Human disturbance as a possible cause of genetic introgression from exotic into native Mauremys turtles

The Kinmen Islands on the coastline of China represent a recent case of the protection of endangered wildlife in a demilitarized zone. These islands represent the last remaining habitat in southeastern China that supports a healthy natural population of Reeves’ turtle Mauremys reevesii. However, human-mediated dispersal appears to have aided the establishment of an introduced population of the Chinese stripe-necked turtle M. sinensis since the late 1990s, resulting in population mixture of the two congeners. To evaluate the potential impacts of hybridization, we evaluated the magnitude of genetic introgression in ponds on Kinmen using mitochondrial cytochrome b sequences and 13 microsatellite loci. We further used eight environmental and biological factors of the ponds to conduct general linear regression model analysis between environmental factors and the magnitude of genetic introgression. Among the 41 sampled ponds, M. reevesii was recorded in 21, of which 12 ponds (57.1%) contained genetic hybrids or backcrosses, corresponding to 11.3–12.7% of the total individuals on the islands. The magnitude of genetic introgression was positively correlated with the amount of introduced M. sinensis occurring in a pond, and marginally negatively associated with the shortest distance from the pond to secondary roads. We conclude that this considerable genetic introgression is attributable to human-mediated dispersal of M. sinensis; roads and habitat modification may increase the likelihood of unexpected encounters between these two congeners.