Genetic legacy of tertiary climatic change: a case study of two freshwater loaches, Schistura fasciolata and Pseudogastromyzon myersi, in Hong Kong

Abstract

The high biodiversity and strong population structure of freshwater fauna has often been attributed to historical geological and climatic alterations. The impact of these historical changes on obligate freshwater species on a small geographical scale has not been well understood due to the lack of fine-scale comparative phylogeographic studies. Strong population structure has been reported in a goby and a caridean shrimp in Hong Kong, a small but highly developed city in South China, but the common drivers of population differentiation in freshwater fauna in this region remain unclear. This study examined the fine-scale phylogeographic patterns of two freshwater loaches, Schistura fasciolata and Pseudogastromyzon myersi in Hong Kong, using sequence data of mitochondrial control region and two nuclear markers (interphotoreceptor retinoid binding protein gene 2 and ribosomal protein S13 gene). Results show that they exhibit pronounced population structure as supported by high and significant Φ. Phylogenetic analyses based on the control region reveal six and three distinct lineages in S. fasciolata and P. myersi, respectively. Phylogeographic structure of both species generally follows the paleodrainage pattern, though P. myersi shows a shallower structure on the Mainland, perhaps due to their higher mobility. Most of these lineages diverged during the Pliocene and Late Pleistocene, a period with marked sea-level fluctuations. In a broader context, this suggests that sea-level fluctuation played an important role in shaping even the fine-scale population structure of freshwater fish in South China, implying that the genetic diversity of this fauna may be higher than expected.

The Sea-Level Changes in Hong Kong From Tide-Gauge Records and Remote Sensing Observations Over the Last Seven Decades

“…This value is much higher than the global mean sea level rate of 3.3 mm/yr during past 27 years (Figure 15) [64,65]. The reason may be due to anomalous atmospheric and sea surface temperature [41,54,58,66]. Comparison the regional sea level changes in Hong Kong with the sea level changes in the South China Sea and global mean sea level indicates that regional sea level fluctuations in Hong Kong agreed well with sea level changes in the South China Sea (Figure 15).…”

“…Both TBT and SPW stations are located at the Pearl River Estuary. This finding is explained by the freshwater discharge and sedimentation at the estuary that are responsible for larger periodic fluctuations in sea level trend at the western side of Hong Kong [24,54]. On the other hand, the amplitudes of main tidal components at the four stations at the eastern coast of Hong Kong are relatively consistent.…”

Genetic Structure of an East Asian Minnow (Toxabramis houdemeri) in Southern China, with Implications for Conservation

“…For effectively managed conservation, it is critical to understand the spatial configurations of genetic diversity and to excavate genetic endemism (unique genetic resources in a particular geographic region) within species, particularly in the case of widespread species. In particular, since widely distributed populations of freshwater fish may frequently be isolated by mountains or salinity [ 1 ], gene flow is likely to be interrupted, and genetic differentiation and/or endemism may occur within populations [ 2 , 3 , 4 , 5 , 6 , 7 ]. In addition, it has been argued that river rearrangements triggered by glacial cycles may have both blocked gene exchange by isolating previously connected rivers and promoted population dispersal by connecting previously isolated rivers [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ].…”

“…In particular, since widely distributed populations of freshwater fish may frequently be isolated by mountains or salinity [ 1 ], gene flow is likely to be interrupted, and genetic differentiation and/or endemism may occur within populations [ 2 , 3 , 4 , 5 , 6 , 7 ]. In addition, it has been argued that river rearrangements triggered by glacial cycles may have both blocked gene exchange by isolating previously connected rivers and promoted population dispersal by connecting previously isolated rivers [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. River rearrangements have historically been more common in rivers near the sea [ 4 , 7 ].…”

“…Several genetic studies of freshwater fish in southern China have detected high levels of population differentiation [ 2 , 3 , 7 , 8 , 9 , 10 , 13 ]. For example, Yang and He [ 2 ] found that river landscape changes induced by the Pleistocene glacial cycles were significant drivers of the high levels of population divergence within Hemibagrus guttatus populations in the Pearl River, Hanjiang River, and Jiulongjiang River [ 2 ].…”