceased by the time of head cap slippage during the molt, then begins again just before ecdysis, one showing a different time course from the other two. All responded to the commitment peak of ecdysteroid in the absence of juvenile hormone (JH) by a permanent cessation of transcription. During the final day of feeding (day 3) of the 5th instar the cuticular lamellae become 5–10 times thinner coincidentally with a change in cuticular protein synthesis involving a cessation of synthesis of many of the endocuticular proteins and the appearance of at least three new proteins — 14.5, 15, and 27 kd (kilodaltons). Incubation of day 15th instar epidermis with 10–100 ng/ml 20-hydroxyecdysone (20HE) induced the synthesis of the 27-kd protein and the transcription of the mRNAs for the 14.5- and 15-kd proteins. Incubation in the absence of hormones or with 20HE in the presence of JH prevented the appearance of these new proteins and the deposition of thin lamellae. The mRNAs for three endocuticular proteins whose synthesis ceases on day 3 showed differing responses to 20HE and JH. Thus, the sequential program of larval endocuticular gene expression is controlled primarily by hormonal titers in both the molt and the intermolt periods.

Immunocytochemical Localization and Immunological Characterization of Vitamin D-Dependent Calcium-Binding Protein in the Bullfrog Cerebellum

Antiserum prepared against rat renal calcium-binding protein (CaBP) was used with the unlabeled antibody peroxidase-antiperoxidase (PAP) technique to localize the 28,000 molecular weight CaBP in the cerebellum of the bullfrog, Rana catesbeiana. Whole brains of premetamorphic tadpoles and adults were fixed in Bouin's solution for 2 or 24 h and embedded in paraffin. 8-microns parasagittal sections were prepared and treated by the PAP method. Purkinje cells of the cerebellum in tadpoles and adults were specifically stained for CaBP. In the premetamorphic corpus cerebelli, the stained Purkinje cells corresponded to the precociously developed Purkinje cells described previously. In the auricular lobe region of the cerebellum mature Purkinje cells were stained. In addition, smaller stained cells were seen. The latter were presumed to be immature Purkinje cells that would mature at the time of metamorphosis. Immunoblot procedure demonstrated cross-reactivity for the ranid brains in the 28,000 molecular weight region. This immunoreactive band comigrated with the immunoreactive band observed with purified rat renal CaBP. Although the exact functional significance of CaBP is unknown at this time, our immunocytochemical and immunological findings indicate that CaBP is an excellent marker for studies of Purkinje cell maturation.

Growth of the Mountain Brook Lamprey Ichthyomyzon greeleyi Hubbs and Trautman

Larvae, metamorphosing stages and adults of Ichthyomyzon greeleyi, a nonparasitic lamprey, were collected from four streams tributary to the French Broad River in western North Carolina to provide information on seasonal rates of growth, duration of the larval period, timing of metamorphosis and changes in body proportions. Metamorphosis is initiated in mid-Aug. and completed by mid-Dec. The larval period ranges between 5.2-6.2 yr with the oldest individuals being predominately female. Larval growth was most rapid during the spring and summer. Negative growth occurred during the winter among the older age groups. Annual growth increased asymptotically and was similar among three of the four populations. Differences in growth were not demonstrable between male and female larvae. A preponderance of females occurred among larvae with males being the more abundant among metamorphosing animals and adults. The change in sex ratio is attributable to the longer larval life of females. The proportional length of the prebranchial, branchial, trunk and tail regions changed throughout larval life in a pattern similar to that for other lampreys. Oral disc, dorsal-fin height and eye diameter increased through all or most of metamorphosis and the adult period.

Predicting Anuran Metamorphosis and Energetics

Rates of growth (Pr) and metabolism (Mr) as well as timing of metamorphosis can be precisely described using feeding rate (Cr) as the predictor in Rana tigrina and selected anurans exposed to variables of more than one environmental factor. To predict size at metamorphosis in these anurans, Pr and development rate (Dr) as well as stage-specific growth (Ps) are jointly used as the predictor. Since Cr can predict Pr and Dr, one must know Cr and Ps to predict size at metamorphosis when variables of more than one environmental factor are considered.

Time and Energy Costs of Metamorphosis in the Indian Bullfrog Rana tigrina

Ran tigirina tadpoles were reared on different foods and rations at diffrent temperatures and larval densities in waters of diffrent qualities and at different aquarium water depths. Time and energy costs of metamorphosis were estimated. With the exception of temperature, none of these factors affect the duration of the metamorphic period, although they influence larval duration. They affects energy density of the frog at the initiation and termination of metamorphosis. Ration, larval density and food quality alter the energy density of the tadpole at climax. The metamorphic events results in loss of tadpole energy and depletion of energy density. Accumulation of 1,500 J by the terminal tadpole is the minimum required energy for successful metamorphosis. A greater accumulation of body (size) energy in the terminal tadminal tadpole is advantageous, as it enhances metamorphic efficiency and reduces metamorphic metabolic rate. High metabolic rate during the larval period is associated with low metabolic rate during the metamorphic period. Metamorphic metabolic rate and energy content of the freshly emerged froglet can be predicted from that of the terminal larva.

Plasticity in the Fine Timing of Metamorphosis in Tadpoles of the Hylid Frog, Litoria ewingi

LIGHT, L. E. 1974. Survival of embryos, tadpoles, and adults of the frogs Rana aurora aurora and Rana pretiosa pretiosa sympatric in southwestern British Columbia. Can.J. Zool. 52:613-627. MILLER, N. 1909. The american toad (Bufo lentiginosus americanus, LeConte) II. A study in dynamic biology. Amer. Nat. 18:730-745. MOORE,J. A. 1939. Temperature tolerance and rates of development in the eggs of amphibians. Ecology 20:459-478.

Anuran Size at Metamorphosis: Experimental Test of a Model Based on Intraspecific Competition

Size at metamorphosis and length of larval period are often, but not invariably, correlated within cohorts of larval anurans. Collins (1979) proposed intraspecific competition as one causative agent for such a correlation in nature, and this hypothesis was supported by observational data. This study reports the results of an experimental test of that hypothesis. Isolated larvae were reared at one of two food levels (high or low) and, during the period in which metamorphosis occurred, were maintained at either constant per capita food levels, or at increasing per capita levels designed to mimic effects of continual release from scramble—type, exploitative competition. Low food levels decreased average larval growth and average size at metamorphosis and increased average length of larval period. A reduced level of food had no effect on the relative variation in length of larval period. Only competitive release affected the relative variation in size at metamorphosis. All four treatments displayed a positive correlation between size at metamorphosis and length of larval period, but only in the combination of low food levels and competitive release was the correlation more than barely significant. Size at metamorphosis displayed a positive allometric relationship to length of larval period in the low food—release treatment, and a negative allometric relationship in the other three treatments. These results support Collins' (1979) model for intraspecific competition as one causative mechanism for such relationships. Certain aspects of these results support each of two distinct models for the timing of amphibian metamorphosis, but the data as a whole do not fit well with either model.

An anatomical and electrophysiological study of synapse elimination at the developing frog neuromuscular junction

Synapse elimination was examined in the developing frog cutaneous pectoris muscle using histological and electrophysiological techniques. Morphological synapse elimination occurred in two phases. The first phase, which began at the time of metamorphosis and continued until the second to third postmetamorphic week, was characterized by a rapid decline in the number of endplates receiving ⩾3 synaptic inputs. However, 50% of the muscle fibers still remained dually innervated. This dual innervation decreased with a much slower time course; approximately 20% of the muscle fibers were dually innervated in 1- to 2-year-old frogs. During the first phase of synapse elimination no difference was noted between the distribution of acetylcholine receptors or acetylcholinesterase activity associated with the terminal arborizations formed by separate axons at one synaptic site. However, terminal arborizations formed by small diameter axons and consisting of varicosities separated by thin interconnectives became apparent during this period. Such varicose arborizations responded to nerve stimulation and released acetylcholine in proportion to their terminal length as did the nonvaricose arborizations. In addition, the number of morphological and physiological inputs at one endplate site was well correlated throughout the first phase of synapse elimination.

Soldier determination in Pheidole bicarinata: Effect of methoprene on caste and size within castes

Topical application of methoprene to final-instar larvae of the ant Pheidole bicarinata can induce soldier development. Soldier induction takes place if methoprene levels are above a soldier-determining threshold during a critical period of juvenile hormone-sensitivity that occurs during about days 4–6 of the final instar. Furthermore, the amount of exogenous methoprene applied affects the timing of metamorphosis and the adult size in both the minor worker and soldier castes. When larvae that receive methoprene treatment become minor workers these are always larger than acetone-treated controls. In larvae that become soldiers, growth and timing of metamorphosis vary with the dose of methoprene, but in a more complex way. A high dose of methoprene produces a metamorphic delay and large soldiers. However, the lowest effective dose for soldier induction produces early metamorphosis and small adults. On the basis of these results, we have expanded our model of a mechanism by which juvenile hormone could control determination of worker castes in Pheidole bicarinata.

Food and feeding habits of Triturus vulgaris (L.) and T. cristatus (LAURENTI) (Amphibia) in two bog tarns in central Norway

AbstractThe diets oftwo sympatric species of newts, Triturus vulgaris(L.) and T. cristatus(LAURENTI), from two localities in central Norway, have been compared. Adult T. vulgaris ate mainly those Cladocera which can be classified as planktonic, and to a lesser degree those which are predominantly benthic. The food of T. cristatus was predominantly benthic invertebrates and Cladocera associated with the bottom. T. vulgaris larvae ate planktonic - and predominantly benthic Cladocera, and to a certain degree also larger benthic invertebrates, while T. cristatus larvae (July-August) had taken almost exclusively Cladocera, 75% of which can be classified as planktonic. Large T. cristatus larvae (in September) had eaten relatively more benthic prey. These data would fit the hypothesis that the modes of feeding of the species are different: Adult T. vulgaris swim about in the water much of the time, while T. cristatus stay on the bottom. Among the young, T. vulgaris larvae are mainly associated with the bottom, while T. cristatus larvae are definitely more nektonic during most of the summer; large T. cristatus larvae, however, when nearing the time for metamorphosis, become benthic.

Particle exclusion by discoidal reticulate lamellae in larval gastropod feeding structures

The feeding apparatus of larval gastropods includes fibrous, meshlike structures connecting the bases of adjacent cilia and microvilli. These multilayered structures, termed discoidal reticulate lamellae, are found only in the velar food groove, mouth, esophagus, and part of the anterior alimentary canal of larval gastropods. They first appear during the early veliger stage and may be secreted by epidermal gland cells. Discoidal reticulate lamellae exist throughout larval life and are lost at the time of metamorphosis. They do not occur in adult gastropods, in larvae or adults of nongastropod molluses, or in the larvae of at least seven nonmolluscan invertebrate phyla. Discoidal reticulate lamellae apparently function to exclude ultramicroparticles from epithelial crypts. Studies with particulate tracers (colloidal gold, ferritin, ruthenium red) demonstrate that particles greater than approximately 60 nm in diameter are totally excluded by the lamellae, whereas particles down to approximately 20 nm in diameter are usually excluded.

Anomalous anatomy of identified neurons in the larval prawn: spontaneous and induced by microlesions

The abdominal ganglia of the prawn Macrobrachium rosenbergii undergo developmental changes of fundamental interest between the time of hatching and metamorphosis. These changes include an increase in cell numbers and changes in the connectivity between identified neurons. The giant motoneurons involved in the escape response, which form a syncytium in the adult, are observed as separate neurons with crossed axons in early larvae. Anomalous growth and connections of identified neurons were studied in order to gain some understanding of the rules and mechanisms governing normal development. Spontaneous anomalies included: supernumerary axons and abnormal axonal trajectories. The plasticity and specificity of identified neurons were studied by following the anatomical effects of deletions of giant neurons. Microlesions were inflicted reproducibly by means of a focused beam of visible and ultraviolet light. Within a day, irradiated cell bodies are eliminated; complete disappearance of the axon takes about 10 days, indicating that the remarkable ability of some invertebrate neurons to survive without a soma is not present in the larval prawn. As a result of the removal of an axon, the most common effect found in central connections was the absence of the collaterals or axons deprived of their targets. No collateral sprouting was detected in the central nervous system. In about a third of the ganglia where a giant motoneuron was killed and structure was analyzed 2 or more weeks after irradiation, anomalous connections were found. They usually involved contacts between an interneuron deprived of its normal target and the contralateral motoneuron which remained intact. The restricted types of anomalies observed support the notion of a hierarchical order in the rules governing formation of central synapses, in which neuron type ranks higher than laterality.

Soldier Determination in Ants: New Role for Juvenile Hormone

Topical application of juvenile hormone analog induces soldier development in the ant Pheidole bicarinata. Soldier induction takes place if the juvenile hormone analog is present during a period of sensitivity that occurs during the last larval instar. Control of worker dimorphism seems to be accomplished through control of timing of metamorphosis. The smallest size at which metamorphosis can be initiated is shifted upwardfrom 1.2 to 1.7 millimeters by exposure to the juvenile hormone analog during the sensitive period.

Energy accumulation and amphibian metamorphosis.

Timing of metamorphosis and size at metamorphosis were examined for Hyla crucifer under two densities in the laboratory. Results agree with previously known relationships for ranids and bufonids: at higher densities developmental time is longer, mean size at metamorphosis is smaller, and both parameters have greater variance than at lower densities. Density also affects energy accumulation: under ad libitum feeding conditions, an average individual raised at a higher density is able to accumulate less energy before metamorphosis than an average individual raised at a lower density. The suggestion is made that, in addition to growth and differentiation rates, energy accumulation may be important in determining when amphibian metamorphosis occurs.

Selected Aspects of the Larval Ecology of the Marbled Salamander Ambystoma opacum in the Southern Portion of Its Range

Selected aspects of the larval ecology of Ambystoma opacum were studied from 1977-1979 in S-central Alabama. Differences were found in the length of the larval period, time of metamorphosis, stratification behavior and feeding patterns of larvae when compared to other populations. Substantial differences in hatching dates and growth periods occurred between local pools. In addition, estimated differences in hatching dates of as much as 2 months occurred within one pool that filled incrementally. In general, the larval period was shorter, the time of metamorphosis earlier, and the size at metamorphosis smaller than those of northern populations. Larval growth was relatively slow during the 1st 6 weeks after hatching, but accelerated during the remainder of the larval stage. Increases in weight were proportionately greater than increases in body length during the last 6 weeks of growth. Copepods, cladocerans, ostracods, isopods and amphipods were important food items of larvae. Strong shifts to alternate food items did not occur as larvae grew. Instead, larvae maintained a generalist feeding habit throughout their development. Larvae fed continuously throughout the day and did not limit their feeding to the stratification period. The diurnal aggregation of larvae on pool bottoms and their upward movements at night often corresponded to similar movements of macrozooplankton. Stratification was not strongly associated with changes in physical factors other than light and was observed in all size classes of larvae except those nearing metamorphosis.

Variation in serum levels of thyroxine in anadromous larval lampreys, Petromyzon marinus L

Circulating levels of thyroxine in samples of fresh sera taken from larval anadromous sea lampreys ( Petromyzon marinus L.) were measured by means of radioimmunoassay. Average sera thyroxine levels varied from a minimum of 4.92 μg/100 ml in March to a high of 18.49 μg/100 ml in June. Variations are discussed in relation to temperature, metabolic state of the animal, and the time of metamorphosis.

Active Suppression of the Allogeneic Histocompatibility Reactions During the Metamorphosis of the Clawed Toad Xenopus

Metamorphosis is a privileged period for the induction of tolerance to allografts. Transfer of lymphocytes from metamorphosing Xenopus into isogenic adults prevented the rejection of a skin graft differing from the adult host by minor histocompatibility antigens. This implies that active suppression is involved at one step of the induction of tolerance to the self-antigens that differentiate at the time of metamorphosis. The reciprocal experiments of preventing tolerance induction by transfer of normal adult cells into metamorphosing animals failed. However, passive transfer of anti-graft immunity in tolerant animals was partially observed, provided that a transfer of primed cells was done simultaneously with the challenging graft. Thus, memory cells are not as sensitive to the suppression as are the cells that respond in a first set reaction.