Late Juvenile Stages Research Articles

Life history of the stem tetrapod Acanthostega revealed by synchrotron microtomography

The transition from fish to tetrapod was arguably the most radical series of adaptive shifts in vertebrate evolutionary history. Data are accumulating rapidly for most aspects of these events1–5, but the life histories of the earliest tetrapods remain completely unknown, leaving a major gap in our understanding of these organisms as living animals. Symptomatic of this problem is the unspoken assumption that the largest known Devonian tetrapod fossils represent adult individuals. Here we present the first life history data for a Devonian tetrapod, from the Acanthostega mass-death deposit of Stensiö Bjerg, East Greenland6,7. Using propagation phase contrast synchrotron microtomography (PPC-SRµCT)8 to visualize the histology of humeri (upper arm bones) and infer their growth histories, we show that even the largest individuals from this deposit are juveniles. A long early juvenile stage with unossified limb bones, during which the individual grew to almost final size, was followed by a slow-growing late juvenile stage with ossified limbs which lasted at least six years in some individuals. The late onset of limb ossification suggests that the juveniles were exclusively aquatic, and the predominance of juveniles in the sample suggests segregated distributions of juveniles and adults at least at certain times. The absolute size at which limb ossification began differs greatly between individuals, suggesting the possibility of sexual dimorphism, adaptive strategies or competition-related size variation.

Habitat-specific growth, survival and diet of late juvenile hatchery-reared spotted seatrout (Cynoscion nebulosus)

As a key recreational fishery species throughout the Gulf of Mexico, the spotted seatrout (Cynoscion nebulosus Cuvier) requires sound management practices (VanderKooy and Muller, 2003; Fulford and Hendon, 2010). Accordingly, it is imperative to fully understand the ecology of spotted seatrout (Lorio and Perret, 1978), especially factors affecting the successful recruitment of this estuarine-dependent carnivore. Considering the large gap in knowledge about the ecology of late juvenile stage spotted seatrout, as well as the need to evaluate current stock enhancement practices for this species, the objective of this study was to assess the growth, survival and diet of late juvenile hatchery-reared (HR) spotted seatrout within three prospective nursery habitats in a shallow bay system: submerged aquatic vegetation (SAV), non-vegetated shoreline (NVS), and non-vegetated open water (NVO). While caged under natural conditions for 4weeks, relative growth was significantly greater for fish caged in SAV and NVS habitats compared to NVO habitat. Mortality was relatively high in the first week of the study during acclimation. Stomachs of HR fish contained prey, and the diet composition of HR fish included common prey types consumed by comparable sizes of wild fish. Findings indicate that habitats within or in close proximity to SAV or marsh shoreline offer more favorable conditions than deeper open water habitat for late juvenile HR spotted seatrout. Moreover, HR fish can acclimate to natural conditions and successfully transition to a natural diet, in the absence of predators and competitors.

New Material of the Pterosaur Gladocephaloideus Lü et al., 2012 from the Early Cretaceous of Liaoning Province, China, with Comments on Its Systematic Position.

Although there are nine genera of ctenochasmatoids reported from the Jehol Biota, at present each is known from a specimen that has either a skull or a relatively complete postcranial skeleton. A nearly complete juvenile specimen of Gladocephaloideus from the Lower Cretaceous Jiufotang Formation of Sihedang, Lingyuan of Liaoning Province is the most complete ctenochasmatoid preserved to date with a skull and postcranial skeleton. Based on the holotype (IG-CAGS 08–07) and the nearly complete new specimen (JPM 2014–004), the diagnosis of Gladocephaloideus is amended: approximately 50 teeth in total with sharp tips; small nasoantorbital opening, occupying approximately 13% of total skull length; ratio of prenarial rostrum length to skull length approximately 0.63; deep groove along the mid-line of the mandibular symphysis; length to width ratio of the longest cervical vertebra = 4.1; ratio of femur length to tibia length = 0.61; tibia as long as the wing-phalange 1. Phylogenetic analysis recovers Gladocephaloideus within the clade Ctenochasmatidae. Gladocephaloideus has a closer relationship to the Chinese Pterofiltrus rather than to other ctenochasmatid pterosaurs. Microstructure of limb bones implies that JPM 2014–004 represents an early juvenile of Gladocephaloideus jingangshanensis, and that the type specimen is not a fully grown specimen either. We assume that the holotype may equate to the late juvenile or sub-adult developmental stage of Gladocephaloideus.

Compilation of Japanese fisheries statistics for the Japanese eel, Anguilla japonica, since 1894: a historical dataset for stock assessment

AbstractFishery sustainability and the extinction risk of the Japanese eel, Anguilla japonica, are of global concern. The landings of the Japanese eel in Japan comprise a large part of the landings in East Asia. This study provides a compiled dataset of the annual fisheries statistics of the Japanese eel in Japan for stock assessment. The Japanese government has been recording Japanese eel statistics annually since 1984 in five series of annual reports by conducting systematic questionnaire surveys of fisheries managers and associations; however, most of these data are stored in analog format. The key variables in the dataset include the harvest weight of eels, the harvest weight and number of seeds for aquaculture, the number of eels stocked, and the number of management entities engaged in the eel fishery. The levels of spatial aggregation of the variables include the site (river and lake), prefecture, inland and coastal waters, and total in Japan. We also incorporated location data (latitude and longitude) of the site and prefecture into the dataset. Eel harvest includes primarily yellow eels (late juvenile stage) and silver eels (mature stage). Seed harvest in inland waters includes glass eels (intermediate stage between leptocephalus and elver) and elvers (early juvenile stage). Seed harvest from coastal waters comprises glass eels. This dataset provides information to assess long‐term trends in the Japanese eel population.

Effects of food restriction across stages of juvenile and early adult development on body weight, survival and adult life history.

Organisms have to allocate limited resources among multiple life-history traits, which can result in physiological trade-offs, and variation in environmental conditions experienced during ontogeny can influence reproduction later in life. Food restriction may lead to an adaptive reallocation of the limited resources among traits as a phenotypically plastic adjustment, or it can act as an overall constraint with detrimental effects throughout reproductive life. In this study, we investigated experimentally the effects of food restriction during different stages of the juvenile and early adult development on body weight, survival and reproductive success in females and males of the European earwig Forficula auricularia. Individuals either received limited or unlimited access to food across three different stages of development (fully crossed) allowing us to identify sensitive periods during development and to test both additive and interactive effects of food limitation across stages on development and reproduction. Food restriction during the early and late juvenile stage had additive negative effects on juvenile survival and adult body weight. With regard to reproductive success of females which produce up to two clutches in their lifetime, restriction specifically in the late juvenile stage led to smaller first and second clutch size, lower probability of second clutch production and reduced hatching success in the second clutch. Reproductive success of females was not significantly affected when their male mates experienced food restriction during their development. Our findings in general support the 'silver-spoon' hypothesis in that food restriction during juvenile development poses constraints on development and reproduction throughout life.

Dietary overlap among early juvenile stages in an Antarctic notothenioid fish assemblage at Potter Cove, South Shetland Islands

To date, studies of food overlap in Antarctic fish have been performed on a mixture of late juvenile and adult stages, leaving the young immature specimens (TL ≤ 10 cm) practically unexplored. We studied diet overlap and potential competition among early juvenile individuals in a coastal notothenioid community at Potter Cove, by analysing the stomach contents of 225 fish of 5 species collected in the summer of 2009–2010. We used frequency of occurrence (F %) and the coefficient “Q” for diet evaluation and the method of Tyler and the similarity index “S” for food overlap. Amphipods of the suborder Gammaridea were the main (Q > 2.900) and most frequent (% F) prey for all species, although Notothenia coriiceps also consumed gastropods of the family Littorinidae, mostly Laevilitorina antarctica. Secondary prey were algae for Notothenia rossii and N. coriiceps, calanoid (pelagic) and harpacticoid (benthic) copepods for Trematomus newnesi and the latter copepods and isopods of the family Munnidae for Lepidonotothen nudifrons. The reoccurrence of prey among fish species was 39.6 % and food overlap between 90 % of species pairs was under 58 %. Because similarly low values of diet overlap were reported for intermediate/advanced juveniles and adults of the same species at the same site, we conclude that there is no difference in the degree of interspecific food overlap and therefore potential competition between the immature and mature fraction of the fish community. Food competition is avoided by resource partitioning along a depth gradient or by different prey species.

Metabolic acceleration in animal ontogeny: An evolutionary perspective

Acceleration of metabolism is defined as a long-term increase of respiration, that is faster than the typical trajectory during the life cycle of an individual, from embryo to adult. The Dynamic Energy Budget (DEB) model is used to quantify the typical trajectory. All DEB parameters were estimated for over 300 animal species from most large phyla and all chordate classes. The goodness of fit is generally excellent, including embryo development (embryo weight, respiration, amount of yolk). Although many species match predictions for metabolic rates, particular taxa, including all those with larval development, but also ones with less clear larval stages, deviated and have a lower metabolic rate as embryo, compared to late juvenile and adult stages: they accelerate their metabolism during the life cycle. Five different types of acceleration are identified, examples are given, and methods are presented to recognise these different types. Associated life history traits are discussed in an evolutionary and ecological context. Arguments are presented for why accelerating species have an extra slow start of metabolism and why parental care evolved in endotherms.

Dispersal‐mediated effect of microhabitat availability and density dependence determine population dynamics of a forest floor web spider

Landscapes in nature can be viewed as a continuum of small total habitable area with high fragmentation to widely spreading habitats. The dispersal-mediated rescue effect predominates in the former landscapes, while classical density-dependent processes generally prevail in widely spread habitats. A similar principle should be applied to populations of organisms utilizing microhabitats in limited supply. To test this hypothesis, we examined the population dynamics of a web spider, Neriene brongersmai, in 16 populations with varying degrees of microhabitat availability, and we explored whether: (i) high microhabitat availability improves survival rate during density-independent movement, while the resultant high density reduces survival rate in a density-dependent manner; and (ii) temporal population stability increases with microhabitat availability at the population level. Furthermore, we conducted two types of field experiments to verify whether high microhabitat availability actually reduces mortality associated with web-site movement. Field observations revealed that demographic change in N.brongersmai populations was affected by three factors at different stages, namely the microhabitat limitation from the early to late juvenile stages, the density dependence from the late juvenile to adult stages and the food limitation from the adult to the next early juvenile stages. In addition, there was a tendency for a positive association between population stability and microhabitat availability at the population level. A small-scale experiment, where the frequency of spider web relocation was equalized artificially, revealed that high microhabitat availability elevated the survival rate during a movement event between web-sites. The larger spatiotemporal scale experiment also revealed an improved spider survival rate following treatment with high microhabitat availability, even though spider density was kept at a relatively low level. The population dynamics of N.brongersmai can be determined primarily by density-independent processes based on web-site fragmentation and density-dependent processes driven by interference competition. We conclude that depending on the amount of habitat resources, the relative importance of the two contrasting paradigms-equilibrium and non-equilibrium-appears to vary, even within a particular system.

An immunocytochemical window into the development of Platynereis massiliensis (Annelida, Nereididae).

The nereidid annelid Platynereis dumerilii emerged as a well-understood model organism. P. dumerilii and P. massiliensis are sister taxa, which are morphologically indistinguishable as adults. Interestingly, they exhibit highly contrasting life-histories: while P. dumerilii is a gonochorostic species with planktonic feeding larvae, P. massiliensis is a protandric hermaphrodite with lecitotrophic semi-direct -development in brood tubes. Using light microscopy and immunohistochemical methods coupled with confocal laser scanning microscopy, we describe the development of P. massiliensis. Musculature was stained with phalloidin-rhodamine. FMRFamide, acetylated α-tubulin, and serotonin were targeted by antibodies for the staining of neuronal structures. Additionally, eye development was investigated with the specific 22C10-antibody. The development of P. massiliensis is characterized by the absence of a free-swimming stage, a late development of food uptake, and the presence of a large amount of yolk even in late juvenile stages. Most notably, early juvenile stages already exhibit an organization of several organ systems that resembles those of adults. Larval characters present in the free-swimming feeding larvae of P. dumerilii, as e.g. the apical organ and larval eyes, are absent and regarded to be lost in developing stages of P. massiliensis. Many of the differences found in the development of these two species can be described in the context of heterochronic changes. We strongly advocate expanding evolutionary developmental studies from the well-established model annelid P. dumerilii to the closely related P. massiliensis to study the evolutionary conservation and divergence of genetic pathways involved in developmental processes.

Alimentación y ontogenia trófica alimentar de juveniles de characiformes en bancos de macrófitas acuáticas en el río Solimões/Amazonas

El ambiente de macrófitas acuáticas desempeña un importante papel como sítio de alimentación de peces juveniles del Orden Characiformes en la várzea de la Amazonia Central. En el presente trabajo fueron evaluadas las variaciones ontogenéticas en la dieta, en función del aumento corporal de juveniles de Brycon amazonicus, Triportheus angulatus, Mylossoma duriventre y Semaprochilodus insignis recolectados en bancos de macrófitas en un trecho del río Solimões/Amazonas. Fueron analizados 1.181 ejemplares, los especímenes fueron divididos arbitrariamente en tres clases de desarrollo de acuerdo con la longitud estándar (CP): clase I (15-30 mm), clase II (31-45 mm) y clase III (46-60 mm). Para el análisis de la dieta fue calculado el Índice Alimentar (IAi), combinando los métodos de frecuencia de ocurrencia y volumen relativo. Fueron observadas variaciones ontogenéticas en la dieta de M. duriventre y de T. angulatus durante la fase juvenil. Todas las especies muestreadas poseen forrajeo selectivo y llegan al fin de la fase juvenil con comportamiento trófico semejante al que presentan en la fase adulta.

Wood Frogs Population in a Changing Environment

We present new results for a mathematical model for the dynamics of a population of Wood Frogs, which continue the investigation begun in [1]. The model is in the form of a system of nonlinear impulsive differential equations for each developmental stage (larvae, juvenile, and mature). It also takes into account the differences in the growth of the early, middle, and late juvenile stages. We describe numerical simulations for the study of the environmental impact on the population, in particular we investigate three issues: the existence of periodic solutions for the model; the recovery of the population from 1-3 dry years in which no larvae hatch; and the dependence of the model on the system parameters. It is seen that the results agree qualitatively with the observed data, which allows us to use the model for a tentative prediction of next years development. We also present some additional mathematical and numerical issues for future study. [1] N. Al-Asuoad, R. Anguelov, K. Berven, M. Shillor, Model and Simulations of a Wood Frog Population, Biomath 1 (2012), 1209032, http://dx.doi.org/10.11145/j.biomath.2012.09.032

Dactylella oviparasitica parasitism of the sugar beet cyst nematode observed in trixenic culture plates

The nematophagous fungus Dactylella oviparasitica is considered the primary cause of a sugar beet cyst nematode (Heterodera schachtii) population suppression in a field at the Agricultural Operations, University of California, Riverside. Parasitism of H. schachtii by the ascomycete D. oviparasitica was studied using both Arabidopsis thaliana (type Landsberg erecta) and cabbage as host plants in gnotobiotic agar culture. Suitability of Arabidopsis as a host for H. schachtii was confirmed using seedlings grown with the nematode in axenic sand culture. Both developing males and females of H. schachtii broke through the Arabidopsis root surface during late juvenile stages and both were susceptible to D. oviparasitica parasitism. In contrast to Arabidopsis, developing juvenile males remained in nearly all observed cases enclosed within the cabbage root tissues while the larger body expansion of the female juveniles caused the root cortex to split; consequently only the latter ones were accessible to the fungus. In the presence of D. oviparasitica, the number of females with eggs was reduced by more than 95% and the number of eggs per female by almost 60% as compared to females developing on plates without the fungus. Viable eggs were not susceptible to parasitism while more than 90% of heat- or cold-killed eggs were rendered susceptible. These observations suggest that parasitism of developing juveniles may be the essential mode of action in the population suppression of H. schachtii.

Skeletal development inPan paniscuswith comparisons toPan troglodytes

Fusion of skeletal elements provides markers for timing of growth and is one component of a chimpanzee's physical development. Epiphyseal closure defines bone growth and signals a mature skeleton. Most of what we know about timing of development in chimpanzees derives from dental studies on Pan troglodytes. Much less is known about the sister species, Pan paniscus, with few in captivity and a wild range restricted to central Africa. Here, we report on the timing of skeletal fusion for female captive P. paniscus (n = 5) whose known ages range from 0.83 to age 11.68 years. Observations on the skeletons were made after the individuals were dissected and bones cleaned. Comparisons with 10 female captive P. troglodytes confirm a generally uniform pattern in the sequence of skeletal fusion in the two captive species. We also compared the P. paniscus to a sample of three unknown-aged female wild P. paniscus, and 10 female wild P. troglodytes of known age from the Taï National Park, Côte d'Ivoire. The sequence of teeth emergence to bone fusion is generally consistent between the two species, with slight variations in late juvenile and subadult stages. The direct-age comparisons show that skeletal growth in captive P. paniscus is accelerated compared with both captive and wild P. troglodytes populations. The skeletal data combined with dental stages have implications for estimating the life stage of immature skeletal materials of wild P. paniscus and for more broadly comparing the skeletal growth rates among captive and wild chimpanzees (Pan), Homo sapiens, and fossil hominins.

Hypothalamic Actions and Interactions of Alcohol and IGF-1 on the Expression of Glial Receptor Protein Tyrosine Phosphatase-β During Female Pubertal Development

Hypothalamic glial-neuronal communications are important for the activation of luteinizing hormone releasing hormone (LHRH) secretion at the time of puberty. As we have shown that alcohol (ALC) diminishes prepubertal LHRH secretion and delays puberty, we first assessed the effects of short-term ALC administration on the basal expression of a specific gene family involved in glial-neuronal communications. Second, as insulin-like growth factor-1 (IGF-1) is a critical regulator of LHRH secretion and the pubertal process, we then assessed whether IGF-1 could induce the expression of these signaling genes and determine whether ALC can block this affect. Immature female rats were fed a liquid diet containing ALC for 6 days beginning when 27 days old. Control animals received either the companion isocaloric liquid diet or rat chow and water. Animals were decapitated on day 33, in the late juvenile stage of development. Medial basal hypothalamic (MBH) tissues were obtained for gene and protein analyses of glial receptor protein tyrosine phosphatase-β (RPTPβ) and the 2 neuronal components, contactin and contactin-associated protein 1 (Caspr1). In the second experiment, IGF-1 was administered into the third ventricle (3V) and the MBH removed 6 hours after peptide delivery, and the above-mentioned 3 genes were analyzed by real-time PCR. To determine whether this action was affected by ALC, immature female rats were administered either ALC (3 g/kg) or water via gastric gavage at 0900 hours. At 1030 hours, the ALC and control groups were subdivided such that half of the animals were injected into the 3V with IGF-1 and the other half with an equal volume of saline. Rats were killed 6 hours after the IGF-1 injection and MBHs collected. Real-time PCR showed that when compared with control animals, ALC caused a marked decrease (p < 0.001) in the basal expression of the RPTPβ gene, but did not affect the expression of either contactin or Caspr1. Likewise, analysis by Western blotting demonstrated that ALC caused suppressed (p < 0.001) levels of the RPTPβ protein, with the expressions of both contactin and Caspr1 proteins being unaltered. In the second experiment, results showed that only the RPTPβ gene was stimulated (p < 0.05) by IGF-1 in the MBH 6 hours after peptide delivery. Assessments revealed that the IGF-1 induced increase (p < 0.01) in the expression of the RPTPβ gene was blocked by the presence of ALC. Prepubertal ALC exposure is capable of interfering with hypothalamic glial-neuronal communications by suppressing the synthesis of the glial product, RPTPβ, which is required for binding to the contactin-Caspr1 complex on LHRH neuronal terminals, thus suggesting that this action of ALC contributes to its detrimental effects on the pubertal process.

Prepubertal ethanol exposure alters hypothalamic transforming growth factor-α and erbB1 receptor signaling in the female rat

Glial-derived transforming growth factor alpha (TGFα) activates the erbB1/erbB2 receptor complex on adjacent glial cells in the medial basal hypothalamus (MBH). This receptor activation stimulates the synthesis and release of prostaglandin-E 2 (PGE 2) from the glial cells, which then induces the release of prepubertal luteinizing hormone-releasing hormone (LHRH) secretion from nearby nerve terminals; thus, showing the importance of glial–neuronal communications at the time of puberty. Ethanol (EtOH) is known to cause depressed prepubertal LHRH secretion and delayed pubertal development. In this study, we assessed whether short-term EtOH exposure could alter the hypothalamic glial to glial signaling components involved in prepubertal PGE 2 secretion. Immature female rats began receiving control or EtOH diets beginning when 27 days old. The animals were killed by decapitation after 4 and 6 days of treatment and confirmed to be in the late juvenile stage of development. Blood and brain tissues were collected for gene, protein, and hormonal assessments. Real-time polymerase chain reaction (PCR) analysis demonstrated that EtOH did not affect basal levels of erbB1 gene expression in the MBH. Expression of total erbB1 protein was also unaffected; however, the EtOH caused suppressed phosphorylation of erbB1 protein in the MBH at both 4 and 6 days ( P < .01) as revealed by Western blotting. Phosphorylation and total protein levels of erbB2 receptor were not affected by EtOH exposure. Because this receptor is critical for PGE 2 synthesis/release, which mediates the secretion of LHRH, we assessed whether in vivo EtOH exposure could affect the release of PGE 2. EtOH exposure for 6 days suppressed ( P < .01) basal levels of PGE 2 released into the medium. The effects of 4- and 6-day EtOH exposure on gene and protein expressions of TGFα, an upstream component in the activation of erbB1/erbB2, were also studied. The levels of TGFα mRNA were increased markedly at 4 days ( P < .001), but declined to near basal levels by 6 days in the EtOH-treated animals. The EtOH caused increases in TGFα protein expression at both 4 ( P < .001) and 6 ( P < .01) days; hence, suggesting that the EtOH inhibited release of the peptide. We confirmed this inhibition by showing decreased ( P < .01) TGFα released from MBHs incubated in vitro following 6 days of EtOH exposure in vivo. Thus, these results demonstrate that EtOH is capable of interfering with hypothalamic glial to glial signaling processes involved in prepubertal PGE 2 secretion.

Ontogeny of osmoregulation and salinity tolerance in the gilthead sea bream Sparus aurata

The gilthead sea bream, Sparus aurata, is a euryhaline teleost that hatches in the open sea. The larvae drift to the coast and juveniles migrate into estuaries and lagoons where the salinity of the water may vary from brackish to hyper-saline. The ontogeny of osmoregulation in Sparus aurata was studied at successive stages, from day 1 (D1) post-hatch to the late juvenile stage (D300) after exposure to different salinities ranging from fresh water to 45.1‰, at 18 °C. Survival ranged from between 5.1 and 39.1‰ at D3, and from 1.0 to 45.1‰ from D75. The fish were hyper-hypo-osmotic regulators at all studied stages. The acquisition of the full ability to hypo- and hyper-regulate occurred in four steps. The osmoregulatory capacity appeared age-dependent and reached its maximum level after D96, and the localization of ionocytes in the integument and gills occurred concurrently during development of the sea bream. However, the main site of osmoregulation shifted from the integument to the gills from D30 to D70, with a corresponding sharp increase in the osmoregulatory ability. Our results suggest that the early development of osmoregulatory ability, and thus of salinity tolerance in the sea bream may provide an advantageous flexibility for the timing of the migration between sea and estuaries and lagoons.

Growth temperature and plant age influence on nutritional quality of &lt;i&gt;Amaranthus&lt;/i&gt; leaves and seed germination capacity&lt;sup&gt;#&lt;/sup&gt;

As a leafy vegetable, Amaranthus can be harvested at different stages of plant growth, ranging from young seedlings to the late juvenile stage, but data on the changes in leaf nutritional value with plant age are scanty. The objective of this study was to determine the effect of growth temperature on Amaranthus leaf yield and nutritional quality at different stages of plant growth. Five species, A. hybridus var. cruentus, A. hypochondriacus, A. tricolor, A. thunbergii and A. hybridus were compared for their response to hot (33/27oC), warm (27/21oC) and cool (21/15oC) temperature regimes (day/night) in separate glasshouses. Plants were harvested at 20, 40 and 60 d after sowing and leaf yield, minerals (Ca, P and Fe), total protein content, amino acid (methionine and lysine) content and antioxidant activity (inhibition of linoleic acid oxidation) were determined. Seed yield and germination capacity, during two years of after-ripening, were also determined. Results showed that leaf protein content differed significantly (P The phosphorus content of leaves was not significantly affected by temperature and stage of plant development, and there were also no significant differences between species. However, the amounts of both calcium and iron changed significantly (P leaves increased consistently with plant age and there were significant (P < 0.01) differences between stages of plant development and growth temperature. Warm temperature regimes were most favourable (P < 0.01) for biomass accumulation in all species. Seed production under cool and hot temperatures significantly (P < 0.01) decreased seed germination capacity for all species, but germination improved in response to after-ripening. It is recommended that for greater nutritional benefit, Amaranthus should be grown under warm conditions and younger leaves are preferable.

Short‐Term Alcohol Administration Alters KiSS‐1 Gene Expression in the Reproductive Hypothalamus of Prepubertal Female Rats

Kisspeptins bind to the G-protein-coupled receptor (GPR54) to activate hypothalamic luteinizing hormone releasing hormone (LHRH) secretion at the time of puberty. Alcohol (ALC) causes depressed prepubertal LHRH release, resulting in depressed luteinizing hormone (LH) secretion and delayed puberty. Because KiSS-1 and GPR54 are important to the onset of puberty, we assessed the effects of chronic ALC administration on basal expression of these puberty-related genes within the reproductive hypothalamus, as well as hormones and transduction signaling pathways contributing to their activity. Immature female rats were fed a liquid diet containing ALC for 6 days beginning when 27 days old. Controls received either companion isocaloric liquid diet or rat chow and water. Animals were decapitated on day 33, in the late juvenile stage of development. Blood was collected for the assessment of serum hormone levels. Brain tissues containing the anteroventral periventricular (AVPV) and arcuate (ARC) nuclei were obtained for assessing expression of specific puberty-related genes and proteins. KiSS-1 mRNA levels in the AVPV and ARC nuclei were suppressed (p < 0.001) in the ALC-treated rats. GPR54 gene and protein expressions were both modestly increased (p < 0.05) in AVPV nucleus, but not in ARC nucleus. Alcohol exposure also resulted in suppressed serum levels of insulin-like growth factor-1 (IGF-1), LH, and estradiol (E(2)). As IGF-1, in the presence of E(2), can induce expression of the KiSS-1 gene, we assessed the potential for ALC to alter IGF-1 signaling in the reproductive hypothalamus. IGF-1 receptor gene and protein expressions were not altered. However, protein expression of phosphorylated Akt, a transduction signal used by IGF-1, was suppressed in the AVPV (p < 0.05) and ARC (p < 0.01) nuclei. Alcohol causes suppressed KiSS-1 gene expression in the reproductive hypothalamus; hence, contributing to this drug's ability to cause suppressed LHRH secretion and disruption of the pubertal process. We suggest that this action, at least in part, is through altered IGF-1 signaling.

Effect of an herbivorous diet on energy balance of Litopenaeus vannamei at selected ontogenetic stages

Herbivorous (20% vegetable protein, 40% carbohydrate) and carnivorous diets (40% marine animal protein, 20% carbohydrate) were experimentally tested to assess their effect on the energy balance and energetic substrates utilized by postlarvae (PL's /15 days) and juvenile shrimp (3–6 g) of Litopenaeus vannamei. Postlarval stage 60 (PL 60, early juveniles) shrimps fed HeD and CaD diets, then late juveniles (3–6 g) acclimated to the same diets were tested for their respective energy partitioning potential. No significant differences ( p > 0.05) on growth were obtained in early juveniles (mean final wet weight of 0.19 g). However in late juvenile stages a significant difference ( p < 0.05) in growth rate was observed. In terms of energy partitioning, both early and late juveniles seem to spend more energy in respiratory metabolism than in the elimination of excretion products. A change in feed composition based on quality protein sources induced some modifications on shrimp's activity measured by heat increment. Shrimps fed with an herbivorous diet showed a higher heat increment. Interestingly, the early stages of L. vannamei display a remarkable capacity to assimilate a plant protein-based and a high carbohydrate level diet. Such capacity with a stimulation of genes would lead to a good adaptation of juveniles receiving all-plant diets to sustain growth performances up to a marketable size. The implications of these findings for the shrimp farming feeding costs are briefly discussed.

Natural Variation in Larval Size and Developmental Rate of the Northern QuahogMercenaria mercenariaand Associated Effects on Larval and Juvenile Fitness

Larval size and developmental rate can vary tremendously within and among cohorts because of genetics, environment, and maternal investment. This natural variation in larvae may have effects that span multiple life stages. Here we investigate the effects of larval size and developmental stage on the subsequent life stages of the commercially and ecologically important clam Mercenaria mercenaria. Fifteen days after fertilization, we divided larvae into two groups based on their developmental stage (umbonal or pediveliger) and recorded survival, size, and developmental stage of individuals over the next 4 months. Results revealed that after four months larvae that had only reached the umbonal stage by Day 15 were significantly smaller than those that had reached the pediveliger stage. These smaller and less developed larvae were less successful than the larger and more developed larvae across late larval and juvenile stages. In particular, smaller and less developed larvae were less likely to metamorphose, required more time to metamorphosis, and had lower survival and growth rates. These results suggest that natural variation in larval size and developmental rate can affect recruitment in a variety of ways: (1) Increased time to metamorphosis may increase the cost to larvae via predation or exposure to environmental stress, (2) Decreased proportion of larvae able to metamorphose may directly reduce the number of settlers, and (3) Decreased growth and survival rates for juveniles may reduce the number of new recruits. We also discuss the persistence of natural variation in larval size and developmental rate in light of the observed negative effects associated with smaller and less-developed larvae.