EFFECT OF DIETARY PROTEIN AND CARBOHYDRATE LEVELS ON WEIGHT GAIN AND GONAD PRODUCTION IN THE SEA URCHIN LYTECHINUS VARIEGATUS

Ingestion of contaminated kelps by the herbivore Tetrapygus niger: Negative effects on food intake, growth, fertility, and early development

Macrocystis pyrifera reaches distant areas after detachment, accumulate heavy metals, and serve as trophic subsidy. In this context, effects on both adults and larvae of Tetrapygus niger fed with polluted kelps were determined by assessing growth, fertility, and early larval development. Results revealed that sea urchins fed with polluted kelps from highly impacted zone (HIZ) showed a lower growth (3.6% gained weight) and gamete release (358 cells mL^-1) than those fed with non-impacted kelps (NIZ) (19.3% and 945 cells mL^-1). The HIZ treatment showed a developmental delay in comparison to NIZ, accounted mainly by the abundance of malformed 2-arm pluteus larvae (10-15%) during most of the culture. Malformed 4-arm pluteus larvae showed a constant increase, reaching 37% at the end of the culture. Thus, the pollutants ingested by sea urchins can be transferred to their offspring and cause negative effects in their early development, categorizing M. pyrifera as a pollutant carrier.

Alternative Animal Models of Aging Research

Most research on mechanisms of aging is being conducted in a very limited number of classical model species, i.e., laboratory mouse (Mus musculus), rat (Rattus norvegicus domestica), the common fruit fly (Drosophila melanogaster) and roundworm (Caenorhabditis elegans). The obvious advantages of using these models are access to resources such as strains with known genetic properties, high-quality genomic and transcriptomic sequencing data, versatile experimental manipulation capabilities including well-established genome editing tools, as well as extensive experience in husbandry. However, this approach may introduce interpretation biases due to the specific characteristics of the investigated species, which may lead to inappropriate, or even false, generalization. For example, it is still unclear to what extent knowledge of aging mechanisms gained in short-lived model organisms is transferable to long-lived species such as humans. In addition, other specific adaptations favoring a long and healthy life from the immense evolutionary toolbox may be entirely missed. In this review, we summarize the specific characteristics of emerging animal models that have attracted the attention of gerontologists, we provide an overview of the available data and resources related to these models, and we summarize important insights gained from them in recent years. The models presented include short-lived ones such as killifish (Nothobranchius furzeri), long-lived ones such as primates (Callithrix jacchus, Cebus imitator, Macaca mulatta), bathyergid mole-rats (Heterocephalus glaber, Fukomys spp.), bats (Myotis spp.), birds, olms (Proteus anguinus), turtles, greenland sharks, bivalves (Arctica islandica), and potentially non-aging ones such as Hydra and Planaria.

Effects of Dietary Carbohydrate on Weight Gain and Gonad Production in Small Sea Urchins, Lytechinus variegatus

In experiment 1, juvenile sea urchins (n = 80, 0.088 ± 0.001 g wet weight and 5.72 ± 0.04 mm diameter) were held individually and fed ad libitum one of three semi-purified formulated diets (n = 16 individuals treatment-1). In the diets, protein was held constant (310g kg-1 dry, as fed) and carbohydrate level varied (190, 260, or 380 g kg-1 dry, as fed). Wet weights were measured every 2 weeks. Total wet weight gain was inversely proportional to dietary carbohydrate level and energy content of the respective diet. In experiment 2, sea urchins (5.60 ± 0.48g wet weight, n= 40) fed 190 g kg-1 carbohydrate consumed significantly more dry feed than those fed 260 g kg-1, but not more than those fed 380 g kg-1 carbohydrate. Based on differential feed intake rates, sea urchins that consumed more feed also consumed higher levels of protein and had the highest weight gain. Consequently, protein content and/or protein: energy ratio may be important in determining feed utilization and growth among sea urchins in this study. The average digestible energy intake was approximately 70 kcal kg-1 body weight day-1, suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.

PRODUCTION AND ECONOMIC OPTIMIZATION OF DIETARY PROTEIN AND CARBOHYDRATE IN THE CULTURE OF JUVENILE SEA URCHIN Lytechinus variegatus

Juvenile Lytechinus variegatus (ca. 3.95± 0.54 g) were fed one of 10 formulated diets with different protein (ranging from 11- 43%) and carbohydrate (12 or 18%; brackets determined from previous studies) levels. Urchins (n= 16 per treatment) were fed a daily sub-satiation ration equivalent to 2.0% of average body weight for 10 weeks. Our objective was (1) to create predictive models of growth, production and efficiency outcomes and (2) to generate economic analysis models in relation to these dietary outcomes for juvenile L. variegatus held in culture. At dietary protein levels below ca. 30%, models for most growth and production outcomes predicted increased rates of growth and production among urchins fed diets containing 18% dietary carbohydrate levels as compared to urchins fed diets containing 12% dietary carbohydrate. For most outcomes, growth and production was predicted to increase with increasing level of dietary protein up to ca. 30%, after which, no further increase in growth and production were predicted. Likewise, dry matter production efficiency was predicted to increase with increasing protein level up to ca. 30%, with urchins fed diets with 18% carbohydrate exhibiting greater efficiency than those fed diets with 12% carbohydrate. The energetic cost of dry matter production was optimal at protein levels less than those required for maximal weight gain and gonad production, suggesting an increased energetic cost (decreased energy efficiency) is required to increase gonad production relative to somatic growth. Economic analysis models predict when cost of feed ingredients are low, the lowest cost per gram of wet weight gain will occur at 18% dietary carbohydrate and ca. 25- 30% dietary protein. In contrast, lowest cost per gram of wet weight gain will occur at 12% dietary carbohydrate and ca. 35- 40% dietary protein when feed ingredient costs are high or average. For both 18 and 12% levels of dietary carbohydrate, cost per gram of wet weight gain is predicted to be maximized at low dietary protein levels, regardless of feed ingredient costs. These models will compare dietary requirements and growth outcomes in relation to economic costs and provide insight for future commercialization of sea urchin aquaculture.

Relação proteína:carboidrato no desempenho e metabolismo de juvenis de pacamã (Lophiosilurus alexandri)

Objetivou-se neste estudo verificar o melhor nível de inclusão entre proteína e carboidrato no desempenho e algumas respostas metabólicas em juvenis de pacamã (Lophiosilurus alexandri). Testaram-se quatro dietas com as relações proteína/carboidrato (PB:CHO) 1,24; 0,84; 0,51 e 0,33 durante 60 dias. Foram utilizados 240 juvenis de pacamã pesando inicialmente 1,90g, alimentados duas vezes ao dia (8% da biomassa). Avaliou-se o ganho de peso total, taxa de crescimento específico, consumo de ração aparente, conversão alimentar aparente, rendimento de carcaça e gordura visceral. Glicemia, aminoácidos totais livres no plasma e glicogênio hepático também foram avaliados. A relação PB:CHO influenciou (P<0,05) os parâmetros de desempenho e metabolismo, exceto o glicogênio hepático. Maiores concentrações de glicose e aminoácidos totais livres no plasma foram observadas nos peixes que se alimentaram com a dieta contendo a maior relação PB:CHO (1,24). Além disso, observaram-se melhores médias de ganho de peso, taxa de crescimento específico e conversão alimentar aparente. Maiores percentuais de gordura visceral e menor rendimento de carcaça foram observados nos animais submetidos à dieta composta pela menor relação PB:CHO (0,33). Pode-se concluir que a dieta com a relação PB:CHO de 1,24 promoveu melhor desempenho e respostas metabólicas em juvenis de pacamã.

Growth rates are related to production efficiencies in juveniles of the sea urchin Lytechinus variegatus

Growth rates of newly-metamorphosed urchins from a single spawning event (three males and three females) were highly variable, despite being held en masse under identical environmental and nutritional conditions. As individuals reached ~5 mm diameter (0.07-0.10 g wet weight), they were placed in growth trials (23 dietary treatments containing various nutrient profiles). Elapsed time from the first individual entering the growth trials to the last individual entering was 121 days (N = 170 individuals). During the five-week growth trials, urchins were held individually and proffered a limiting ration to evaluate growth rate and production efficiency. Growth rates among individuals within each dietary treatment remained highly variable. Across all dietary treatments, individuals with an initially high growth rate (entering the study first) continued to grow at a faster rate than those with an initially low growth rate (entering the study at a later date), regardless of feed intake. Wet weight gain (ranging from 0.13 -3.19 g, P < 0.0001, R2 = 0.5801) and dry matter production efficiency (ranging from 25.2-180.5%, P = 0.0003, R2 = 0.6162) were negatively correlated with stocking date, regardless of dietary treatment. Although canalization of growth rate during en masse early post-metamorphic growth is possible, we hypothesize that intrinsic differences in growth rates are, in part, the result of differences (possibly genetic) in production efficiencies of individual Lytechinus variegatus. That is, some sea urchins are more efficient in converting feed to biomass. We further hypothesize that this variation may have evolved as an adaptive response to selective pressure related to food availability.

EFFECT OF DIET QUALITY ON NUTRIENT ALLOCATION TO THE TEST AND ARISTOTLE'S LANTERN IN THE SEA URCHIN LYTECHINUS VARIEGATUS (LAMARCK, 1816)

Small adult (19.50 ± 2.01g wet weight) Lytechinus variegatus were fed eight formulated diets with different protein (12 to 36% dry weight as fed) and carbohydrate (21 to 39 % dry weight) levels. Each sea urchin (n = 8 per treatment) was fed a daily ration of 1.5% of the average body weight of all individuals for 9 weeks. Akaike information criterion scores were used to compare six different dietary composition hypotheses for eight growth measurements. For each physical growth response, different mathematical models representing a priori hypotheses were compared using the Akaike Information Criterion (AIC) score. The AIC is one of many information-theoretic approaches that allows for direct comparison of non-nested models with varying number of parameters. Dietary protein level and protein: energy ratio were the best models for prediction of test diameter increase. Dietary protein level was the best model of test with spines wet weight gain and test with spines dry matter production. When the Aristotle's lantern was corrected for size of the test, there was an inverse relationship with dietary protein level. Log transformed lantern to test with spines index was also best associated with the dietary protein model. Dietary carbohydrate level was a poor predictor for growth parameters. However, the protein × carbohydrate interaction model was the best model of organic content (% dry weight) of the test without spines. These data suggest that there is a differential allocation of resources when dietary protein is limiting and the test with spines, but not the Aristotle's lantern, is affected by availability of dietary nutrients.