Starvation affects vitellogenin production but not vitellogenin mRNA levels in the lubber grasshopper, Romalea microptera

Effects of oral exposure to brake wear particulate matter on the springtail Orthonychiurus folsomi

Most of the heavy metals in urban environments derives from road traffic, particularly from tyres and brake wear (non-exhaust emission sources). These pollutants contaminate the soil, where several organisms have a primary ecosystem role (e.g., springtails, ants, earthworms). Springtails (Collembola) are soil-dwelling animals regulating soil fertility, flow of energy through above- and below-ground food webs, and they contribute to soil microbial community dispersion and biodiversity maintenance. In this study we investigated the ecotoxicological effects of oral exposure to particles emitted from brake pads and cast-iron brake discs in the euedaphic collembola species Orthonychiurus folsomi under laboratory conditions. Our results showed that chronic exposure to brake wear particles can have sub-lethal effects both at low and high concentrations and it can cause histological alterations. Here, SEM-EDX was applied to observe the particulate and we found its chemical markers in the gut and faeces of collembola, while histological analysis detected alterations of the digestive and reproductive systems and of the abdominal fat body at high concentrations.

Honeybees are buffered against undernourishment during larval stages

The negative impact of juvenile undernourishment on adult behavior has been well reported for vertebrates, but relatively little is known about invertebrates. In honeybees, nutrition has long been known to affect task performance and timing of behavioral transitions. Whether and how a dietary restriction during larval development affects the task performance of adult honeybees is largely unknown. We raised honeybees in-vitro, varying the amount of a standardized diet (150 µl, 160 µl, 180 µl in total). Emerging adults were marked and inserted into established colonies. Behavioral performance of nurse bees and foragers was investigated and physiological factors known to be involved in the regulation of social organization were quantified. Surprisingly, adult honeybees raised under different feeding regimes did not differ in any of the behaviors observed. No differences were observed in physiological parameters apart from weight. Honeybees were lighter when undernourished (150 µl), while they were heavier under the overfed treatment (180 µl) compared to the control group raised under a normal diet (160 µl). These data suggest that dietary restrictions during larval development do not affect task performance or physiology in this social insect despite producing clear effects on adult weight. We speculate that possible effects of larval undernourishment might be compensated during the early period of adult life.

Proteomic changes in various organs of Haemaphysalis longicornis under long-term starvation

Haemaphysalis longicornis (Neumann), a tick of public health and veterinary importance, spend the major part of their life cycle off-host, especially the adult host-seeking period. Thus, they have to contend with prolonged starvation. Here, we investigated the underlying molecular mechanism of tick starvation endurance in the salivary glands, midguts, ovaries, and Malpighian tubules of starved H. longicornis ticks using the data-independent acquisition quantitative proteomic approach to study the proteome changes. Essential synthases such as glutamate synthase, citrate synthase, and ATP synthase were up-regulated probably due to increased proteolysis and amino acid catabolism during starvation. The up-regulation of succinate dehydrogenase, ATP synthase, cytochrome c oxidase, and ADP/ATP translocase closely fits with an increased oxidative phosphorylation function during starvation. The differential expression of superoxide dismutase, glutathione reductase, glutathione S-transferase, thioredoxin, and peroxiredoxin indicated fasting-induced oxidative stress. The up-regulation of heat shock proteins could imply the activation of a protective mechanism that checks excessive protein breakdown during starvation stress. The results of this study could provide useful information about the vulnerabilities of ticks that could aid in tick control efforts.

Ticks are a common blood-sucking parasite, which spread many pathogens that cause serious diseases such as Lyme disease to people. Ixodid ticks can take up to three blood meals in their life. During the long process of waiting for their host in the wild, they have evolved a strong ability to tolerate hunger, which should not take more than a year. To study these tenacious molecular regulatory mechanisms, we conducted the DIA quantitative proteomics technology to perform large-scale protein quantitative research on various tissues of Haemaphysalis longicornis starved for a long time. Through the analysis of thousands of proteins produced by the performed research, the results showed that many proteins in the ticks starved for a long time had expressed quantitative changes such as the increased expression of some synthase enzymes. The large amount of data provided by this study can help to better understand the molecular mechanism of ticks’ long-term hunger tolerance. Although this study focuses on finding possible mechanisms for tick starvation resistance at the protein level, the current findings may well have a bearing on research about special activities such as ultra long-distance space travel in the dormant state of the human body in the future.

Cnaphalocrocis medinalis Moths Decide to Migrate when Suffering Nutrient Shortage on the First Day after Emergence

Migration is a costly strategy in terms of reproduction output. Competition for limited internal resources leads to physiological management of migration-reproduction trade-offs in energy allocation. Migratory insects must choose to determine to allocate energy into reproduction or migration when confronted insufficient energy supply. Although nutrient shortage is known to stimulate insect migration to escape deteriorating habitat, little is known about when and how migratory insects make decisions when confronted by a nutritional shortage. Here Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), a migratory rice pest in eastern Asia, was used to study the effects of starvation on reproductive traits, behavioral traits and energy allocation. The result showed that one or two days’ starvation before preoviposition did not significantly reduce the fertility (total egg per female laid) and flight capability (flight duration and distance) of both sexes C. medinalis. The preoviposition period was extended significantly only if moths were starved starting on the first day after emergence. Also, take-off percentage of moths starved since their first day increased significantly, and continued to increase even if supplemental nutrients were supplied as honey solution in later days. Moths starved on the first day appeared to allocate or transfer triglycerides into the thorax to maintain the migration process: the quantity of thoracic triglycerides did not differ with age, but abdominal triglycerides decreased with age if starvation continued. These results indicate that the first day post-emergence is a critical period for C. medinalis to decide to migrate or not in response to lack of food. This furthers our understanding of the population dynamics of migratory insects under natural conditions.

Dissecting the Role of Juvenile Hormone Binding Protein in Response to Hormone and Starvation in the Cotton Bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Juvenile hormone (JH) regulates many physiological processes in insect development, diapause, and reproduction. Juvenile hormone binding protein (JHBP), the carrier partner protein of JH, is essential for the balance of JH titer to regulate the metamorphosis and development of insect. In this study, two JHBP genes were identified from Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), namely HaJHBP1 and HaJHBP2. The tissue and temporal expression pattern revealed that both HaJHBP1 and HaJHBP2 were dominantly expressed in larval fat body, and their high transcription stages were detected in fourth and fifth instars. The ingestion of methoprene, a JH analogue, significantly induced the expression of HaJHBP1 and HaJHBP2. However, both HaJHBP1 and HaJHBP2 mRNA levels were significantly downregulated after treated with a JH antagonist, precocene. When subject to starvation, larvae showed a marked suppressive effect in the expression of HaJHBP1 and HaJHBP2. These results indicate that JHBP plays a part in the JH-regulated metabolism, growth, or development in reaction to different nutritional conditions.

Discovery and functional identification of fecundity-related genes in the brown planthopper by large-scale RNA interference

Recently, transcriptome and proteome data have increasingly been used to identify potential novel genes related to insect phenotypes. However, there are few studies reporting the large-scale functional identification of such genes in insects. To identify novel genes related to fecundity in the brown planthopper (BPH), Nilaparvata lugens, 115 genes were selected from the transcriptomic and proteomic data previously obtained from high- and low-fecundity populations in our laboratory. The results of RNA interference (RNAi) feeding experiments showed that 91.21% of the genes were involved in the regulation of vitellogenin (Vg) expression and may influence BPH fecundity. After RNAi injection experiments, 12 annotated genes were confirmed as fecundity-related genes and three novel genes were identified in the BPH. Finally, C-terminal binding protein (CtBP) was shown to play an important role in BPH fecundity. Knockdown of CtBP not only led to lower survival, underdeveloped ovaries and fewer eggs laid but also resulted in a reduction in Vg protein expression. The novel gene resources gained from this study will be useful for constructing a Vg regulation network and may provide potential target genes for RNAi-based pest control.

Molecular cloning and expression of the vitellogenin gene and its correlation with ovarian development in an invasive pest Octodonta nipae on two host plants

There is an ongoing relationship between host plants and herbivores. The nutrient substances and secondary compounds found in the host plant can not only impact the growth and development process of herbivores, but, more importantly, may also affect their survival and reproductive fitness. Vitellogenesis is the core process of reproductive regulation and is generally considered as a reliable indicator for evaluating the degree of ovarian development in females. Vitellogenin (Vg) plays a critical role in the synthesis and secretion of yolk protein. In this study, the full-length cDNA of the Vg gene in an alien invasive species, the nipa palm hispid beetle Octodonta nipae Maulik (Coleoptera: Chrysomelidae) (OnVg) was cloned and, the effect of host plant on the OnVg expression level and ovarian development was investigated. The results revealed that the OnVg was highly and exclusively expressed in adult females, but barely detectable in larvae, pupae and adult males. The relative expression level of OnVg and egg hatchability were much higher in females fed on Phoenix canariensis (their preferred host) than those fed on Phoenix roebelenii. A positive correlation relationship between OnVg expression and egg hatchability was also detected. Additionally, the anatomy of the female reproductive system showed that the ovaries of individuals fed on P. canariensis were considerably more developed than in females fed on P. roebelenii. The results may be applicable to many pest management situations through reproductive disturbance by alternating host plant species or varieties or by reproductive regulation through vitellogenesis mediated by specific endocrine hormones.

Vitellogenin RNAi halts ovarian growth and diverts reproductive proteins and lipids in young grasshoppers

Reduced reproduction extends lifespan of females in many animals. To test the effects of reproduction on storage of macronutrients, we block reproductive output in the lubber grasshopper by injecting RNAi against the precursor to egg-yolk protein, vitellogenin, in early adulthood. Controls were injected with either buffer or RNAi against the major storage protein in the hemolymph, hexamerin-90. Vitellogenin RNAi greatly reduced both levels of mRNA for vitellogenin and ovarian growth, in comparison to both controls. Fat body mass was increased upon vitellogenin RNAi, but concentrations of the three hexameric storage proteins from the hemolymph were not. Surprisingly, hemolymph vitellogenin levels were increased upon vitellogenin RNAi. Total reproductive protein (hemolymph vitellogenin plus ovarian vitellin) was unchanged by vitellogenin RNAi, as reproductive protein was diverted to the hemolymph. Similarly, the increased lipid storage upon vitellogenin RNAi was largely attributable to the reduction in lipid in the ovary, due to decreased ovarian growth. A BLAST search revealed that the 515 bp sequence of vitellogenin used for RNAi had three 11 bp regions identical to the vitellogenin receptor of the cockroach Leucophaea maderae. This suggests that our treatment, in addition to reducing levels of vitellogenin transcript, may have also blocked transport of vitellogenin from the hemolymph to the ovary. This would be consistent with halted ovarian growth simultaneous with high levels of vitellogenin in the hemolymph. Nonetheless, the accumulation of vitellogenin, instead of hexameric storage proteins, is inconsistent with a simple model of the trade-off between reproduction and storage. This was observed in young females; future studies will address whether investment of proteins may shift to the soma as individuals age. Overall, our results suggest that blockage of reproduction in young grasshoppers redirects lipids to storage and reproductive proteins to the hemolymph.

Eat to reproduce: a key role for the insulin signaling pathway in adult insects

Insects, like all heterotrophic organisms, acquire from their food the nutrients that are essential for anabolic processes that lead to growth (larval stages) or reproduction (adult stage). In adult females, this nutritional input is processed and results in a very specific output, i.e., the production of fully developed eggs ready for fertilization and deposition. An important role in this input-output transition is attributed to the insulin signaling pathway (ISP). The ISP is considered to act as a sensor of the organism's nutritional status and to stimulate the progression of anabolic events when the status is positive. In several insect species belonging to different orders, the ISP has been demonstrated to positively control vitellogenesis and oocyte growth. Whether or not ISP acts herein via a mediator action of lipophilic insect hormones (ecdysteroids and juvenile hormone) remains debatable and might be differently controlled in different insect orders. Most likely, insulin-related peptides, ecdysteroids and juvenile hormone are involved in a complex regulatory network, in which they mutually influence each other and in which the insect's nutritional status is a crucial determinant of the network's output. The current review will present an overview of the regulatory role of the ISP in female insect reproduction and its interaction with other pathways involving nutrients, lipophilic hormones and neuropeptides.

Life-extending ovariectomy in grasshoppers increases somatic storage, but dietary restriction with an equivalent feeding rate does not

Reduced diet or reduced reproduction each extends lifespan in many animals. It is often thought that reduced reproduction and reduced diet may act through the same mechanisms. In grasshoppers, ovariectomy extends lifespan and reduces feeding to a level similar to that used for life extension by dietary restriction, further suggesting mechanistic overlap. Here, we measure the feeding rate of ovariectomized grasshoppers and, by manipulating feeding levels, create a sham-operated & dietary restricted group with matched daily feeding. Both groups show ~25% increased survivorship near the median age of mortality for fully fed and reproductive controls. Ovariectomy results in a doubling of fat body mass and hemolymph volume in comparison to both a feeding-matched dietary restriction group and a sham-operated & fully fed control, which do not differ from each other. Total anti-oxidant activity in the hemolymph and the skeletal muscle was unchanged upon ovariectomy or dietary restriction, so it does not appear to be a major factor in lifespan extension. Next, we measured mitochondrial counts using qPCR to determine mitochondrial cytochrome-b concentrations relative to nuclear (genomic) beta-actin. Mitochondrial counts in the ovariectomized group were lower than sham-operated and fully fed controls but not than the dietary restriction group. Last, in the fat body, transcript levels of hexamerin-90 (a hemolymph storage protein) were affected by neither ovariectomy nor dietary restriction. Hence, ovariectomy resulted in large magnitude increases in organismal storage. The matched-fed dietary restricted group differed from the ovariectomized group only in organismal storage, and not in any of the cellular parameters measured here. This study suggests that longevity via ovariectomy has distinct physiological mechanisms from longevity via dietary restriction in grasshoppers that are independent of daily feeding rate, particularly for protein and fat storage.

Neuropeptidergic regulation of reproduction in insects

Successful animal reproduction depends on multiple physiological and behavioral processes that take place in a timely and orderly manner in both mating partners. It is not only necessary that all relevant processes are well coordinated, they also need to be adjusted to external factors of abiotic and biotic nature (e.g. population density, mating partner availability). Therefore, it is not surprising that several hormonal factors play a crucial role in the regulation of animal reproductive physiology. In insects (the largest class of animals on planet Earth), lipophilic hormones, such as ecdysteroids and juvenile hormones, as well as several neuropeptides take part in this complex regulation. While some peptides can affect reproduction via an indirect action (e.g. by influencing secretion of juvenile hormone), others exert their regulatory activity by directly targeting the reproductive system. In addition to insect peptides with proven activities, several others were suggested to also play a role in the regulation of reproductive physiology. Because of the long evolutionary history of many insect orders, it is not always clear to what extent functional data obtained in a given species can be extrapolated to other insect taxa. In this paper, we will review the current knowledge concerning the neuropeptidergic regulation of insect reproduction and situate it in a more general physiological context.

Effects of a methanolic extract of the plant Haplophyllum tuberculatum and of teflubenzuron on female reproduction in the migratory locust, Locusta migratoria (Orthoptera: Oedipodinae)

The effects of a methanolic extract of the plant Haplophyllum tuberculatum (ME-Ht) and of teflubenzuron (TFB) were compared on several reproductive variables and ecdysteroid titers in the females of Locusta migratoria. The test products were administered orally to newly emerged females at doses of 1500 (ME-Ht) and 10μg/female (TFB). The methanolic extract and TFB had comparable effects on several of the variables examined. Both significantly delayed the first oviposition and reduced fecundity and fertility. ME-Ht and TFB also displayed similar effects on ovarian growth, vitellogenesis and ecdysteroid titers. Both treatments induced a drop in hemolymph protein levels as well as a reduction in vitellogenin uptake by oocytes. This delay in oogenesis was accompanied by a resorption of terminal oocytes. However, whereas TFB completely blocked egg hatch, ME-Ht only had a modest inhibitory effect on this variable. Hemolymph and ovarian ecdysteroid titers, as measured by radioimmunoassay, were similar and low in both control and treated females, except for a peak observed only in control females at the end of vitellogenesis. We discuss the functional significance of the observed effects in the context of the putative modes of action of the methanolic plant extract and TFB.

Molecular analysis of nutritional and hormonal regulation of female reproduction in the red flour beetle, Tribolium castaneum

Female reproduction includes maturation of oocytes and the synthesis of yolk proteins (vitellogenin, Vg) in the fat body and their deposition into the oocytes. Our recent studies showed that juvenile hormone (JH) regulates Vg synthesis and 20-hydroxyecdysone (20E) regulates oocyte maturation in the red flour beetle (Tribolium castaneum). Here, we report on the role of nutritional signaling on vitellogenesis and oogenesis. Comparison of gene expression between fed and starved beetles by microarray analysis showed the up-regulation of genes involved in energy homeostasis and down-regulation of genes involved in egg production in the starved beetles. The RNA interference (RNAi) aided knock-down in the expression of genes involved in insulin and TOR signaling pathways showed that both these signaling pathways play key roles in Vg synthesis and oocyte maturation. Starvation of female beetles resulted in a block in Vg synthesis but not in the progression of primary oocyte development to the resting stage. Feeding after starvation induced Vg synthesis and the progression of primary oocytes from the resting stage to the mature stage. However, in the beetles where JH or 20E synthesis or action was blocked by RNAi, both Vg synthesis and oocyte maturation were affected suggesting that both these hormones (JH and 20E) and nutritional signaling and their cross-talk regulate vitellogenesis and oogenesis.

RNA interference of insulin-related peptide and neuroparsins affects vitellogenesis in the desert locust Schistocerca gregaria

The 'classic' insect hormones, juvenile hormone and 20-hydroxyecdysone, can stimulate vitellogenesis and/or ovarian development in adult females of several insect species. Accumulating evidence also indicates a crucial role in female reproductive physiology for peptide hormones, such as insulin-related peptides (IRPs) and neuroparsins (NPs). Especially in dipteran species, IRP signaling has been shown to regulate female reproductive events. The first NP was originally identified from the migratory locust (Locusta migratoria) as an antigonadotropic factor that delayed vitellogenesis. Moreover, NP family members display sequence similarities with the N-terminal domain of vertebrate insulin-like growth factor binding proteins (IGFBPs). In the current study, RNA interference (RNAi) was employed to investigate the possible involvement of IRP and NPs in the control of the female desert locust (Schistocerca gregaria) reproductive system. The cDNAs encoding an IRP (Scg-IRP) and four NPs (Scg-NPs) had previously been cloned from S. gregaria. An RNAi-mediated knock-down of either Scg-NP or Scg-IRP transcript levels was induced in adult female desert locusts and the subsequent effects were analyzed. Knock-down of the Scg-NPs or Scg-IRP affected vitellogenin transcript levels and oocyte growth in a positive and negative way, respectively. The current findings are indicative for a role of Scg-NPs and Scg-IRP in the control of vitellogenin synthesis. A plausible hypothesis is that Scg-IRP may act as a sensor of the nutritional and metabolic status that determines whether vitellogenesis can occur. That the same processes were affected in opposite ways in both RNAi experiments offers an extra argument for antagonizing roles of Scg-NPs and Scg-IRP.

Protein accumulation underlying lifespan extension via ovariectomy in grasshoppers is consistent with the disposable soma hypothesis but is not due to dietary restriction

Reduced reproduction extends lifespan in many experimental animals, but the mechanism by which this occurs is unclear. The disposable soma hypothesis suggests that when reproduction is reduced, more nutrients are allocated to the soma and lifespan is extended. Alternatively, the reproductive tissues or the process of reproduction may have a direct (i.e., non-nutritional) negative effect on lifespan. We used ovariectomized grasshoppers to examine the effects of reduced reproduction throughout the lifespan at the physiological level. We focused on protein, the limiting nutrient for egg production. Ovariectomized females lived significantly longer than sham females. Because both groups ingested similar amounts, the effect was independent of dietary restriction. Despite this, ovariectomized females gained less body mass than sham females. Ovariectomized grasshoppers produced the egg yolk-precursor protein vitellogenin. At the time sham females laid their first clutch, cumulative reproductive protein was similar in ovariectomized and sham females. By advanced ages, however, ovariectomized females had produced about five-fold less cumulative reproductive protein than sham females. In contrast, old ovariectomized females had at least two-fold more hemolymph storage protein. These results are consistent with ovariectomy extending lifespan in part via enhanced protein allocation to storage at the expense of reproduction.

A cumulative feeding threshold required for vitellogenesis can be obviated with juvenile hormone treatment in lubber grasshoppers

Developmental thresholds can ensure that an adequate condition has been attained to proceed through major transitions (e.g. initiation of reproduction, metamorphosis). Nutrition is critical to attaining most thresholds, because it is needed for both growth and storage. Attaining a threshold typically stimulates the release of hormones that commit the animal to the developmental transition, yet the relationships between the nutrition needed for developmental thresholds and these endocrine signals are poorly understood. Lubber grasshoppers require a cumulative feeding threshold to initiate vitellogenesis and potentially commit to oviposition. We tested the relative roles of the nutritional threshold and the major gonadotropin (juvenile hormone; JH) in initiating vitellogenesis and committing to oviposition. The source of JH was removed from all females, and then JH analog was applied after different amounts of feeding. Threshold feeding was not required to initiate vitellogenesis, suggesting that sub-threshold grasshoppers are competent to respond to JH. Further, sub-threshold grasshoppers went on to oviposit earlier than supra-threshold grasshoppers treated with JH at the same time. Hence, threshold feeding is required only to cause the production and release of JH. At the same time, we also found that individuals that were restored with JH late in life tended to favor current reproduction, at the expense of future reproduction. Both time to oviposition and vitellogenin profiles were consistent with this developmental allocation. Taken together, our results suggest that lubber grasshoppers adjust reproductive tactics primarily in response to nutrition (which only serves to release JH) and secondarily in response to age.

Effect of juvenile hormone on vitellogenin gene expression in the fat body of burying beetles, Nicrophorus orbicollis

In the burying beetles, Nicrophorus orbicollis, it is not clear the extent to which synthesis of Vitellogenin (Vg) is under hormonal control. Juvenile hormone (JH) and ovarian development increase rapidly upon discovery of a carcass, the necessary reproductive resource, but in its absence, treatment with JH does not accelerate ovarian development. Here we investigated the effect of manipulating JH titers on Vg gene expression in the fat bodies of newly eclosed and sexually mature females. Topical applications of the JH analogue methoprene at doses of 200, 300, and 400 microg of methoprene/g beetle to newly eclosed females resulted in up to a 5-fold increase in fat body Vg mRNA levels compared to acetone-treated control females. However, none of these increases were statistically significant. We also measured hemolymph Vg in females subjected to prolonged treatment with an intermediate dose of 300 microg of methoprene/g beetle and found no statistically significant increase in hemolymph Vg following treatment. There was, however, a significantly positive correlation between Vg mRNA and hemolymph Vg. Conversely, although injecting sexually mature females with fluvastatin (an inhibitor of JH biosynthesis in the corpora allata) at a dose of 40 microg/ beetle resulted in significantly decreased JH titers in treated females compared to saline-injected controls, Vg transcription rates were not affected. We suggest that in burying beetles, JH alone is not sufficient to upregulate the expression of the Vg genes and that other factors may be involved in regulating their vitellogenic cycle as well.

Plasticity of grasshopper vitellogenin production in response to diet is primarily a result of changes in fat body mass

Life history plasticity is the developmental production of different phenotypes by similar genotypes in response to different environments. Plasticity is common in early post-embryonic or adult development. Later in the developmental stage, the transition from developmentally plastic to canalized (i.e., inflexible) phases is often associated with the attainment of a threshold level of storage. Thresholds are often described simply as total body mass or cumulative consumption of food. The physiological characteristics of thresholds, such as the contributions of the growth of particular organs or the production rate of proteins, are largely unstudied. To address the physiology underlying a threshold-induced developmental transition, total vitellogenin production in response to diet quality in the lubber grasshopper was studied. For individuals that differed in age or dietary protein, somatic mass, ovarian mass, fat body mass, mass-specific vitellogenin production, vitellogenin titer, and storage protein titer were measured. Age and diet strongly affected these parameters, with ovarian mass and fat body mass contributing most to the differences. During mid vitellogenesis, females were highly plastic in response to changing food quality. Only during late vitellogenesis were females unresponsive to changes in food quality. Fat body mass was a more important component of plasticity than was mass-specific vitellogenin production. Because these two variables together make up total vitellogenin production, the greater contribution of fat body mass than mass-specific vitellogenin production suggests that growth factors may be more important than tissue stimulators in producing developmental changes in total vitellogenin production. To our knowledge, this is the first study to demonstrate that mass gain of an organ is more important to developmental plasticity than is the output of that same organ.