An aquatic vertebrate can use amino acids from environmental water

Evidence for transporter-mediated uptake of environmental L-glutamate in a freshwater sponge, Ephydatia muelleri

The freshwater sponge, Ephydatia muelleri, lacks a nervous or endocrine system and yet it exhibits a coordinated whole-body action known as a "sneeze" that can be triggered by exposure to L-glutamate. It is not known how L-glutamate is obtained by E. muelleri in sufficient quantities (i.e., 70 µM) to mediate this response endogenously. The present study tested the hypothesis that L-glutamate can be directly acquired from the environment across the body surface of E. muelleri. We demonstrate carrier mediated uptake of two distinct saturable systems with maximal transport rates (Jmax) of 64.27 ± 4.98 and 25.12 ± 1.87 pmols mg-1 min-1, respectively. The latter system has a higher calculated substrate affinity (Km) of 2.87 ± 0.38 µM compared to the former (8.75 ± 1.00 µM), indicative of distinct systems that can acquire L-glutamate at variable environmental concentrations. Further characterization revealed potential shared pathways of L-glutamate uptake with other negatively charged amino acids, namely D-glutamate and L-aspartate, as well as the neutral amino acid L-alanine. We demonstrate that L-glutamate uptake does not appear to rely on exogenous sodium or proton concentrations as removal of these ions from the bathing media did not significantly alter uptake. Likewise, L-glutamate uptake does not seem to rely on internal proton motive forces driven by VHA as application of 100 nM of the VHA inhibitor bafilomycin did not alter uptake rates within E. muelleri tissues. Whether the acquired amino acid is used to supplement feeding or is stored and accumulated to mediate the sneeze response remains to be determined.

Waterborne amino acids: uptake and functional roles in aquatic animals

Dissolved organic matter is a ubiquitous component of freshwater and marine environments, and includes small nutrient molecules, such as amino acids, which may be available for uptake by aquatic biota. Epithelial transporters, including cotransporters, uniporters and antiporters, facilitate the absorption of dissolved amino acids (often against concentration gradients). Although there is a lack of mechanistic and molecular characterization of such transporters, pathways for the direct uptake of amino acids from the water appear to exist in a wide range of marine phyla, including Porifera, Cnidaria, Platyhelminthes, Brachiopoda, Mollusca, Nemertea, Annelida, Echinodermata, Arthropoda and Chordata. In these animals, absorbed amino acids have several putative roles, including osmoregulation, hypoxia tolerance, shell formation and metabolism. Therefore, amino acids dissolved in the water may play an important, but overlooked, role in aquatic animal nutrition.

Invasive investigation: uptake and transport of l-leucine in the gill epithelium of crustaceans

Many aquatic species are well known as extremely successful invaders. The green crab (Carcinus maenas) is an arthropod native to European waters; however, it is now known to be a globally invasive species. Recently, it was discovered that the C. maenas could transport nutrients in the form of amino acids across their gill from the surrounding environment, a feat previously thought to be impossible in arthropods. We compared the ability for branchial amino acid transport of crustacean's native to Canadian Pacific waters to that of the invasive C. maenas, determining if this was a novel pathway in an extremely successful invasive species, or a shared trait among crustaceans. Active transport of l-leucine was exhibited in C. maenas, Metacarcinus gracilis, Metacarcinus magister, and Cancer productus across their gill epithelia. Carcinus maenas exhibited the highest maximum rate of branchial l-leucine transport at 53.7 ± 6.24 nmolg-1 h-1, over twice the rate of two native Canadian crustaceans. We also examined the influence of feeding, gill specificity, and organ accumulation of l-leucine. Feeding events displayed a heavy influence on the branchial transport rate of amino acids, increasing l-leucine transport rates by up to 10-fold in C. maenas. l-leucine displayed a significantly higher accumulation rate in the gills of C. maenas compared to the rest of the body at 4.15 ± 0.78 nmolg-1 h-1, with the stomach, hepatopancreas, eyestalks, muscle tissue, carapace and heart muscle exhibiting accumulation under 0.15 nmolg-1 h-1. For the first time, the novel transport of amino acids in Canadian native arthropods is described, suggesting that branchial amino acid transport is a shared trait among arthropods, contrary to existing literature. Further investigation is required to determine the influence of environmental temperature and salinity on transport in each species to outline any competitive advantages of the invasive C. maenas in a fluctuating estuarine environment.

Growth-Promotion Effects of Dissolved Amino Acids in Three Species of Hynobius Salamander Hatchlings

It has been suggested that aquatic vertebrates may be able to meet their energy requirements by using the amino acids dissolved in environmental water. If this ability can be applied to aquatic organisms generally, then conventional ecological theories related to food web interactions should be revisited, as this would likely bring about significant advances in applications. Here, we prepared two 1 mM amino acid (phenylalanine and glycine) solutions in environmental water and conducted laboratory experiments to demonstrate the utilization of dissolved amino acids by hatchlings of three salamander species (Ezo: Hynobius retardatus, Tohoku: Hynobius lichenatus, and Japanese black: Hynobius nigrescens). Compared to controls (no amino acids in environmental water), the growth rate for Ezo salamanders was higher when larvae were reared in phenylalanine solution, while that for Japanese black salamanders was higher in glycine and phenylalanine solutions. Amino acids in environmental water had no effect on the growth of Tohoku salamanders. However, when growth was divided into early (days 1 to 5) and late (days 5 to 7) developmental stages, growth in early-developmental stage individuals was improved by phenylalanine treatment, even in Tohoku salamanders. The results showed that the growth of salamander larvae was improved when salamanders were reared in environmental water with high amino acid concentrations. Although aquatic bacteria may not have been removed completely from the environmental water, no other eukaryotes were present. Our results suggest an overlooked nutrient pathway in which aquatic vertebrates take up dissolved amino acids without mediation by other eukaryotes.

Phenotypic Plasticity of Salamander Hatchlings in the Pre-Feeding Stage in Response to Future Prey

Vulnerability of animals immediately after hatching may induce plasticity in early ontology that becomes important for subsequent survival and growth. Ezo salamanders (Hynobius retardatus) are amphibians inhabiting ponds in Hokkaido, Japan where ezo brown frogs (Rana pirica) spawn on occasion. The salamander larvae must achieve sufficient size in order to successfully capture frog tadpoles, and we examined whether the presence of tadpoles causes development of greater body and/or gape size in newly hatched salamander larvae, which will in turn result in advantageous future prey-predator interactions. To examine this hypothesis, we conducted three laboratory experiments to demonstrate the phenotypic plasticity of salamander hatchlings in response to the presence or absence of frog tadpoles and to screen the type of signals involved in the expression of the phenotypic plasticity. First, salamander hatchlings were reared alone or with tadpoles, and the growth and morphological traits of the hatchlings were compared. The results showed that hatchling larvae grew faster with a more developed gape in the presence of tadpoles. Next, to identify the type of signals inducing this plasticity, two separate experiments with manipulated chemical and visual signals from tadpoles were conducted. The findings showed that faster growth and a more developed gape were induced by chemical but not visual signals. This plasticity may be an adaptive strategy because it increases the likelihood of preying on tadpoles in future prey-predator interactions.

Metabolites from Microbes Isolated from the Skin of the Panamanian Rocket Frog Colostethus panamansis (Anura: Dendrobatidae)

The Panamanian rocket frog Colostethus panamansis (family Dendrobatidae) has been affected by chytridiomycosis, a deadly disease caused by the fungus Batrachochytrium dendrobatidis (Bd). While there are still uninfected frogs, we set out to isolate microbes from anatomically distinct regions in an effort to create a cultivable resource within Panama for potential drug/agricultural/ecological applications that perhaps could also be used as part of a strategy to protect frogs from infections. To understand if there are specific anatomies that should be explored in future applications of this resource, we mapped skin-associated bacteria of C. panamansis and their metabolite production potential by mass spectrometry on a 3D model. Our results indicate that five bacterial families (Enterobacteriaceae, Comamonadaceae, Aeromonadaceae, Staphylococcaceae and Pseudomonadaceae) dominate the cultivable microbes from the skin of C. panamansis. The combination of microbial classification and molecular analysis in relation to the anti-Bd inhibitory databases reveals the resource has future potential for amphibian conservation.

Effects of L-proline on swimming parameters of Daphnia magna subjected to heat stress

L-proline (L-PROL) is an essential amino acid, a constituent of many proteins and the osmoprotective molecule produced and accumulated in higher plants and some freshwater microalgae in response to various environmental stressors. Knowledge on thermoprotective effects of this amino acid on freshwater invertebrates is very scarce. Therefore the aim of our study was to determine the effect of L-PROL at concentrations: 10 mg/L, 20 mg/L and 50 mg/L on swimming behavior (immobilization, swimming track density, swimming speed, turning ability) of Daphnia magna subjected to temperatures: 22 °C, 35 °C and 38 °C. We found that L-PROL elevated all the measured swimming parameters at 22 °C when compared to the untreated crustaceans. Furthermore, L-PROL alleviated heat-induced inhibition of these parameters in the experimental animals subjected to 35 °C. The results suggest that L-PROL stimulates swimming performance and alleviates alterations of swimming parameters induced by heat stress in D. magna. Moreover, these findings may support the hypothesis that in natural conditions, L-PROL may protect crustaceans against thermal stress.