International Journal of Aquaculture, 2025, Vol.15, No.5, 255-265 http://www.aquapublisher.com/index.php/ija 262 In addition to morphological adaptation, the behavioral and reproductive isolation mechanisms of cichlids also promote rapid species formation. Many cichlids are oral hatched fish, and females hatch fertilized eggs in their mouths. During courtship, the female fish will select the body color and pattern of the specific male fish for mating. Svardal et al. (2019) genome research found that the gene communication of Lake Malawi cichlids is complex, and multiple lineage radiation is connected to each other through hybridization networks, rather than simply tree-like bifurcations (Figure 2). This means that during the radiation process, different new species do not evolve completely independently, but occasionally infiltration, which accelerates the spread of adaptive genes among populations and promotes diversity. Figure 2 Sampling and genetic relationships. (a) Map of East African river catchments and sampling locations. (b) NJ tree of pairwise genetic distances between all samples (Adopted from Svardal et al., 2019) 7 Integration of Fossil Record and Molecular Evidence 7.1 The role of fossil calibration in molecular clock estimation The molecular clock method can calculate the time when species divergence occurs by comparing the differences in DNA or protein sequences in different species, combined with a relatively constant rate assumption. However, the molecular clock must be calibrated to obtain absolute time, which requires the help of fossil recording. The origin time of many major taxa is directly anchored by key fossils (Nguyen and Ho, 2020). The differences between radial-finned fish and meat-finned fish can be calibrated by the earliest bone fish fossils at the end of the Silurian (about 420 million years ago); the differences between shark-shaped and ray-shaped can be referred to as the appearance time of the teeth fossils of cartilage fish in the early Devonian period; the differentiation of the large branches of true bone fish can be based on the presumption of the primitive bone tongue fish and the whole bone fish fossils from the Late Triassic-early Jurassic. Wu et al. (2019) used the molecular biogeographic study of climbing perch (a freshwater fish), and calibrated the origin time of the family Climbing perch. Combined with other fossil constraints, their molecular clock analysis infers that the Climbing Peridae diffuses into Africa through the Indian plate during the Eocene. 7.2 Application of interdisciplinary methods in evolutionary path analysis Research on fish evolution paths is showing a trend of highly interdisciplinary integration. In addition to paleontology and molecular biology, the integration of the following disciplines and methods is promoting new developments in fish evolution research: Geological and paleogeographic analysis links the location of fish fossil discovery with plate movements and paleoenvironmental changes in geological history, which can explain the geographical background of biological evolution. By constructing paleogeographic models, researchers found that the Tarim plate was adjacent to the South China plate during the Silurian period, providing the possibility for the cross-regional distribution of
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