Invasive alien species are one of the three major threats to biodiversity. The report of the 20th National Congress emphasized the necessity of "strengthening biosecurity management and preventing the invasion of exotic species". Trachemys scripta elegans, which is native to the eastern United States and northeastern Mexico, has been invaded worldwide except for Antarctica due to its rapid growth and development, high fertility, and omnivorous, and it has been listed by the IUCN as one of the 100 most harmful invasive alien species in the world. Although T. s. elegans is found in many wild environments in our country, the public's attention on its danger has mainly remained articles in newspapers and reports on the internet. Therefore, we carried out a series of studies:

1. Revealed the invasion status and ecological adaptation mechanism of T. s. elegans in China

T. s. elegans can reproduce in the wild in China, with strong competitive advantage and dispersal ability. This species can reproduce in natural habitats such as Guangdong and Hainan, and has reached the invasion stage of self-propagation. The population shares of T. s. elegans in Jiangsu and Hainan reached 60.2% and 85.7%, respectively, which have significantly exceeded the sum of native chelonians species.

This species is distributed in all provinces in China, and it lives in the same environment as more than two-thirds of the native chelonians. However, it has a wide ecological niche, strong adaptability to invasive habitats, and a competitive advantage in spatial resources.

T. s. elegans is omnivorous and the foods ingested by them belong to 14 orders and 18 families, with animal diets including shellfish, shrimps, crabs, fishes, frogs, lizards, birds and rodents, and plant diets including stems, leaves, flowers and seeds of plants from nine families.

Therefore, the invasion of this species will threaten the survival of native species, change the structure of the food web, and affect the biodiversity and stability of the native ecosystem.

2. Revealed the physiological mechanism of T. s. elegans adapting to the brackish water environment.

 Although T. s. elegans is a freshwater turtle, field surveys found that it is distributed and can lay eggs and reproduce in the brackish watershed of the Nandujiang River in Hainan (Salinity: 5.3-14.6‰), which suggests that it can invade the brackish water. As most of the brackish water are located in the red line of ecological protection, previous predictions and studies on the invasion area of T. s. elegans have neglected this vast area of extremely rich biodiversity and the potential invasion range of T. s. elegans. In the process of global warming, the accelerated rise in sea level causes saltwater intrusion, which in turn leads to increased freshwater salinization. Therefore, the invasion area of T. s. elegans may expand significantly in the future, greatly expanding the hazardous and defensive range of the species.

A series of studies found that T. s. elegans maintains osmotic pressure balance inside and outside the organism by increasing the content of ions and organic osmolytes in plasma, activates the AMPK signalling pathway to regulate glucose and lipid metabolism, and provides the energy required by the organism to cope with the osmotic pressure regulation; and enhances antioxidant defence and immunomodulation to maintain survival by adjusting the function of intestinal barriers and activating the signaling pathways such as Nrf2-TOR, NF-κB and JAK-STAT.

These adaptive mechanisms can be used to predict the invasive potential of T. s. elegans. We also suggest that future research should focus on the behaviour, physiological regulation of freshwater turtles in brackish water and the impact of invasive species on other chelonians living in brackish water.