International Journal of Marine Science, 2025, Vol.15, No.1, 35-44 http://www.aquapublisher.com/index.php/ijms 40 6 Genomic Characteristics of Environmental Adaptation 6.1 Adaptation to deep-sea chemoenvironment Decapod shrimps have a wide distribution range, from the darkness of the deep sea to the cold waters of high latitudes, from tropical shallows to freshwater rivers. Such an ecological span naturally forces them to develop a set of unique adaptation strategies in their long evolution. Especially in the extreme environment of deep-sea hydrothermal vents, such as some species of Alvinocarididae, the darkness, high temperature, and high sulfide concentration are almost forbidden areas for life. But these shrimps are alive and well, relying on a special symbiotic system that has evolved - a large number of chemoenergetic bacteria parasitize on the gills and obtain energy through bacterial metabolism. The comparison results of the genome and transcriptome also confirm this: this type of deep-sea shrimp has lost a lot of vision-related genes (after all, eyes are not used in a completely dark environment), and genes related to sulfide detoxification and metabolism have expanded or positively selected (Yuan et al., 2020). Other studies have found that their hemocyanin genes have also undergone adaptive changes, improving their oxygen-carrying capacity in low-oxygen environments (Choi et al., 2025). These changes in the genome support the ability of deep-sea shrimp to survive and reproduce in extreme environments at multiple levels. 6.2 Salinity and water conversion adaptation Of course, the adaptation story of shrimp is not just as simple as the deep sea. It is also common for shrimp to independently invade freshwater from seawater many times, or simply take root in intertidal zones and brackish water areas. Unlike the seawater environment where their ancestors lived, the low ionic strength in freshwater places higher demands on osmotic regulation ability. Through comparative genomic studies, scientists have found that some freshwater shrimps (such as freshwater crayfish and freshwater prawns) have expanded many gene families related to osmotic pressure regulation, such as Na+/K+-ATPase and calmodulin, which are significantly richer than marine species (Liu et al., 2020). In addition, the endocrine system that controls molting and shelling has also been quietly adjusted in freshwater populations to cope with changes in the water chemical environment. For example, when Wang et al. (2022) compared the genomes of Chinese shrimp and Penaeus vannamei, they found that Chinese shrimp had unique copy number changes or amino acid substitutions in genes related to low-salinity stress. These "little moves" in genes may be the secret to their ability to adapt to the low-salinity environment near the Yellow Sea. As for the shrimps that stay in the intertidal zone, such as the shrimps living in the mangroves, they also expand their antioxidant and anti-interferon protein genes in order to cope with the pressure of alternating dry and wet conditions and freshwater flushing. In general, different salinity environments pose different survival challenges to shrimps, and the changes in the shrimp genome are the key behind their success. 6.3 Adaptation to terrestrial and semi-terrestrial environments There are a few shrimp relatives in the Decapoda (strictly speaking, they belong to the suborder Anomura, such as crabs) who have evolved terrestrial habits after landing, but most typical shrimps are still aquatic. However, some cases are worth learning from, such as the coconut crab (Birgus latro), which is a completely terrestrial species evolved from hermit crabs. Although it is not a shrimp, it is closely related to shrimp, and its genome comparative study provides a useful reference. Veldsman et al. (2021) compared the genomes of coconut crabs with those of closely related aquatic crabs and shrimps and found that the coconut crab genome had a significant expansion of genes in functional categories such as amino acid metabolism and nitrogen waste treatment. It is speculated that this is the result of adapting to the high-ammonia environment on land and a lifestyle such as feeding on plants. At the same time, the coconut crab genome shows a unique pattern of alternative splicing, and many genes produce different transcripts through splicing, which helps to flexibly regulate physiology in dry and wet season environments. These findings suggest that if real landed shrimps are found in the future (such as some intertidal crayfish that stay out of water for a long time), their genomes may also show similar adaptive changes, such as functional enhancement of genes such as respiratory proteins and epidermal proteins. Although decapod shrimps are currently mainly confined to aquatic environments, the experience of genomic research on semi-terrestrial adaptation is inspiring for understanding environmental transformation.
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