Hidden invasiveness of non-native Schlegel's Japanese gecko (Reptilia: Squamata: Gekkonidae) and three-way competition among natives and non-natives in Japan.

In this study, we investigated the invasiveness of Gekko japonicus, a prevalent gecko species in Japan and an ancient non-native species, focusing on its competition with both the undescribed endemic Gekko species (referred to as Nishiyamori in Japanese) and G. hokouensis. These species are co-distributed with G. japonicus, leading us to hypothesize that G. japonicus was invasive upon its initial introduction. We employed niche analysis and population genetics through ddRAD-seq to assess the historical invasiveness of G. japonicus by comparing regions with and without interspecies competition. Our niche analysis across the Goto Islands, Hiradojima Island (colonized by G. japonicus) and the Koshikishima Islands (not colonized by G. japonicus) indicated that endemic Gekko sp. alter their microhabitat usage in response to invasions by other gecko species, despite having similar suitable habitats and microhabitat preferences. Population genetic analysis revealed significant population declines in Gekko sp. within areas of introduced competition, in contrast to stable populations in areas without such competition. These findings suggest a tripartite competitive relationship among the gecko species, with G. japonicus and G. hokouensis invasions restricting the distribution of the endemic Gekko sp. Consequently, G. japonicus may have historically acted as an invasive species. Acknowledging the historical dynamics of current biodiversity is crucial for addressing complex ecological issues and making informed conservation decisions.

The mutual history of Schlegel's Japanese gecko (Reptilia: Squamata: Gekkonidae) and humans inscribed in genes and ancient literature.

Knowing how the present distribution of organisms was formed is an essential issue in evolutionary ecology. Recently, the distribution of organisms on Earth has been significantly changed by human-mediated dispersal due to globalization. Therefore, significant attention has been paid to such processes. However, although humankind has taken considerable time to achieve modernization, the impact of ancient human activity on ecosystems has not yet been thoroughly studied. We hypothesized that ancient urban development and transitions had a non-negligible effect on species distribution. Inferring the impact of past human activity on ecosystems from ancient literature and verifying that impact by genetic analysis and human history is an effective means of tackling this problem. As geckos, a popular neighbor of human dwellings, are good material for this model, we performed this combination approach using Schlegel's Japanese gecko, Gekko japonicus. We show that G. japonicus migrated from China to the western Japanese archipelago before Christ. The gecko species dispersed itself from western to eastern the archipelago on a time scale of thousands of years. There are many synchronizations between the dispersal history of G. japonicus and the historical development of human society. It is suggested by such synchronizations that humans have influenced the distribution of G. japonicus many times throughout its dispersal history.

Secondary contact of two cryptic Hokou gecko groups in the Izu Islands, Japan.

We analyzed the mitochondrial DNA of Gekko hokouensis collected from the Izu Islands (maybe an introduced population) and the Nansei Islands (native population), both in Japan. A molecular phylogenetic analysis suggested that G. hokouensis of Japan belongs to a cryptic monophyletic group different from that of the currently discovered sample of China. Furthermore, the Japanese clade of G. hokouensis is differentiated into two subclades (Clade 1 and Clade 2 in this article). In the Nansei Islands, these two subclades form a complicated nested-distribution pattern and do not coexist on any of the islands, whereas both clades appear to coexist in the Izu Islands. The two clades exhibit high genetic diversity in the Nansei islands, which are the source population. Surprisingly, it has been revealed that high genetic diversity has also been maintained in the Izu Islands, which are the introduced population, in each clade. AMOVA has also revealed that the genetic differentiation between the populations in the Izu Islands and the Nansei Islands was not significant in each clade. These results suggest that the population of the Izu Islands is now in secondary contact between two clades by multiple migrations from various regions of the Nansei Islands.