Victoria K. Gibbs

Effect of Diet Quality on Nutrient Allocation to the Test and Aristotle's Lantern in the Sea Urchin Lytechinus variegatus (LAMARCK, 1816)

ABSTRACT Small, adult (19.50 ± 2.01g wet weight) Lytechinus variegatus (Lamarck, 1816) were fed 8 formulated diets with different protein (12–36% dry weight as fed) and carbohydrate (21–39% 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 wk. Akaike information criterion (AIC) scores were used to compare 6 different dietary composition hypotheses for 8 growth measurements. For each physical growth response, different mathematical models representing a priori hypotheses were compared using the AIC score. The AIC is one of many information—theoretical approaches that allows for direct comparison of nonnested models with varying numbers 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 Aristotles 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 (percent 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, but not the Aristotles lantern, is affected by availability of dietary nutrients.

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.

Nutrition and energetics in rodent longevity research

The impact of calorie amount on aging has been extensively described; however, variation over time and among laboratories in animal diet, housing condition, and strains complicates discerning the true influence of calories (energy) versus nutrients on lifespan. Within the dietary restriction field, single macronutrient manipulations have historically been researched as a means to reduce calories while maintaining adequate levels of essential nutrients. Recent reports of nutritional geometry, including rodent models, highlight the impact macronutrients have on whole organismal aging outcomes. However, other environmental factors (e.g., ambient temperature) may alter nutrient preferences and requirements revealing context specific outcomes. Herein we highlight factors that influence the energetic and nutrient demands of organisms which oftentimes have underappreciated impacts on clarifying interventional effects on health and longevity in aging studies and subsequent translation to improve the human condition.

Dietary Copper Affects Survival, Growth, and Reproduction in the Sea Urchin Lytechinus variegatus

ABSTRACT Copper is an essential micronutrient in the diets of animals. It is a component of many enzymes involved in energy production, participates in immune function, and protects cells from free radicals. However, excessive levels in the diet can be toxic. Small (∼13 g wet weight) Lytechinus variegatus were fed formulated feeds with 12, 36, or 114 mg Cu/kg for 12 wk (levels based on established dietary levels for other marine invertebrates, supplemented as CuSO4·5H2O). Under these experimental conditions, wet weights of individuals fed a 36-mg Cu/kg diet were slightly higher (43.2 ± 1.2 g (SEM); P = 0.069) than those fed a 12mg Cu/kg and 114-mg Cu/kg diet (39.9 ± 1.2 and 40.3 ± 1.7 g wet weight, respectively). Ovary and gut wet weights were significantly lower (P < 0.003) in the 114-mg Cu/kg diet than the 12-mg Cu/kg and 36-mg Cu/kg diets (7.24 ± 0.75 g, 8.11 ± 0.55 g, and 4.99 ± 0.32 g ovary wet weight and 0.97 ± 0.04 g, 1.07 ± 0.06 g, and 0.83 ± 0.04 g gut wet weight for the 12-, 36-, and 114-mg Cu/kg diets, respectively). Mature gamete formation in ovary and testis was inversely correlated with dietary copper level. Acini from the ovaries and testis of urchins in the 36-mg Cu/kg and 114-mg Cu/kg diet treatments had a greater area occupied by nutrient phagocytes than urchins on the 12-mg Cu/kg diet. In diets containing low dietary copper (12 mg Cu/kg), survivorship decreased from 100% to 87%. These data suggest that dietary copper is essential for normal physiological function but can be detrimental for certain physiological processes at high levels. This information will help in the development of formulated feeds for sea urchin aquaculture.