Abstract
BackgroundThe Antarctic krill Euphausia superba is a keystone species in the Antarctic food chain. Not only is it a significant grazer of phytoplankton, but it is also a major food item for charismatic megafauna such as whales and seals and an important Southern Ocean fisheries crop. Ecological data suggest that this species is being affected by climate change and this will have considerable consequences for the balance of the Southern Ocean ecosystem. Hence, understanding how this organism functions is a priority area and will provide fundamental data for life history studies, energy budget calculations and food web models.Methodology/Principal FindingsThe assembly of the 454 transcriptome of E. superba resulted in 22,177 contigs with an average size of 492bp (ranging between 137 and 8515bp). In depth analysis of the data revealed an extensive catalogue of the cellular chaperone systems and the major antioxidant proteins. Full length sequences were characterised for the chaperones HSP70, HSP90 and the super-oxide dismutase antioxidants, with the discovery of potentially novel duplications of these genes. The sequence data contained 41,470 microsatellites and 17,776 Single Nucleotide Polymorphisms (SNPs/INDELS), providing a resource for population and also gene function studies.ConclusionsThis paper details the first 454 generated data for a pelagic Antarctic species or any pelagic crustacean globally. The classical “stress proteins”, such as HSP70, HSP90, ferritin and GST were all highly expressed. These genes were shown to be over expressed in the transcriptomes of Antarctic notothenioid fish and hypothesized as adaptations to living in the cold, with the associated problems of decreased protein folding efficiency and increased vulnerability to damage by reactive oxygen species. Hence, these data will provide a major resource for future physiological work on krill, but in particular a suite of “stress” genes for studies understanding marine ectotherms' capacities to cope with environmental change.
Highlights
The Southern Ocean is an important breeding and/or foraging location for a wide range of charismatic megafauna such as whales, seals, penguins and other sea birds including albatrosses
The classical ‘‘stress proteins’’, such as HSP70, HSP90, ferritin and Glutathione S-transferase (GSTs) were all highly expressed. These genes were shown to be over expressed in the transcriptomes of Antarctic notothenioid fish and hypothesized as adaptations to living in the cold, with the associated problems of decreased protein folding efficiency and increased vulnerability to damage by reactive oxygen species
Because the aim of this project was to conduct a preliminary characterisation of the krill transcriptome, with, as described below, an emphasis on chaperones and stress-related genes for future analyses there was a requirement for longer sequences of good quality which would enable us to distinguish between gene family members
Summary
The Southern Ocean is an important breeding and/or foraging location for a wide range of charismatic megafauna such as whales, seals, penguins and other sea birds including albatrosses. Whilst these species fascinate the public, they represent the apex of a complex food chain, the keystone species of which is the Antarctic krill Euphausia superba [1]. The Antarctic krill Euphausia superba is a keystone species in the Antarctic food chain Is it a significant grazer of phytoplankton, but it is a major food item for charismatic megafauna such as whales and seals and an important Southern Ocean fisheries crop. Understanding how this organism functions is a priority area and will provide fundamental data for life history studies, energy budget calculations and food web models
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