Spotted seals (Phoca largha) are small-bodied pinnipeds that are generally distributed in the cold sea area of the North Pacific Ocean. P. largha has been listed as one of the most endangered species in China and South Korea due to the destruction of their habitat by anthropogenic impacts. For many wild animals, captivity in artificially-controlled environments is one of the most effective ways to ensure their conservation. During the past decades, China has continuously implemented artificial breeding and rearing activities for the maintenance of the P. largha population. At present, more than 1000 spotted seals are in captivity in the aquarium of China, accounting for 50% of the total population. Despite advances in species conservation, captivity has also been shown to affect genetic and physiological characteristics in a variety of animals. For example, significant differences in genetics and morphology were observed between wild and captive Leon Springs pupfish, Cyprinodon bovines. In addition, wild Indian leopards, Panthera pardus fascia, showed higher nucleotide diversity and amino acid polymorphisms in major histocompatibility complex genes and proteins compared to captive individuals. Moreover, differences in the concentration of plasma cortisol between captive and wild harbor seals (P. vitulina) of the same sex and during the same season were highly significant. Nonetheless, no research has been performed to describe the potential physiological differences between wild and captive spotted seals.

Previous investigations in spotted seals mainly focused on their distribution , development8, and genetic diversity. To date, only a few studies explored the physiological characteristics of spotted seals at the molecular level. Gao et al.1 assembled the transcriptome in liver and spleen of spotted seals and identified 193 unigenes associated with defense mechanisms. In addition, the normal levels of hematology and serum biochemistry indices in the captive spotted seals were measured, and the age- and gender-related differences in those indices were obtained. Moreover, the relationships between sexual maturation and the concentrations of serum testosterone, progesterone, and estradiol in captive spotted seals were also reported. The physiological functions of all organisms are achieved through the “gene-mRNA-protein” pathway. Studies at the gene and mRNA levels do not completely reflect the physiological functions of organisms due to pre- and post-transcriptional regulation. Proteins are the direct performers of biological functions, and thus, measuring protein expression profiles is a powerful way to understand the physiological characteristics of spotted seals.

Proteomics technologies evaluate the complete protein composition expressed by a genome, cell or tissue, and provide powerful tools to examine the physiological functions of animals. Over the years, qualitative proteomics techniques based on mass spectrometry (MS), such as 2D-gel-MS, have developed into the most direct and accurate methods for identifying the proteins in animal samples. However, such traditional techniques have many shortcomings, including their inability to quantitatively recognize the differentially expressed proteins (DEPs) and their poor detection of low-abundance proteins. Hence, a quantitative proteomics technology, named label-free shotgun proteomics, was developed to determine DEPs with extreme accuracy, sensitivity, discrimination, and high-throughput. At present, label-free shotgun proteomics has been widely used in humans, plants, and microorganisms. Therefore, comparative proteomics research based on label-free shotgun proteomics is suitable for a more comprehensive comparison of the physiological functions between wild and captive spotted seals.

In the present study, preliminary whole blood protein expression profiles for wild and captive P. largha pups were determined using the label-free shotgun proteomics technology. The objectives of this study were to (1) describe the preliminary whole blood protein composition patterns of P. largha pups; (2) provide an overview of the differences in the whole blood proteomes between wild and captive P. largha pups; and (3) identify the key proteins that may potentially alter the physiological functions of P. largha pups due to captivity.

Regards,

Jessica

Managing editor

International journal of pure and applied zoology