Larval Life Span Research Articles

Evolutionary ecology of learning: insights from fruit flies

AbstractEcologically and evolutionarily oriented research on learning has traditionally been carried out on vertebrates and bees. While less sophisticated than those animals, fruit flies (Drosophila) are capable of several forms of learning, and have the advantage of a short generation time, which makes them an ideal system for experimental evolution studies. This review summarizes the insights into evolutionary questions about learning gained in the last decade from evolutionary experiments on Drosophila. These experiments demonstrate that Drosophila has the genetic potential to evolve a substantially improved learning performance in ecologically relevant learning tasks. In at least one set of selected populations, the improved learning generalized to a task other than that used to impose selection, involving a different behavior, different stimuli, and a different sensory channel for the aversive reinforcement. This improvement in learning ability was associated with reductions in other fitness‐related traits, such as larval competitive ability and lifespan, pointing to evolutionary trade‐offs for improved learning. These trade‐offs were confirmed by other evolutionary experiments where a reduction in learning performance was observed as a correlated response to selection for tolerance to larval nutritional stress or for delayed aging. Such trade‐offs could be one reason why fruit flies have not fully used up their evolutionary potential for learning. Finally, another evolutionary experiment with Drosophila provided the first direct evidence for the long‐standing idea that learning can under some circumstances accelerate and in others slow down genetically based evolutionary change. These results demonstrate the usefulness of fruit flies as a model system to address evolutionary questions about learning.

Spawning and development in Osedax boneworms (Siboglinidae, Annelida)

We report observations on spawning and early development in bone-eating worms of the genus Osedax. Individual females of Osedax rubiplumus were observed at 1820 m depth freely spawning hundreds of oocytes, and females of an undescribed species, Osedax “orange collar”, were observed spawning in laboratory aquaria. Cytological and molecular analysis of the spawned oocytes of two Osedax species revealed no evidence for the bacterial endosymbionts that the female worms require for their nutrition, suggesting that the bacteria must be acquired later from the environment, as they are in other siboglinids. Individual O. “orange collar” females released an average of 335 (±130) eggs per day, but the number of oocytes spawned per day varied greatly, suggesting that not all the females spawned daily. Fertilization rates of the spawned oocytes varied from 0 to 100%, though most females showed nearly 100% fertilization rates. Oocytes spawned in the laboratory at 4–6°C were negatively buoyant. If fertilized, these oocytes extruded polar bodies and then after at least four hours cleaved unequally. Subsequent cleavages occurred in a spiral pattern at roughly 2-h intervals, resulting in free-swimming trochophore larvae after 24 h. These lecithotrophic trochophores swam for 9–16 days before settling with several hooked chaetae, similar to those of dwarf Osedax males. The larval life span of the Osedax species studied in the laboratory appears to be shorter than in closely related Vestimentifera. Osedax rubiplumus, on the other hand, has much larger oocytes and so may have greater dispersal potential than these other Osedax species. The high fecundity and apparently continuous reproduction of Osedax boneworms permits the opportunistic exploitation of sunken vertebrate bones.

Ultrastructure and dispersal potential of sponge larvae: tufted versus evenly ciliated parenchymellae

AbstractIn this work we analyse the ultrastructure and behaviour of two representative types of parenchymella sponge larvae: the evenly ciliated larva of Scopalina lophyropoda, and the tufted larva of Cacospongia mollior. We sought to find correlates of the dispersal abilities and distribution patterns of these species. Laboratory experiments were performed under two different conditions of water movement (still water and a slight oscillatory movement), and at different times of the larval life‐span. Larvae of S. lophyropoda were motionless most of the time, maintaining a vertical posture and rotating on their main axis, and they did not respond to directional light. Larvae of C. mollior were active swimmers that responded negatively to light stimuli. In both cases, movement decreased as the larval age increased. Ultrastructurally, C. mollior larvae were more compact, with more reserves and abundant collagen bundles. Desmosome‐like structures were seen connecting the apical parts of the ciliated surface in both species. Two different types of putative light‐sensitive structures were found. Both structural and behavioural characteristics favour a greater dispersal capability for C. mollior and a philopatric dispersal mode for S. lophyropoda. These predictions are in agreement with the observed ecological distribution of the species.

Distribution and retention of Sabellaria alveolata larvae (Polychaeta: Sabellariidae) in the Bay of Mont-Saint-Michel, France

The gregarious polychaete Sabellaria alveolata is an important foundation species whose reef structures add topographic complexity and high levels of biodiversity in sandflats. In the Bay of Mont-Saint-Michel, France, S. alveolata reefs are considered the largest reef formations in Europe and are increasingly endangered by anthropogenic pressure. In order to understand the role of larval transport on the resilience capacity of these biogenic reefs, multiple complementary approaches were carried out within the bay in 2002 to study horizontal and vertical distribution of S. alveolata larvae and assess larval dispersal processes. Plankton samples collected twice a month from March to October showed an extended period of larval occurrence, from the end of April to October, with 2 peaks of high abundance. The main spawning period occurred early in May, and a smaller peak occurred in September. Mean planktonic lifetime has been calculated to be between 4 and 10 wk. At large scale, larval distribution was patchy and the maximal abundance could reach about 28 000 larvae m -2 . Larval densities were strongly correlated with physico-chemical parameters so that larvae were more abundant in a warmer and less saline coastal water mass characterised by a higher concentration in chlorophyll a. The presence of a large anticyclonic gyre in the bay seemed to play a significant role in controlling larval dispersal by concentrating larvae within the bay. At 1 station in the bay, short-term variations of larval abundances in the water column appeared to be regulated by the tidal cycle, as larvae were more abundant at the end of ebb tide, confirming the very coastal distribution of larvae. Furthermore, S. alveolata larvae tended to migrate closer to the surface during flood and near the bottom during ebb, promoting a net landward transport of larvae. Despite a long larval lifespan, our results indicate that tidal residual currents, especially a coastal gyre, and tidal vertical migration may favour larval retention within the bay.

Long‐term impacts of elevated carbon dioxide and transgenic Bt cotton on performance and feeding of three generations of cotton bollworm

AbstractThe effects of elevated carbon dioxide (CO2) on growth, metabolism, and performance of three generations of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), were studied. The insects were continuously fed transgenic Bacillus thuringiensis (Berliner) (Bt) cotton [Cry1A(c)] grown in open‐top chambers. Two levels of CO2 (ambient and 2× ambient) and two cotton cultivars (non‐transgenic Simian‐3 and transgenic Bt GK‐12) were used and bollworm larvae were reared on all four treatment combinations for three generations. CO2 level and cotton variety significantly affected the growth and food digestibility parameters of H. armigera, with the exception of larval consumption rate for cotton variety. Overall, elevated CO2 and transgenic Bt cotton both increased larval lifespan, food consumption rate, relative consumption rate, and approximate digestibility, while decreasing pupal weight, survival rate, fecundity, frass output, relative and mean relative growth rates (RGR/MRGR), and the efficiency of conversion of ingested and digested food (ECI/ECD). Moreover, there were significant CO2*variety interactions on pupal weight and ECD, and CO2*generation interactions on pupal weight, frass output, and MRGR. Furthermore, transgenic Bt cotton significantly decreased the population‐trend index compared to non‐transgenic cotton for the three successive bollworm generations, especially at elevated CO2. Damage inflicted by the cotton bollworm on cotton, irrespective of the presence of insecticidal genes, is predicted to be higher under elevated CO2 conditions because of individual compensatory feeding on host plants. Conversely, population abundance is presumed to be lower under elevated CO2 compared to that under ambient CO2, particularly in combination with transgenic technologies.

The management of metabolic energy storage during the life cycle of mayflies: a comparative field investigation of the collector-gatherer Ephemera danica and the scraper Rhithrogena semicolorata

The concentration and seasonal dynamics of the major energy storage components, triglycerides and glycogen, were measured in two species of mayfly (Rhithrogena semicolorata and Ephemera danica) with contrasting life cycle strategies living in a small mountain stream. E. danica is a burrowing, semivoltine collector-gatherer; R. semicolorata is univoltine and scrapes periphyton from stones. This is the first publication which focuses on the role of metabolic energy sources during the larval life span of two mayfly species until the larvae emerge. Although triglycerides are the major energy reserve in both species (>84% of total energy storage) throughout the whole larval development their seasonal dynamic differed considerably. In R. semicolorata the triglyceride concentration declined during the last weeks prior to emergence in both sexes. The same pattern was found in female larvae of E. danica, but not in male E. danica. It is suggested that females use triglycerides in the last larval stages for egg maturation, which is completed in the last larval instar. In male E. danica the triglyceride concentrations remained high until emergence, presumably due to their high energy demands as adults for their swarming flights. Glycogen concentrations did not show such a difference between species and sexes. Its significance as a storage substrate for energy is rather low; however, concentrations decreased in both species and sexes prior to emergence.

Response of multiple generations of cotton bollworm Helicoverpa armigera Hübner, feeding on spring wheat, to elevated CO2

Abstract: The growth, development and consumption of three successive generations of cotton bollworm, Helicoverpa armigera (Hübner), reared on milky grains of spring wheat grown under elevated CO2 (double‐ambient vs. ambient) in open‐top chambers (OTCs) were examined. Decreases in protein, total amino acid, water and nitrogen content, and increases in total non‐structure carbohydrates (TNCs) and ratio of TNC : nitrogen were found in wheat milky grains grown under elevated CO2 conditions. Changes in quality of wheat grains affected the growth, development and food utilization of H. armigera. Significantly longer larval lifespan for the third generation and lower pupal weight for all generations were observed in cotton bollworm fed on milky grains of spring wheat grown under elevated CO2 conditions. Bollworm fecundity was significantly decreased for the second and third generations under elevated CO2 levels. The consumption, frass per larva and relative consumption rate significantly increased in elevated CO2 compared with ambient CO2 conditions. However, the potential population consumption was significant reduced by elevated CO2 in the second and third generations. The results of this study indicate that elevated CO2 levels adversely affect grain quality, resulting in consistently increased consumption per larva for a longer period to produce less fecund bollworm through generations, suggesting that net damage of cotton bollworm on wheat will be less under elevated atmospheric CO2 levels because increased consumption is offset by slower development and reduced fecundity.

A new isolate of Melolontha melolontha entomopoxvirus in Turkey: Morphology, infectivity and prevalence in the field

A virus infection caused by Melolontha melolontha L. (Coleoptera: Scarabaeidae) entomopoxvirus (MmEPV) was recorded in 0.87% of 1,260 larvae collected in 2001-2002 in Trabzon, Turkey. The diseased larvae had dark brown or black and white spots, compared to the normal white-cream colour of healthy larvae. MmEPV infections reduced the larval life span from 6 mo to 15±5 d (Mean±S.D.). Based on light and electron microscopic observations, the average length of the spheroids was 5.45±2.34 μm (Mean±S.D.) and the average width was 2.89±1.13 μm (Mean±S.D.) (n=50). The presence of a virus was also demonstrated in a DNA-DNA hybridization assay. The bioassays carried out to determine the infectivity of MmEPV proved its effectiveness against the third-instar larvae of the M. melolontha. The highest insecticidal activity determined in the M. melolontha larvae was 93.3% at the concentration of 7.5×10 6 spheroids/ml. Our results suggest that a Turkish isolate of MmEPV is promising for biological control of the M. melolontha larvae.

Embryonic and larval development of a cold adapted Antarctic ascidian

Ova of the Antarctic ascidian Cnemidocarpa verrucosa were mature at 240–245 μm. At 0 to −1.5°C, embryos hatched as swimming tadpoles at 8 days from fertilization, which is close to the ages at which some Antarctic echinoderm and nemertean embryos hatch as blastulae. Comparisons of Antarctic and temperate ascidian larvae suggest that the ascidian’s development rate is affected by low environmental temperatures to about the same extent as embryos and larvae of an echinoid, nemertean, and calanoid copepods. The ascidian’s tadpoles were bright orange and large, >2 mm in length including tunic and >1.5 mm in length without tunic. The large and brightly colored tadpoles were conspicuous when swimming, which supports the hypothesis that larvae of C. verrucosa are chemically defended against predators. Metamorphosed juveniles were found in cultures within 16 days from fertilization, when some unsettled tadpoles still moved but were less active. The potential pelagic period may therefore be 16 or more days with 8 days as an unhatched embryo and up to 8 or more days as a tadpole. The resting metabolic rate of tadpole larvae was 15 pmol O2 h−1 individual−1 which is equivalent to larval respiration rates in Antarctic echinoderms. A low resting metabolic rate suggests a potential mechanism for the extended larval lifespan in C. verrucosa.

The regenerative cells during the metamorphosis in the midgut of bees

The midgut epithelium of bees is formed by the digestive cells, responsible for enzyme secretion and nutrient absorption and for small regenerative cells that are placed in nests scattered among the digestive cells. During metamorphosis, the larval midgut epithelium degenerates and a new adult midgut epithelium is built during larval differentiation of regenerative cells. The present work focuses on the midgut epithelial modifications during the post-embryonic development of the stingless bee Melipona quadrifasciata anthidioides worker and the occurrence of regenerative cell proliferation during midgut metamorphosis in order to test the hypothesis that adult midgut epithelium of worker bees results from regenerative cell proliferation during the pupal stage. Regenerative cell proliferation was detected during larval lifespan. Larval aging is followed by an increase in the number and the size of the nests of regenerative cells. Larval epithelium degeneration begins 2 days after the start of defecation process and in this period the nests of regenerative cells are in contact by means of cytoplasmic extension which have many septate desmosomes and gap junctions. The BrdU immunoreactive regenerative cells were found in the prepupae 12 h after BrdU injection, suggesting that regenerative cell population increase during this larval period. Regenerative cell proliferation results in the increase of the regenerative cell population and not in the formation of new digestive cells because the proliferation of regenerative cells would not be enough to reestablish the nests of regenerative cells and at the same time form new adult digestive cells. In this sense the hypothesis that digestive adult cells originate from regenerative cell proliferation during midgut metamorphosis in M. quadrifasciata anthidioides was rejected.

The TOR pathway interacts with the insulin signaling pathway to regulate C. elegans larval development, metabolism and life span.

The highly conserved target-of-rapamycin (TOR) protein kinases control cell growth in response to nutrients and growth factors. In mammals, TOR has been shown to interact with raptor to relay nutrient signals to downstream translation machinery. We report that in C. elegans, mutations in the genes encoding CeTOR and raptor result in dauer-like larval arrest, implying that CeTOR regulates dauer diapause. The daf-15 (raptor) and let-363 (CeTOR) mutants shift metabolism to accumulate fat, and raptor mutations extend adult life span. daf-15 transcription is regulated by DAF-16, a FOXO transcription factor that is in turn regulated by daf-2 insulin/IGF signaling. This is a new mechanism that regulates the TOR pathway. Thus, DAF-2 insulin/IGF signaling and nutrient signaling converge on DAF-15 (raptor) to regulate C. elegans larval development, metabolism and life span.

Apical sensory neurones mediate developmental retardation induced by conspecific environmental stimuli in freshwater pulmonate snails.

Freshwater pond snails Helisoma trivolvis and Lymnaea stagnalis undergo larval development and metamorphosis inside egg capsules. We report that their development is permanently under slight tonic inhibitory influence of the anterior sensory monoaminergic neurones, which are the remnants of the apical sensory organ. Conspecific juvenile snails, when reared under conditions of starvation and crowding, release chemical signals that are detected by these neurones in encapsulated larvae and reversibly suppress larval development, thus providing a link between environmental signals and developmental regulation. Induced retardation starts from the trochophore stage and results in up to twofold prolongation of the larval lifespan. Upon stimulation with the signal, the neurones increase synthesis and release of monoamines [serotonin (5-HT) in Helisoma and dopamine in Lymnaea] that inhibit larval development acting via ergometrine-sensitive internal receptors. Thus, the novel regulatory mechanism in larval development of molluscs is suggested and compared with the phenomenon of dauer larvae formation in the nematode Caenorhabditis elegans.

Influence of short-term variations in food on survival of <I>Crassostrea gigas</I> larvae: A modeling study

A biochemically-based model was developed to simulate the growth, development, and metamorphosis of larvae of the Pacie c oyster, Crassostrea gigas. The model dee nes larvae in terms of their protein, lipid, carbohydrate, and ash content and includes variation in growth efe ciency and egg quality to better simulate cohort population dynamics. Changes in tissue composition occur as the larva grows and in response to the biochemical composition of the food. The premise behind this modeling study was that certain periods of larval life are more critical than others with respect to the availability of food and that food quality is as important as food quantity. The results of the simulations indicate that critical periods do exist, but that the period of larval life which is critical depends upon the composition of the available food supply and how it varies over time. Overall, the most critical time is late in larval life, near the time of metamorphosis. At this point, some variations in food quality are particularly efe cacious, others particularly disastrous. But, under certain circumstances, events early or midway in larval life also dramatically change cohort survival. Simulations show that cohort survival varies in a relatively predictable way when salinity or food quantity vary. Both control time-integrated food supply to the larva by varying the amount of food ingested. Reduction of time-integrated ingestion reduces survival. Larvae with high growth efe ciency are more successful, as are larvae coming from large eggs. The simple effect of timeintegrated food presents a stark contrast to the complexity introduced by varying food quality. Simulations indicate that it is late in larval life when larvae are most sensitive to changes in food quality. Increased protein at this time always improves survival. Increased lipid is most efe cacious midway in larval life, but also exerts a positive impact late in larval life. Variations in carbohydrate are relatively inconsequential in affecting larval survival. Simulations in which food quantity and food quality vary independently show that cohort survival is sensitive to the exact timing and type of environmental change. Transient changes in food quantity ine uence survival primarily by varying the length of larval life. Transient changes in food quality, on the other hand, can produce large changes in survivorship by restricting the range of genotypes in the cohort that can survive, as well as by varying larval life span. The simulations support the adaptive advantage of larval cohorts with a relatively wide range of genotypes and suggest the important ine uence of variations in food quality in maintaining genetic variability.

A modelling study of the influence of environment and food supply on survival of Crassostrea gigas larvae

AbstractA biochemically based model was developed to simulate the growth, development, and metamorphosis of larvae of the Pacific oyster (Crassostrea gigas). The unique characteristics of the model are that it: (1) defines larvae in terms of their protein, neutral lipid, polar lipid, carbohydrate, and ash content; (2) tracks weight separately from length to follow larval condition; and (3) includes genetic variation in growth efficiency and egg quality to better simulate cohort population dynamics. The model includes parameterizations for filtration, ingestion, and respiration, which determine larval growth rate, and processes controlling larval mortality and metamorphosis. Changes in larval tissue composition occur as the larva grows and in response to the biochemical composition of the food.Simulations of larval growth indicate that departures of temperature, salinity, or food content from optimum levels reduce larval cohort survival, either because of metabolic constraints that result in death, unsuccessful metamorphosis, or increased predation resulting from increased larval lifespan. Temperatures and salinities near optimal values improve larval survival at low food concentration by increasing ingestion rate or growth efficiency. Also, survival at a given food concentration can vary widely depending on food composition, which determines food quality. The simulations suggest that the ratio of carbohydrate + lipid-to-protein may best describe the overall food quality, with optimal food compositions being characterized by ratios near 1.2 to 1.4 over a range of food concentrations. In contrast, food compositions containing too much or too little protein reduce larval survival, even at saturating food concentrations.In simulations emphasizing genetic variability within the cohort, larvae with high growth efficiency originating from large eggs out-perform other egg quality–growth efficiency combinations over a wide range of temperature, salinity, and food contents. As a consequence, suboptimal temperature, salinity, or food content compresses genetic variation by uniformly favouring larvae from large eggs with a high growth efficiency. However, the larval survival obtained from simulations that use a range of food qualities is representative of a much broader range of genetic types. Thus, the simulations support the supposition that food quality is an important variable controlling the survival and genetic variability of C. gigas larval cohorts.

MASSIVE PREY RECRUITMENT AND THE CONTROL OF ROCKY SUBTIDAL COMMUNITIES ON LARGE SPATIAL SCALES

What drives community change on large spatial scales? An opportunity to address this fundamental question was provided by a massive subtidal recruitment of the mussel, Mytilus edulis, across the southwest Gulf of Maine (GOM), USA, in 1995. Since M. edulis is consumed by many predator species, we hypothesized that the episodic increase in food resources had a bottom-up effect on populations of mussel consumers. The mussel recruitment event was unprecedented in its large spatial extent, high coverage of the sea floor, and depth of penetration into the rocky subtidal zone. During 1995-1997 we tracked mussels and their consumer populations in the area to document what happened. Surveys across a 120-km marine landscape revealed that juvenile mussels covered 33-91% of the bottom (8-12 m depth) at 13 of 17 sites between October 1995 and June 1996. The cover of mussel prey in June 1996 explained significant variation in the density and biomass of mussel predators, the sea stars Asterias spp. and rock crabs Cancer spp., at 16-17 sites 10, 13, and 23 months after mussel recruitment. These results are consistent with the hypothesis that the extensive mussel recruitment had a bottom-up effect on the subtidal food web. Levels of Asterias spp. recruitment, biomass, and density following mussel recruitment were the highest recorded at two monitored sites in 16-18 years. One year after the large pulse of mussel food resources, Asterias spp. recruitment was positively related to the percent cover of mussels, suggesting a feedback between food supply and consumer re- cruitment on a large spatial scale. Crab size-structure data supported the interpretation that recruitment contributed to the high densities of rock crabs recorded in July 1997. We suggest that the bottom-up effects observed in consumer populations were produced by increased growth, elevated reproduction and recruitment, and possibly by immigration. Coupling between bottom-up and top-down control was observed after a lag of 12-14 months post-mussel recruitment when predation by sea stars, rock crabs, and sea urchins eliminated extensive beds of juvenile mussels across the study region. The elimination of Mytilus prey triggered cannibalism in the sea star Asterias vulgaris, which contributed to density-dependent population declines in sea stars between 1996 and 1997. A key as- sumption of a consumer reproduction and recruitment response—that some of the larvae produced by local adult stocks of consumers could be retained in the study region—was tested by investigating the potential larval dispersal of sea stars and crabs in a simulated three-dimensional flow field of the southwest GOM. The simulation supported the as- sumption as 15-75% of particles released below 1-m depth were retained in the region over 2-5 week periods approximating the larval life-span of the consumers. Furthermore, the degree of retention increased dramatically between the surface (1 m) and 15-m depth, implying that the extent of large-scale connectivity by passive larval dispersal is highly dependent on depth. In this study, massive prey recruitment stimulated coupling between bottom-up and top-down forces, resulting in broad-scale changes in local consumer pop- ulations that persisted after the prey-recruitment signal was removed, underscoring the importance of episodic events in marine community dynamics.

Pelagic dispersal of the brittle-star Ophiothrix fragilis larvae in a megatidal area (English Channel, France) examined using an advection/diffusion model

The brittle-star Ophiothrix fragilis (Abildgaard) is widely distributed in the English Channel and particularly on pebble areas which are characterised by strong tidal currents. The main populations are located between 20 and 80 m depth. Although larval dispersal and settlement are apparently under an unfavourable high hydrodynamical constraint (a megatidal regime which generates high tidal currents, and a northeastward tidal residual current from the English Channel to the North Sea which advects larvae away from the adult populations), the density of adult populations showed little year-to-year variability. In order to determine the origin of ophioplutei larvae and recruitment patterns, larval dispersal from eight populations in the English Channel was simulated using a 2D hydrodynamical Lagrangian model integrating both the tidal residual, the wind-driven circulation and the eddy-diffusion. Simulations showed different transport patterns of the passive O. fragilis larvae under advection and eddy-diffusion control in the English Channel and highlighted a significant role of wind forcing on larval dispersal. Larval losses by mortality could exceed losses by hydrodynamic processes. For almost all populations, larval retention appeared to be sufficient to ensure local recruitment regardless of meteorological conditions or larval life span, and to explain the inter-annual stability of adult stocks. The degree of connection among populations was highly variable. While some populations were mainly self-seeding, larval supply from neighbouring populations could exceed local retention for other populations depending on wind forcing.

Expression of a unique drug-resistant Hsp90 ortholog by the nematode Caenorhabditis elegans.

In all species studied to date, the function of heat shock protein 90 (Hsp90), a ubiquitous and evolutionarily conserved molecular chaperone, is inhibited selectively by the natural product drugs geldanamycin (GA) and radicicol. Crystal structures of the N-terminal region of yeast and human Hsp90 have revealed that these compounds interact with the chaperone in a Bergerat-type adenine nucleotide-binding fold shared throughout the gyrase, Hsp90, histidine kinase mutL (GHKL) superfamily of adenosine triphosphatases. To better understand the consequences of disrupting Hsp90 function in a genetically tractable multicellular organism, we exposed the soil-dwelling nematode Caenorhabditis elegans to GA under a variety of conditions designed to optimize drug uptake. Mutations in the gene encoding C elegans Hsp90 affect larval viability, dauer development, fertility, and life span. However, exposure of worms to GA produced no discernable phenotypes, although the amino acid sequence of worm Hsp90 is 85% homologous to that of human Hsp90. Consistent with this observation, we found that solid phase-immobilized GA failed to bind worm Hsp90 from worm protein extracts or when translated in a rabbit reticulocyte lysate system. Further, affinity precipitation studies using chimeric worm-vertebrate fusion proteins or worm C-terminal truncations expressed in reticulocyte lysate revealed that the conserved nucleotide-binding fold of worm Hsp90 exhibits the novel ability to bind adenosine triphosphate but not GA. Despite its unusual GA resistance, worm Hsp90 appeared fully functional when expressed in a vertebrate background. It heterodimerized with its vertebrate counterpart and showed no evidence of compromising its essential cellular functions. Heterologous expression of worm Hsp90 in tumor cells, however, did not render them GA resistant. These findings provide new insights into the nature of unusual N-terminal nucleotide-binding fold of Hsp90 and suggest that target-related drug resistance is unlikely to emerge in patients receiving GA-like chemotherapeutic agents.

DAF-9, a cytochrome P450 regulating C. elegans larval development and adult longevity.

The daf-9 gene functions to integrate transforming growth factor-beta and insulin-like signaling pathways to regulate Caenorhabditis elegans larval development. Mutations in daf-9 result in transient dauer-like larval arrest, abnormal reproductive development, molting defects and increased adult longevity. The phenotype is sterol-dependent, and dependent on the activity of DAF-12, a nuclear hormone receptor. Genetic tests show that daf-9 is upstream of daf-12 in the genetic pathways for larval development and adult longevity. daf-9 encodes a cytochrome P450 related to those involved in biosynthesis of steroid hormones in mammals. We propose that it specifies a step in the biosynthetic pathway for a DAF-12 ligand, which might be a steroid. The surprising cellular specificity of daf-9 expression (predominantly in two sensory neurons) supports a previously unrecognized role for these cells in neuroendocrine control of larval development, reproduction and life span.

Influence of food quality and quantity on the growth and development of Crassostrea gigas larvae: a modeling approach

A biochemically based model was developed to simulate the growth, development and metamorphosis of larvae of the Pacific oyster, Crassostrea gigas. The model is unique in that it (1) defines larvae in terms of their protein, neutral lipid, polar lipid, carbohydrate and ash content; (2) tracks weight separately from length to follow larval condition index and (3) includes genetic variation in growth efficiency and egg quality to better simulate cohort population dynamics. The model includes parameterizations for larval filtration, ingestion and respiration that determine growth rate and processes controlling larval mortality and metamorphosis. Changes in tissue composition occur as the larva grows and in response to the biochemical composition of the food. The simulations show that genetically determined variations in growth efficiency produce significant changes in larval survival and success at metamorphosis. Larvae with low growth efficiency are successful under a much narrower range of culture conditions than larvae with high growth efficiency. The impact of low growth efficiency is primarily controlled by the ability of larvae to store lipid for metamorphosis. Culture conditions that provide increased dietary lipid counterweigh low growth efficiency. Changes in food quantity and quality had little effect on size at metamorphosis. On the other hand, larval life span and success rate at metamorphosis varied over a wide range depending upon the conditions of the simulation. Food quality and food availability both influence larval life span and, hence, larval survival. As ingestion rate decreases, larval life span increases and cohort survival declines. Increased lipid or decreased protein in the diet improves cohort survival. Changes in carbohydrate content are less influential. If cohort success is significantly affected by mortality during larval life rather than success at metamorphosis, the influence of food quality becomes more complex. The range of food compositions yielding high survival is restricted by a balance between improved success at metamorphosis obtained by increased lipid storage and the shortening of larval life span as a result of more rapid growth, a function of protein availability. These simulations illustrate the strength and utility of numerical models for evaluating and designing hatchery protocols for optimizing yield of C. gigas larvae.

Na+/K+-ATPase activity during early development and growth of an Antarctic sea urchin.

In Antarctic environments, the physiological bases for long larval life spans under natural conditions of limited food availability are not understood. The Na+ pump is likely to be involved with hypometabolic regulation in such cold environments. Changes in the activity and metabolic importance of Na+/K+-ATPase were measured in embryos of the Antarctic sea urchin Sterechinus neumayeri and in larvae reared under different feeding conditions. The rate of increase of total Na+/K+-ATPase activity was 3.9 times faster in fed than in unfed larvae. During development and growth, there was an increase in the percentage of total, potential Na+/K+-ATPase activity that was physiologically utilized. In early (10-day-old) gastrulae, 17 % was utilized in vivo, increasing to 77 % in six-arm pluteus (48-day-old) larvae. The metabolic importance of in vivo Na+/K+-ATPase activity also increased during development, accounting for 12 % of metabolic rate at day 10 and 84 % at day 48. When compared at the same enzyme assay temperature (15 degrees C), the protein-specific total Na+/K+-ATPase activities for late embryonic (prism) and early larval (pluteus) stages of S. neumayeri were 2.6 times lower than those for comparable developmental stages of two temperate sea urchin species (Strongylocentrotus purpuratus and Lytechinus pictus).