International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.4, 153-162 http://ecoevopublisher.com/index.php/ijmec 15 7 3.3 Genetic bottlenecks and founding effects of invasive populations When black fish are introduced to new habitats, a population is usually established by only a small number of individuals, and thus may experience a decline in genetic diversity, namely the "founding effect" and genetic bottleneck. This is a common phenomenon in many invasive species: due to the limited number of initial invasive individuals, genetic variation is lower than that in the original habitat, which theoretically may limit their potential for adaptive evolution (Bock et al., 2016). However, the situation of the northern black fish in the United States indicates that multiple independent introductions and cross-mating may have alleviated the genetic bottleneck to a certain extent. Microsatellite analysis of several invasive populations in the eastern United States by Wegleitner et al. (2016) indicated that the genetic structures of northern blackfish in different rivers were different from each other, and it was inferred that at least two or more independent introduction events occurred. The introduction of multiple sources has led to a relatively high degree of genetic variation, and even cases of "genetic hybridization" due to interbreeding of different source lineages have occurred. Both theory and experience indicate that higher genetic diversity is conducive to the successful adaptation of invasive populations to new environments (Cristescu, 2016). Therefore, the genetic bottleneck effect of the black fish invasion population may be offset by multiple introductions. Conversely, if invasive populations reproduce in isolation for a long time and lack the inflow of new genes, there may be signs of reduced genetic diversity. For example, some interstate isolated pond populations have lower genetic variations and are presumed to be the offspring of a single event (Wegleitner et al., 2016). 4 The Ecological and Genetic Mechanisms of the Invasive Spread of Black Fish 4.1 The promoting effect of biological characteristics on diffusion The biological characteristics of the black fish species themselves are the basis for them to become successful invaders. These fish possess a series of adaptive characteristics that are conducive to diffusion and colonization. In terms of respiration, black fish have both gill respiration and assisted air respiration capabilities. They can survive in water bodies with low dissolved oxygen and crawl out of the water briefly when necessary to search for new ponds or rivers (Resh et al., 2021). In terms of reproduction, a high reproduction rate and parental child-rearing behavior significantly increased the growth rate and stability of invasive populations (Odenkirk and Isel, 2016). In terms of nutritional ecology, black fish, as one of the top predators, possess extremely strong adaptability to food and high hunting efficiency. They feed on a wide variety of species, ranging from fish and shrimp to amphibians, reptiles, and even small mammals (Li et al., 2016). The migration behavior of black fish is also worthy of attention. Although most of the time they inhabit still water environments such as lakes and ponds, they will move long distances along streams or ditches when resources are scarce or their habitats change (Love and Newhard, 2012). 4.2 Human activities and cross-border communication paths The global invasion of black fish largely depends on long-distance transmission routes mediated by humans. Under natural conditions, even if black fish have a certain ability to migrate over land, their spread is mainly confined within connected water systems or short adjacent waters. However, human means of transportation and trade networks have provided "transportation corridors" for black fish to cross continents and oceans (Harrington et al., 2022). Take the northern black fish as an example. Its introduction from East Asia to North America clearly could not be achieved through natural distribution, but was carried there by humans through aircraft, ships, etc. The ornamental fish industry has also formed a global network. Many black fish species are classified as tropical fish and are exported to the aquarium markets in Europe, America, Japan and other places by air. The risk of this path lies in the fact that once ornamental fish enthusiasts or merchants release black fish into the wild, it may trigger colonization. From this, it can be seen that the global spread of black fish is not simply a "spontaneous drift", but more like taking the "express train" of human logistics (Evers et al., 2019; Maia et al., 2025).
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