Invasion genetics

Invasion genetics is the area of study within biology that examines evolutionary processes in the context of biological invasions. Invasion genetics considers how genetic and demographic factors affect the success of a species introduced outside of its native range, and how the mechanisms of evolution, such as natural selection, mutation, and genetic drift, operate in these populations. Researchers exploring these questions draw upon theory and approaches from a range of biological disciplines, including population genetics, evolutionary ecology, population biology, and phylogeography. Invasion genetics, due to its focus on the biology of introduced species, is useful for identifying potential invasive species and developing practices for managing biological invasions. It is distinguished from the broader study of invasive species because it is less directly concerned with the impacts of biological invasions, such as environmental or economic harm. In addition to applications for invasive species management, insights gained from invasion genetics also contribute to a broader understanding of evolutionary processes such as genetic drift and adaptive evolution.

History

Descriptions of invasive species Charles Elton formed the basis for examining biological invasions as a unified issue in his 1958 monograph, The Ecology of Invasions by Animals and Plants, drawing together case studies of species introductions. Other important events in the study of invasive species include a series of issues published by the Scientific Committee on Problems of the Environment in the 1980s and the founding of the journal Biological Invasions in 1999. Much of the research motivated by Elton's monograph is generally identified with invasion ecology, and focuses on the ecological causes and impacts of biological invasions.

The Genetics of Colonizing Species

The evolutionary modern synthesis in the early 20th century brought together Charles Darwin's theory of evolution by natural selection and classical genetics through the development of population genetics, which provided the conceptual basis for studying how evolutionary processes shape variation in populations. This development was crucial to the emergence of invasion genetics, which is concerned with the evolution of populations of introduced species. The beginning of invasion genetics as a distinct study has been identified with a symposium held at Asilomar in 1964 which included a number of major contributors to the modern synthesis, including Theodosius Dobzhansky, Ernst Mayr, and G. Ledyard Stebbins, as well as scientists with experience working in areas of weed and pest control. Stebbins, working with another botanist, Herbert G. Baker, collected a series of articles which emerged from the Asilomar symposium and published a volume titled The Genetics of Colonizing Species in 1965. This volume introduced many of the questions which continue to motivate research in invasion genetics today, including questions about the characteristics of successful invaders, the importance of a species' mating system in colonization success, the relative importance of genetic variation and phenotypic plasticity in adaptation to new environments, and the effect of population bottlenecks on genetic variation.

Terminology of invasion genetics

Since its publication in 1965, The Genetics of Colonizing Species helped to motivate research which would provide a theoretical and empirical foundation for invasion genetics. However, the term invasion genetics only first appeared in the literature in 1998, and the first published definition appeared in 2005. The success of introduced species is quite variable, consequently researchers have sought to develop terminology which allows distinguishing different levels of success. These approaches rely on describing invasion as a biological process.

Process of biological invasion

Background Researchers have proposed a number of different methods for describing biological invasions. In 1992, the ecologists Mark Williamson and Alastair Fitter divided the process of biological invasion into three stages: escaping, establishing, and becoming a pest. Since then, there has been an expanding effort to develop a framework for categorizing biological invasions in terms that are neutral with respect to a species' environmental and economic impacts. This approach has allowed biologists to focus on the processes which facilitate or inhibit the spread of introduced species. David M. Richardson and colleagues describe how introduced species must pass a series of barriers prior to becoming naturalized or invasive in a new range. Alternatively, the stages of an invasion may be separated by filters, as described by Robert I. Colautti and Hugh MacIsaac, so that invasion success would depend on the rate of introduction (propagule pressure) as well as the traits possessed by the organism.

Description The most recent systematic effort to describe the steps of a biological invasion was made by Tim Blackburn and colleagues in 2011, which combined the concepts of barriers and stages. According to this framework, there are four stages of an invasion: transport, introduction, establishment, and spread. Each of these stages is accompanied by one or more barriers.

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