International Journal of Marine Science, 2025, Vol.15, No.2, 92-106 http://www.aquapublisher.com/index.php/ijms 95 prawnaceae species may have originated from Guttisyang, undergoing radiation evolution in the IWP region formed by plate drift. Historical biogeographic analysis by Frolová et al. (2022) suggests that the current diversity of basal shrimps such as the Long-armed Shrimp family originates to a large extent from the IWP region, and it is speculated that the main lineages have been nurtured in the Late Cretaceous (about 91 million years ago) and then spread outward (Frolová et al., 2022). Why IWP has become the center of shrimp origin and differentiation? On the one hand, the region has been connected for a long time in geological history. The Paleo-Mediterranean (Tetis Sea) period provided a stable and vast habitat for Indo-Pacific waters, which is conducive to the continuous evolution of species (Saulsbury and Baumiller, 2022). On the other hand, the IWP region has a warm climate, high productivity and diverse habitat types, which promotes high radiation adaptation of species. In addition, before the Late Miocene, the sea access from East Africa to the Western Pacific basically maintained unobstructed, allowing species to spread widely within the Indo-Pacific. This is also confirmed by the modern distribution pattern: many prawn and basal shrimp species have the greatest diversity in the Indo-Pacific Ocean, while relatively few species are found in the corresponding latitude areas of the Atlantic Ocean or the Eastern Pacific. 3.2 Comparison of regional characteristics between the Eastern Pacific and the Western Atlantic Ocean The Eastern Pacific and Western Atlantic Oceans are two geographically isolated marine areas, and there are obvious differences in their shrimp regions and population characteristics. In terms of species composition, large marine shrimp species in the Eastern Pacific (especially the eastern coast of the American Pacific) are relatively poor, and are known as the "East Pacific Species Poverty Zone". Along the tropical coast of the Eastern Pacific, large shrimps with commercial value are mainly Pacific white shrimp (native to the eastern Pacific coast) and a few close species, In contrast, the corresponding latitudes of the western Atlantic (along the American Atlantic coast) are home to a variety of penaeid shrimp species, including the white shrimp (Penaeus setiferus), brown shrimp (Penaeus aztecus), and northern white shrimp (Penaeus schmitti). The formation of this difference is closely related to geological historical events (Valles-Jiménez et al., 2006). From the perspective of genetic diversity, western Atlantic shrimp populations tend to have higher genetic variations, while eastern Pacific side populations have shown signs of bottleneck in some studies. Take the Pacific white shrimp as an example. The native Eastern Pacific population has experienced fluctuations in population size in history, and its mitochondrial genetic diversity is lower than that established later in Asia. In terms of geographical distribution range, the distribution of many shrimp species in the Eastern Pacific is relatively narrow in the north and south, which is related to the narrow continental shelf and unique cold currents along the Eastern Pacific coast; while the continental shelf along the Western Atlantic coast is wide, providing a broader adaptable environment for shrimps (Farias et al., 2023). 3.3 The restrictive effect of marine geographical disorders on gene flow Geographic barriers in the ocean play a significant restrictive role in genetic communication of shrimp populations. Famous marine barriers include vast ocean barrier-free areas, cold waters, ocean current boundaries, and land barriers. These factors can prevent shrimp larvae or adults from spreading freely between different regions, thereby contributing to population differentiation. The East Pacific Barrier refers to an open deep-sea area that lasts thousands of kilometers from the coast of Central America to the South Pacific Islands, and is an insurmountable barrier for nearshore creatures. This barrier has been around since the Cenozoic, preventing many Indo-Western Pacific species from naturally crossing the Eastern Pacific to reach the coast of the Americas, resulting in a relatively poor biological poverty in the eastern Pacific nearshores, known as one of the largest biogeographic barriers in the global ocean. For example, the Panama Isthmus finally closed about 3 million years ago, forming a solid land barrier that completely separates marine life from the Atlantic Ocean and the Pacific Ocean. This "hard barrier" directly terminates gene exchange between the two oceans, causing the once connected populations to evolve independently, and is considered to be the main reason for the formation of many shrimp "sister species" (McCartney et al., 2000). In addition, the Guttis Seaway between the Indian Ocean and the Atlantic gradually disappeared during the Miocene, resulting in biological isolation between the Indian Ocean and the Eastern Atlantic Ocean. There are also some "soft obstacles", such as cold water masses and ocean currents: for example, cold water at the southern end of Africa makes it difficult for shrimps in the Indian Ocean to bypass
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