Embryonic learning and developmental carry-over effects in an invasive anuran

Carry-over effects influence trait responses in later life stages as a result of early experience with environmental cues. Predation risk is an influential stressor and selection exists for early recognition of threats. In particular, invasive species may benefit from carry-over effects by preemptively recognizing and responding to novel predators via latent developmental changes and embryonic learning. In a factorial experiment, we conditioned invasive American bullfrog embryos (Lithobates catesbeianus) to the odor of a novel fish predator, largemouth bass (Micropterus salmoides) alone or in combination with injured conspecific cues. We quantified developmental carryover in the larval life stage and found that individuals conditioned to the highest risk (fish and injured conspecific cues) grew into longer bodied larvae relative to larvae from lower risk treatments. We also assessed embryonic learning, a behavioral carry-over effect, and found an interaction between embryonic conditioning and larval exposure. Behavioral responses were only found in scenarios when predation risk varied in intensity across life history stages, thus requiring a more flexible antipredator strategy. This indicates a potential trade-off between the two strategies in larval growth and development rates, and time until metamorphosis. Our results suggest that early predator exposure and carry-over effects have significant impacts on life history trajectories for American bullfrogs. This research contributes to our understanding of a potentially important invasion mechanism in an anuran species of conservation concern.     

The effects of nurse eggs and sibling interactions on the larval development of the poecilogonous annelid Boccardia proboscidea (Spionidae)

In poecilogony, different types of larvae are produced within the same species. Previous studies have suggested maternal control of the production of larval types; however, it is not clear which factors or mechanisms generate contrasting developmental patterns among siblings. The spionid polychaete Boccardia proboscidea produces within the same capsule adelphophagic larvae that eat nurse eggs and siblings and complete all or most of their development inside the capsule (Type A larvae), and larvae with little growth until they hatch as planktotrophic larvae (Type B larvae). In this study, we manipulated capsule content to explore the factors determining larval type in B. proboscidea and the role of extra‐embryonic maternal nutrition and sib–sib interaction in the developmental fate of offspring. When early larval stages were grown individually in vitro, with nurse eggs as the only food source, some of them remained small, while others continue developing into larger pre‐competent larvae by feeding on nurse eggs. This suggests that larval types in B. proboscidea are determined very early in development and are not solely the product of sib–sib interaction inside the capsule. However, our data also suggest that hatching size variability within larval types of a clutch depends on nurse egg availability. Type B larvae grew normally to metamorphosis when phytoplankton was available, but suffered high rates of cannibalism by Type A larvae. These results are consistent with the hypothesis that individual larval fates are determined very early in development and that once their fate is determined, hatching size and intracapsular survival are affected by maternal food provisioning and sibling interaction.     

Ontogenic change in tissue osmolality and developmental sequence of mitochondria-rich cells in Mozambique tilapia developing in freshwater

We investigated a change in tissue fluid osmolality and developmental sequences of mitochondria-rich (MR) cells during embryonic and larval stages of Mozambique tilapia, Oreochromis mossambicus, developing in freshwater. Tissue osmolality, representing body fluid osmolality, ranged from 300 to 370 mOsm/kg during embryonic and larval stages. This suggests that tilapia embryos and larvae are also able to regulate body fluid osmolality to some extent, although the levels are somewhat higher and fluctuate more greatly in embryos and larvae than in adults. Na⁺/K⁺-ATPase-immunoreactive MR cells were first detected in the yolk-sac membrane 3 days before hatching (day − 3), followed by their appearance in the body skin on day − 2. Subsequently, MR cells in both the yolk-sac membrane and body skin increased in number, and most densely observed on days − 1 and 0. Whereas yolk-sac and skin MR cells decreased after hatching, MR cells in turn started developing in the gills after hatching. Thus, the principal site for MR cell distribution shifted from the yolk-sac membrane and body skin during embryonic stages to the gills during larval stages, and tilapia could maintain continuously their ion balance through those MR cells during early life stages.     

Effects of temperature on embryonic and early larval growth and development in the rough-skinned newt (Taricha granulosa)

We investigated the effects of temperature on the growth and development of embryonic and early larval stages of a western North American amphibian, the rough-skinned newt (Taricha granulosa). We assigned newt eggs to different temperatures (7, 14, or 21 °C); after hatching, we re-assigned the newt larvae into the three different temperatures. Over the course of three to four weeks, we measured total length and developmental stage of the larvae. Our results indicated a strong positive relationship over time between temperature and both length and developmental stage. Importantly, individuals assigned to cooler embryonic temperatures did not achieve the larval sizes of individuals from the warmer embryonic treatments, regardless of larval temperature. Our investigation of growth and development at different temperatures demonstrates carry-over effects and provides a more comprehensive understanding of how organisms respond to temperature changes during early development.     

Effects of methylmercury on the morphogenesis of the rat cerebellum

Developing rat cerebellums were examined following continuous methylmercury exposure via maternal drinking water at 12.5 ppm during gestation and the suckling period. The continuous exposure resulted in reductions of the total cerebellar cell population and higher mercury tissue burdens than previous acute-dose studies. Cell necrosis was not evident, but rather alterations in the pattern of mitotic figures were observed. A decreased number of cells in the methylmercury exposed cerebellums was associated with an increased number of mitotic figures in the early stages of mitosis and a decrease in the number in the middle and late stages. These in vivo exposure observations are consistent with in vitro cell cycle studies in which the cells were found to have accumulated in G2 and early M phases. Impaired cell proliferation is suggested to be a major mechanism of developmental neurotoxicity following continuous low-dose exposure to methylmercury.     

Past and Present Risk: Exposure to Predator Chemical Cues Before and after Metamorphosis Influences Juvenile Wood Frog Behavior

Animals are exposed to different predators over their lifespan. This raises the question of whether exposure to predation risk in an early life stage affects the response to predators in subsequent life stages. In this study, we used wood frogs (Rana sylvatica) to test whether exposure to cues indicating predation risk from dragonfly larvae during the wood frog larval stage affected post‐metamorphic activity level and avoidance of garter snake chemical cues. Dragonfly larvae prey upon wood frogs only during the larval stage, whereas garter snakes prey upon wood frogs during both the larval stage and the post‐metamorphic stage. Exposure to predation risk from dragonflies during the larval stage caused post‐metamorphic wood frog juveniles to have greater terrestrial activity than juvenile wood frogs that were not exposed to larval‐stage predation risk from dragonflies. However, exposure to predation risk as larvae did not affect juvenile wood frog responses to chemical cues from garter snakes. Wood frogs exposed as larvae to predation risk from dragonfly larvae avoided garter snake chemical cues to the same extent as wood frog larvae not exposed to predation risk from dragonfly larvae. Our results demonstrate that while some general behaviors exhibit carry‐over effects from earlier life stages, behavioral responses to predators may remain independent of conditions experienced in earlier life stages.     

Lipid peroxidation and antioxidant defence status during larval development and metamorphosis of giant prawn,Macrobrachium rosenbergii

In the present communication we studied the involvement of reactive oxygen species and alteration in antioxidant defence status during larval development and metamorphosis of giant prawn, Macrobrachium rosenbergii. Overall results indicate that there was a decline in endogenous lipid peroxidation level during larval development. Activity of superoxide dismutase was the lowest in early larval stages (Zoea-I and II) and thereafter increased in V and VI stages, followed by a decrease in the subsequent larval stages. Catalase and glutathione peroxidase did not exhibit specific pattern of changes during development. Reduced glutathione content exhibited an incremental increase during larval progression until metamorphosis. Ascorbic acid content of the larval tissue remained unaltered during development but a sharp fall was marked in its content in the post-larvae. Hence it is concluded that early larvae face high oxidative stress as evident from the high content of thiobarbituric acid reactive substances. This may be due to direct exposure of larvae to ambient oxygen of the water as well as their low antioxidant potential. However, during development with the augmentation in antioxidant reserve of the larval tissues a diminution in the oxidative stress was recorded. Thus it is presumed that antioxidant defences play an important role in providing protection to the developing larvae from oxidative assault during larval progression and metamorphosis.     

Accumulation of mercury in estuarine food chains

To understand the accumulation of inorganic mercury and methylmercury at the base of the estuarine food chain, phytoplankton (Thalassiosira weissflogii) uptake and mercury speciation experiments were conducted. Complexation of methylmercury as methylmercury-bisulfide decreased the phytoplankton uptake rate while the uptake rate of the methylmercury-cysteine and -thiourea complexes increased with increasing complexation by these ligands. Furthermore, our results indicated that while different ligands influenced inorganic mercury/methylmercury uptake by phytoplankton cells, the ligand complex had no major influence on either where the mercury was sequestered within the phytoplankton cell nor the assimilation efficiency of the mercury by copepods. The assimilation efficiency of inorganic mercury/methylmercury by copepods and amphipods feeding on algal cells was compared and both organisms assimilated methylmercury much more efficiently; the relative assimilation efficiency of methylmercury to inorganic mercury was 2.0 for copepods and 2.8 for amphipods. The relative assimilation is somewhat concentration dependent as experiments showed that as exposure concentration increased, a greater percentage of methylmercury was found in the cytoplasm of phytoplankton cells, resulting in a higher concentration in the copepods feeding on these cells. Additionally, food quality influenced assimilation by invertebrates. During decay of a T. weissflogii culture, which served as food for the invertebrates, copepods were increasingly less able to assimilate the methylmercury from the food, while even at advanced stages of decay, amphipods were able to assimilate mercury from their food to a high degree. Finally, fish feeding on copepods assimilated methylmercury more efficiently than inorganic mercury owing to the larger fraction of methylmercury found in the soft tissues of the copepods.     

Methylmercury distribution in the pregnant rat and embryo during early midbrain organogenesis

BACKGROUND: The period of neurogenesis represents a window of susceptibility for in utero methylmercury (MeHg) exposure. This study examined the toxicokinetics of potentially neurotoxic doses of MeHg during neurogenesis in the developing rat to provide additional information in the areas of mercury speciation and inter-study variability. METHODS: Pregnant Sprague-Dawley rats were dosed s.c. with 5-22 mg/kg MeHg on Day 11 of gestation to target rapidly dividing cells of the developing midbrain. Maternal liver, kidney, skin, blood, placenta, and the embryonic body and brain were evaluated for total and inorganic mercury content at 24, 48, and 72 hr after dosing. Tissue Hg partitioning ratios derived from our data were then compared to those derived from previous studies. RESULTS: Mercury was present in all tissues examined by 24 hr after dosing, and levels remained relatively stable over the subsequent 2 days in most tissues. The exceptions were the maternal blood and kidney, in which total mercury decreased significantly over the three days after dosing. Inorganic mercury concentrations were similarly stable over time. At maternal MeHg doses above 12 mg/kg, non-linearities were observed in mercury accumulation in the embryo, placenta and maternal liver. The mercury tissue partitioning coefficients ranged from 0.09 for maternal blood:embryo to 1.97 for maternal blood:kidney. CONCLUSIONS: Our observations at the 5 mg/kg dose were consistent with those of previous studies that involved evaluations at slightly later gestational times. The estimates of tissue partitioning coefficients we derived using multiple studies provide valuable insight into the effects of inter-study variability.     

Variations in larval growth and metabolism of an estuarine shrimp Palaemonetes pugio during toxicosis by an insect growth regulator

1. Exposure of the estuarine shrimp, Palaemonetes pugio, to a juvenile hormone analogue (⩾8 μg methoprene 1⁻¹) throughout larval development inhibited successful completion of metamorphosis.2. Methoprene exposure retarded growth in early larval stages and postlarvae, but enhanced growth in premetamorphic larvae.3. Respiration rates of early larvae were elevated by methoprene exposure, but not so older larvae or post larvae.4. Lower net growth efficiency (K₂ values) in methoprene-exposed early larvae suggests that increased metabolic demands reduced assimilated energy available for growth.5. Modifications in O:N ratios of premetamorphic larvae and postlarvae suggest that methoprene altered substrate utilization patterns during metamorphosis.     

Kinetics and fates of ammonia, urea, and uric acid during oocyte maturation and ontogeny of the Atlantic halibut (Hippoglossus hippoglossus L.)

Considering that amino acids constitute an important energy fuel during early life of the Atlantic halibut (Hippoglossus hippoglossus L.), it is of interest to understand how the nitrogenous end products are handled. In this study we focused on the kinetics and fates of ammonia, urea and uric acid. The results showed that ammonia (T(Amm): NH(3)+NH(4)(+)), and urea-N contents increased during final oocyte maturation. Urea-N excretion dominated the total nitrogenous end product formation in early embryos. Later, yolk T(Amm) levels increased in embryos and ammonia excretion was low. In the last part of the embryonic stage T(Amm) accumulation dominated, and was apparently due to yolk storage. Around hatching, the larval body tissues (larva with yolk-sac removed) accounted for 68% of whole animal urea-N accumulation, while T(Amm) levels increased predominately by yolk accumulation. Afterwards, ammonia excretion dominated and uric acid accumulation accounted for less than 1%. Urea, synthesised either through the ornithine-urea cycle, argininolysis or uricolysis, accounted for approximately 8% of total nitrogenous end product formation in yolk-sac larvae. The results suggested that a sequence occurred regarding which nitrogenous end products dominated and how they were handled. Urea excretion dominated in early embryos (<7 dPF), followed by yolk ammonia accumulation (7-12 dPF), and finally, ammonia excretion dominated in later embryonic and yolk-sac larval stages (>12 dPF).     

The effects of different cold‐temperature regimes on development,growth, and susceptibility to an abiotic and biotic stressor

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Effect of ultraviolet radiation on growth and percent settlement of larval Lytechinus variegatus (Echinodermata: Echinoidea)

Lytechinus variegatus larvae were used to examine the effects of ecologically relevant short-term exposures of ultraviolet radiation (UVR) on larval morphology and settlement. A laboratory experiment tested the blastula, gastrula, and early pluteus stages of larval development for susceptibility to damage from exposure to UVR produced by an artificial light source. Larval post-oral arm length and percent settlement were measured to assess UVR effects. Larvae exposed at the blastula and gastrula stages had a reduction in larval post-oral arm length compared with non-exposure controls, while larvae exposed at the early pluteus stage were similar to controls. Larvae exposed in the gastrula stage had a significant reduction in percent settlement compared with controls. Negative consequences from ecologically relevant levels of UVR were differentially dependent on the larval stage at time of exposure suggesting time point in larval development at exposure will be important in interpreting effects on higher levels of biological organization.     

Will climate change reduce the effects of a pesticide on amphibians?: partitioning effects on exposure and susceptibility to contaminants

Several studies suggest that global climate change could increase the toxicity of contaminants, but none of these studies explicitly integrate the effects of climate change on both susceptibility and duration of exposure to pollution. For many amphibian and aquatic insect species, exposure to contaminants is probably greatest during their fully aquatic embryonic and larval stages because these stages cannot readily escape water bodies where many contaminants accumulate and concentrate. Hence, by accelerating embryonic and larval development, global warming might reduce the duration of contaminant exposure for these taxa. To test this hypothesis, we isolated the effects of a temperature gradient (13–25 °C) on susceptibility (toxicity at a controlled exposure duration) and exposure of the streamside salamander, Ambystoma barbouri, to the herbicide atrazine (0, 4, 40, and 400 μg L^?1) by quantifying growth, survival, hatching, and metamorphosis under an atrazine exposure duration that was either constant or that depended on time to metamorphosis (and thus temperature). Increasing atrazine concentrations reduced growth, delayed hatching and metamorphosis, and decreased embryonic and larval survival. Increasing temperatures enhanced growth, accelerated development, and reduced survival for embryos but not larvae. With the exception of growth, increasing temperatures generally did not enhance the toxicity of atrazine, but they did generally ameliorate the adverse effects of atrazine by accelerating development and reducing the duration of atrazine exposure. The actual effects of climate change on contaminants remains difficult to predict because temperature changes can affect chemical use, uptake, excretion, biotransformation, fate, transport, and bioavailability. However, this work highlights the importance of explicitly considering how climate change will affect both exposure and toxicity to contaminants to accurately assess risk.     

Tyndallblau-Struktur von Federn im Elektronenmikroskop

Summary The normal development and cytology of the pineal organ in the newt, Taricha torosa has been described in detail. Particular emphasis has been placed on the origin of the initial pineal bud in the embryonic diencephalic roof, and the manner in which new pineal cells are proliferated in a zone surrounding the orifice of the developing pineal vesicle. These new cells apparently migrate into the walls of the enlarging vesicle and a certain number undergo progressive differentiation to become photoreceptor-like pineal sensory cells; the highest degree of this differentiation being obtained by cells whose processes protrude into the anterior, posterior, and lateral margins of the vesicle lumen.The well-formed, wide-lumened vesicle typical of early larval stages has thusfar not demonstrated any detectable cytological alterations under the influence of light, dark, pressure, or chemical stimulating agents we have employed. Within a few weeks, this young larval vesicle becomes flattened to assume the appearance of a more glial vascularized organ. In adult pineal organs it has been possible to observe aldehyde fuchsin-positive accumulations in the processes of supportive cells terminating near capillary walls. Other aspects of adult pineal cytology and innervation have also been considered in this report.A series of implants of embryonic pineal primordia into older larval host eye chambers and tailfins has given information on the development of vesicles in these sites under the influence of varying amounts of diencephalic roof tissue included with the grafts. A tentative hypothesis has been formulated to account for the tendency of a single primordium to differentiate into a larger than normal pineal mass when implanted into the tail mesenchyme with a moderate amount of diencephalic roof tissue. This hypothesis brings into focus the normal growth characteristics of the young organ developing from a broad initial pineal field and their possible modification under the influence of surrounding tissues during normal ontogeny.Incidental to the main purposes of the study, observations have been made on the pigment behavior of larvae carrying supernumerary pineal implants. These observations are discussed in the light of recent proposals by other authors.With technical assistance of Mr. Charles Cintron, Mr. Gary Clark, Miss Jean Ewalt, and Mr. Paul Johnson. The author has also been fortunate to have the interest and suggestions of Dr. Stuart Smith. Since a portion of this study was accomplished at the Zoological Laboratory, Utrecht, Holland, special thanks are due the members of that organization for their hospitality and technical advice.Portions of this research were supported by a post-doctoral fellowship (BF7283-C) from the United States Public Health Service, a research grant (G-14423) from the National Science Foundation, and grants from the University of Colorado Council on Research and Creative Work.     

Compensating for delayed hatching across consecutive life‐history stages in an amphibian

Environmental conditions experienced early in the ontogeny can have a strong impact on individual fitness and performance later in life. Organisms may counteract the negative effects of poor developmental conditions by developing compensatory responses in growth and development. However, previous studies on compensatory responses have largely ignored the effects that poor embryonic conditions could have during the later life stages. In this study, we examined the effects of artificially delayed development in early life over two later life history transitions by investigating the compensatory growth of larval moor frogs Rana arvalis in response to temperature variation during embryonic development, and the associated costs during the larval ′and postmetamorphic stages. Low temperature during embryonic stage lead to delayed hatching at smaller size. The groups with delayed embryonic development showed strong compensatory growth during the larval stage, and reached similar metamorphic size than the controls in a shorter time. However, the most strongly delayed group was not able to fully catch up the total development time. These compensatory responses were found in the absence of photoperiod cues indicating that the delay in embryonic development was sufficient to initiate the compensatory response in larval growth and development. No apparent costs of compensatory growth were detected in terms of morphology or locomotor performance at the juvenile stage. We found that compensatory responses can be activated as early as at the embryonic stage and extend over several consecutive life history transitions, mitigating the effects of poor conditions experienced early in development. Potential short‐term costs in natural environments and the occurrence of long‐term costs, which prevent the generalisation of a faster larval life style, are discussed.     

Accumulation of methylmercury and inorganic mercury in the brain

Differences in metabolism between different mercury species are well recognized. Conclusions that only a minor demethylation of methylmercury takes place in the brain are based primarily on results from short term studies. Results from a number of studies on humans exposed for many years to methylmercury have shown high concentrations of inorganic mercury in the brain in relation to total mercury. Similar evidence is available from studies on monkeys exposed for several years to methylmercury. The results indicate that a significant accumulation of inorganic mercury takes place with time despite the fact that the demethylation rate is slow. Differences in biological halftimes between different mercury species will explain the results. Some data do still need confirmation using different analytical methods. There is reason to believe that the one-compartment model for methyl mercury cannot be used without reservations. Inorganic mercury has a complicated metabolism. After exposure to metallic mercury vapor, inorganic mercury, probably bound to selenium, accumulates in the brain. A fraction of the mercury is excreted, with a long biological halftime. Studies on rats and monkeys indicate that inorganic mercury penetrates the blood-brain barrier only to a very limited-extent.     

Cross habituation to feeding deterrents and acceptance of a marginal host plant byPieris rapae larvae

Sensitivity of the cabbage butterfly,Pieris rapae L. to feeding deterrents was compared for larvae reared on different food sources under laboratory conditions. Since cabbage-reared larvae normally reject nasturtium,Tropaeolum majus L., the effects of previous exposure to allelochemicals on larval acceptance or rejection of this plant were also examined. When compared with cabbage-reared larvae, nasturtium-reared larvae were less sensitive to feeding deterrents including cymarin, erysimoside and 2-O-β-d-glucosyl cucurbitacin E. Nasturtium-reared larvae were insensitive to chlorogenic acid, which was deterrent to cabbage-reared larvae. Feeding by larvae reared on a wheat germ diet was not deterred by these compounds. The results indicate that dietary experience can extensively affect larval sensitivity to feeding deterrents and that cross habituation of larvae to deterrents occurs in response to certain chemical constituents of nasturtium and wheat germ diet. Digitoxin, however, proved to be an exception. Larvae reared on either nasturtium or wheat germ diet were as sensitive to digitoxin as those reared on cabbage. Previous results have shown that rejectionof nasturtium by cabbage-reared larvae is due to the presence of strong feeding deterrents in this plant. However, more than 50% of 2nd instar larvae reared from neonate on cabbage leaves treated with strophanthidin, cymarin, erysimoside, digitoxigenin and digitoxin accepted nasturtium as a food source. 2-O-β-d-glucosyl cucurbitacin E, 2-O-β-d-glucosyl cucurbitacin I and rutin were also active in causing larvae to feed on nasturtium. Thus dietary exposure to unrelated plant chemicals can profoundly affect insect acceptance of a plant that contains feeding deterrents.     

Carryover effects of predation risk on postembryonic life-history stages in a freshwater shrimp

For organisms with complex life histories it is well known that risk experienced early in life, as embryos or larvae, may have effects throughout the life cycle. Although carryover effects have been well documented in invertebrates with different levels of parental care, there are few examples of predator-induced responses in externally brooded embryos. Here, we studied the effects of nonlethal predation risk throughout the embryonic development of newly spawned eggs carried by female shrimp on the timing of egg hatching, hatchling morphology, larval development and juvenile morphology. We also determined maternal body mass at the end of the embryonic period. Exposure to predation risk cues during embryonic development led to larger larvae which also had longer rostra but reached the juvenile stage sooner, at a smaller size and with shorter rostra. There was no difference in hatching timing, but changes in larval morphology and developmental timing showed that the embryos had perceived waterborne substances indicative of predation risk. In addition to carryover effects on larval and juvenile stages, predation threat provoked a decrease of body mass in mothers exposed to predator cues while brooding. Our results suggest that risk-exposed embryos were able to recognize the same infochemicals as their mothers, manifesting a response in the free-living larval stage. Thus, future studies assessing anti-predator phenotypes should include embryonic development, which seems to determine the morphology and developmental time of subsequent life-history stages according to perceived environmental conditions.     

Developmental potencies of nuclei from cleavage,preblastoderm, and syncytial blastoderm transplanted into unfertilized eggs ofDrosophila melanogaster

Summary Wild-type nuclei from eggs ofDrosophila melanogaster at various developmental stages and from different regions of the egg—cleavage nuclei, pole nuclei from preblastoderm, and lateral nuclei from syncytial blastoderm—were singly implanted into unfertilizedy w sn ³ lz _50e eggs to determine their developmental potencies.All three types of transplanted nuclei were almost equally effective in initiating development of unfertilized eggs. Development was arrested in one of five critieal embryonic stages or in one of the three larval instars. The frequency of individuals reaching a distinct stage was approximately the same for all three types of donor nuclei. The stage-specific pattern of defects was independent of the type of nucleus transplanted.The deviations from normal development were broadly similar to those seen in controls developing from fertilized eggs which had only been punctured or into which cytoplasm had been injected. Many defective embryos also occurred in these control experiments. These and other observations indicate that a large proportion of irregularly developed individuals found after nuclear transfer can be ascribed to loss of egg material, disturbances in the internal organization of the egg during nuclear implantation, and the difficulty the implanted nucleus has in adjusting to the autonomous processes within the egg, such as the formation and migration of cytoplasmic islands.Some of the defective embryos and larvae originating from nuclear transfer were implanted into adult hosts. After culture for 14 days the early embryonic stages had formed several larval structures, and the late embryonic and larval stages had developed all larval organs. The proliferated imaginal primordia of thesein vivo cultured embryos and larvae, as well as the imaginal disks of the third instar larva, were then implanted into larval hosts with which they passed through metamorphosis and differentiated into imaginal structures. All three types of donor nuclei were capable of producing all adult structures derivedin situ from imaginal disks. The phenotype of these structures waswild-type, thus demonstrating their origin from the transplanted nuclei.The problem as to why not all transplanted nuclei initiated development, and why development after nuclear transplantation was arrested at the third larval instar, at the latest, is discussed.This article is dedicated to Professor Friedrich Seidel on the occasion of his 75th birthday.