ALBERT

Description: Metabolic regulation, control of gene expression or the evolutionary origin of new proteins are examples of biochemical adaptations that allow organisms to survive within a wide spectrum of environmental conditions. The North Sea shrimp Crangon crangon has high reproduction rates. It is an opportunistic feeder and shows to be well adapted to heterogeneous and variable environmental conditions. Previous studies revealed unusual expression patterns and isoforms of digestive enzymes with a high variability between individuals and between seasons. Such a pronounced variability is not common in other decapod species. The unspecific feeding habits of C. crangon can be seen as an adaptation to a variable environment. This may be supported by the heterogeneity of digestive endopeptidases due to the variability of food sources. Previous studies showed protein polymorphism as a phase in molecular evolution. It represents the first step in the long‐lasting establishment of mutations within populations. The reasons for the unusual heterogeneity of digestive enzymes in C. crangon are not yet clear, but a better understanding of this phenomenon can help to explain the extraordinary performance of C. crangon in a highly variable environment. We obtained the transcriptome of midgut gland tissue from C. crangon, which we used as a basis for gene expression analyses. Additionally, the obtained sequences were analysed for isoforms of the key digestive enzymes. First results indicate that the expression of digestive enzymes in C. crangon follow a similar pattern as previously seen in enzyme activities. Cysteine proteinases seem to have more isoforms participating in the extracellular digestion than serine proteinases. This approach will help to better understand processes that modulate the unique expression pattern of digestive enzymes and biochemical strategies that allow this species to exist in a very variable environment.

Description: Environmental fluctuations can impose energetic constraints on organisms in terms of food shortage or compensation for metabolic stress. To better understand the biochemical strategies that support adaptive physiological processes in variable environments, we studied the lipid dynamics of the brown shrimp Crangon crangon and the pink shrimp Pandalus montagui by analysing their midgut glands during an annual cycle. Both species have an overlapping distribu- tion range in the southern North Sea, but differ in their habitat preferences, reproductive strate- gies, and life-history traits. C. crangon showed minor total lipid accumulation in their midgut glands, ranging between 14 and 17% of dry mass (DM), dominated by phospholipids. In contrast, P. montagui stored significantly larger amounts of total lipid (47−70% DM, mainly triacylglycer- ols) and showed a distinct seasonal cycle in lipid accumulation with a maximum in summer. Fatty acid trophic markers indicated a wide food spectrum for both species, with higher preferences of P. montagui for microalgae. In C. crangon, feeding preferences were less distinct due the low total lipid levels in the midgut gland. PCA based on fatty acid compositions of both species suggested that C. crangon has a broader dietary spectrum than P. montagui. C. crangon seems to have the capacity to use sufficient energy directly from ingested food to fuel all metabolic requirements, including multiple spawnings, without building up large lipid reserves in the midgut gland. P. montagui, in contrast, relies more on the energy storage function of the midgut gland to over- come food scarcity and to allocate lipids for reproduction.

Description: The brown shrimp, Crangon crangon, is well adapted to the variable environmental conditions in the southern North Sea. It is very abundant, has high reproduction rates, and holds a key position in coastal ecosystems. This species has very low lipid deposits in the midgut gland, suggesting that the main function of the midgut gland is metabolic turnover rather than energy storage. Based on seasonal gene expression studies and established transcriptome data, we investigated key components of lipid metabolic pathways. Gene expression of triacylglycerol lipase, phospholipase, and fatty acid desaturase were analyzed and compared with that of other digestive enzymes involved in lipid, carbohydrate, and protein catabolism. Our results suggest that gene expression of digestive enzymes involved in lipid metabolism is modulated by the lipid content in the midgut gland and is related to food availability. Brown shrimp seem to be capable of using cellular phospholipids during periods of food paucity but high energetic (lipid) requirements. Two of three isoforms of fatty acid binding proteins (FABPs) from the midgut gland involved in fatty acid transport showed specific mutations of the binding site. We hypothesize that the mutations in FABPs and deficiencies in anabolic pathways limit lipid storage capacities in the midgut gland of C. crangon. In turn, food utilization, including lipid catabolism, has to be efficient to fulfill the energetic requirements of brown shrimp.

Description: The brown shrimp Crangon crangon shows high reproduction rates, feeds opportunistically on endo- and epibenthic organisms and is apparently well adapted to variable environmental conditions. Previous electrophoretic studies revealed a high level of polymorphism and no consistent phenotype of digestive enzymes between individuals. In order to understand the biological reason of digestive enzymes polymorphism and underlying biochemical processes, we performed a transcriptome-based study of digestive enzymes of C. crangon. Detailed sequence analyses of triacylglycerol lipase, phospholipase A2, alpha-amylase, chitinase, trypsin and cathepsin L were performed to identify putative isoforms. The number of isoforms varied among enzymes: for lipases, phospholipase A2 showed a higher number of isoforms than triacylglycerol lipase, while carbohydrase chitinase showed a higher number of isoforms in comparison with alpha amylase. Furthermore, cysteine proteinases showed a lower polymorphism than serine proteinases. We propose that the expression of polymorphic digestive enzymes indicates high plasticity in food utilization by the brown shrimp. Alternative splicing may be the driving force of the heterogeneous patterns of digestive enzymes in C. crangon.

Description: Tolerance of organisms towards heterogeneous and variable environments is highly related to physiological flexibility. An effective strategy to enhance physiological flexibility is the expression of polymorphic enzymes. This seems to be the case in the brown shrimp Crangon crangon. It shows high reproduction rates, feeds opportunistically on endo- and epibenthic organisms, and is apparently well adapted to variable environmental conditions. Previous electrophoretic studies revealed a high level of polymorphism and no consistent phenotype of digestive enzymes between individuals. In order to understand the underlying biochemical processes, we carried out a transcriptome-based study of digestive enzymes of C. crangon. Detailed sequence analyses of triacylglycerol lipase, phospholipase A2, alpha amylase, chitinase, trypsin and cathepsin L were performed to identify putative isoforms. The number of isoforms, and thus the degree of polymorphism varied among enzymes: lipases and carbohydrases showed higher numbers of isoforms in enzymes that besides their extracellular function also have diverse intracellular functions. Furthermore, cysteine proteinases showed a lower polymorphism than serine proteinases. We suggest that the expression of enzyme isoforms improves the efficiency of C. crangon in gaining energy from different food sources.