With the rise of global commerce and with remarkable biogeographic similarities, southeastern Asia and the southeastern United States have become a major conduit for exchange of species that have become invasive in their respective introduced habitats. Such biological invasions represent a pressing conservation problem across the globe. Population genetics can provide a powerful forensic tool for understanding the geographic distribution of invasive species, including the history of invasion and the likely sites of origin within the native range. Since it is difficult to move potentially invasive species between countries, the PIRE program allows us to establish a collaboration among researchers in the U.S., China, Hong Kong and Taiwan. Through a partnership between the University of Georgia, Georgia Southern University, the USDA-Southern Research Station, Nanjing University, Nanjing Forestry University, Taiwan National University, Academia Sinica, the University of Hong Kong and the Chinese Academy of Sciences, this award supports research to provide a robust phylogeographic and demographic baseline for ten target plant and pathogen species: half native to southeastern Asia and invasive in the U.S. and half native to the southeastern U.S. and invasive in China, Taiwan and Hong Kong.
In support of PIRE goals to build a robust and sustainable international partnership and to develop a diverse, globally-engaged U.S. science and engineering workforce, this PIRE program will implement a multi-tiered program to develop a generation of students and faculty committed to continuing work on invasive species in the U.S. and China, Taiwan and Hong Kong. The grant combines an undergraduate study abroad experience and a graduate training program to establish a multi-tiered pipeline development program. The program gets undergraduates prepared and excited about Asia by introducing them to Chinese language and culture, then completing field and laboratory work in China, Taiwan and Hong Kong. Those undergraduates are encouraged to enter doctoral programs in the life sciences. Graduate students enter the pipeline and are given the language and research tools to conduct work in China, Taiwan and Hong Kong. Postdocs and faculty enter the pipeline last, but the PIRE program provides them with the contacts to initiate and continue collaborations with international partners. Outreach to the community and K-12 schools in the U.S. and abroad is a key component of the program.
This project is co-funded with the Division of Environmental Biology in the Directorate for Biological Sciences.
Global trade has opened the world to the possibility of exchange of species that never had the means or opportunity to move expansive distances. Some of the introductions of species across the globe have been intentional, but others have occurred without intent. Some of those introductions have been innocuous, as species transported far from their native habitats have not thrived in their new homes. But some species, for unknown reasons, grow extraordinarily well in new habitats; so much that they grow beyond control with significant deleterious impact. These invasive species are so destructive that most of us can readily observe their impact. Surprisingly, we do not know exactly why some species have this resounding advantage and in many cases, the study of these species is constrained by the fact that we have to study them both where they are native and where they are invasive. In this project, we have been studying the invasion history of a number of species that are native to Asia and invasive in the United States, including species like kudzu, wisteria, Chinese privet and citrus greening disease. Global trade is a two-way street; increased trade to Asia has provided an avenue for a number of species native to the U.S. to become invasive in Asia and we have been studying those species as well, including goldenrod, pokeweed, mosquitofish and Geranium. We now have a fundamental understanding of the process of invasion for 7 different plant and animal species that are either native to the southeastern United States and invasive in eastern Asia (mosquitofish, pokeweed, Geranium, goldenrod) or native to eastern Asia and invasive in the southeastern U.S. (kudzu, wisteria, privet). Geranium carolinianum is a winter annual herb native to North America and invasive in China. In the native range, genetic diversity was higher and structure was lower than expected. In China, our results provided evidence for multiple introductions near Nanjing with subsequent range expansion to the west and south. Patterns of genetic diversity across China reveal weak founder effects that are driven largely by low-diversity populations at the expansion front, away from the introduction location. This suggests that reduced diversity in China has resulted from successive founder events during range expansion, and that the loss of genetic diversity in the Nanjing area was mitigated by multiple introductions from diverse source populations. We also detected a signature of adaptation to colder, drier winters in China. Within countries, strong multivariate adaptation appears to be driven by latitudinal climatic variation in the US, but not in China. Additionally, adaptive trait combinations as well as their underlying correlations differ between the two countries, indicating that adaptation in invasive populations does not parallel patterns in native populations due to differences in selection pressures, genetic constraints, or both. Mosquitofish, Gambusia affinis, were intentionally introduced into Hawaii as early as 1905 and then spread from there throughout Taiwan, the Philippines, Japan, and China over the next few decades. With this historical backdrop, we reconstructed the invasion history of G. affinis using genetic markers for 20 localities throughout Asia. We found a decrease in the number of haplotypes present and heterozygosity compared to the native range. However, our tests for a recent bottleneck were negative suggesting that the introductions could have been large or have had sufficient time to recover. We assigned 19 of the localities back to a single native population and also found a mitochondrial haplotype unique to that locality that was found in ~73% of the individuals from the introduced range. This native population is the closest sampled locality to the recorded source population. Surprisingly, our results demonstrate that the historical record for mosquitofish introductions to Asia is quite complete and accurate. Mosquitofish introduced to Asia were likely the result of a single introduction event from the recorded source population near Seabrook, Texas. To reconstruct the full invasion history of kudzu we screened over 5000 individuals from the US and Asia for the same genetic markers. Preliminary data suggests that there were five separate introductions into the United States from both Japan and China. We have also asked the question of whether or not kudzu was on Japan prior to its separation of the Chinese mainland. There was no evidence of a genetic bottleneck in Japan, which is a common product of colonization. In fact, Japan had the highest number of chloroplast haplotypes than Korea or China. Thus, it appears that Japan may be a genetic hotspot for diversity and was not a product of ancient colonization. Our project has trained a large number of undergraduate and graduate students with a deep understanding, not only of science, but also of Chinese language and culture that will allow them to work exceedingly well in international collaborations.
