Genetica (2007) 129:127–132 DOI 10.1007/s10709-006-9009-5 ORIGINAL PAPER All stressed out and nowhere to go: does evolvability limit adaptation in invasive species? An introduction to the symposium at the SSE/ASN/SSB meeting, June 2004 George W. Gilchrist Æ Carol Eunmi Lee Received: 11 January 2006 / Accepted: 16 June 2006 / Published online: 19 August 2006 Ó Springer Science+Business Media B.V. 2006 Abstract Introduced and invasive species are major Species introductions and their subsequent range threats native species and communities and, quite expansions have shaped the biogeography of our pla- naturally, most scientists and managers think of them net throughout the history of life. But recently, changes in terms of ecological problems. However, species in human activity have accelerated long-distance introductions are also experiments in evolution, both transport of organisms, greatly increasing the fre- for the alien species and for the community that they quency of colonization and inviting the establishment colonize. We focus here on the introduced species and invasion of non-native populations. Global chan- because these offer opportunities to study the proper- ges in nutrient cycles and climate may further facilitate ties that allow a species to succeed in a novel habitat the establishment of non-native species by disrupting and the constraints that limit range expansion. More- established patterns of community dynamics and cre- over, an increasing body of evidence from diverse taxa ating ecological opportunities for the invader (Dukes suggests that the introduced species often undergo and Mooney 1999). Introduced and invasive species are rapid and observable evolutionary change in their new also among the top contemporary causes of damage to habitat. Evolution requires genetic variation, which native species and extant biological communities may be decreased or expanded during an invasion, and (Pimentel et al. 2000). Although—quite natu- an evolutionary mechanism such as genetic drift or rally—many researchers think of introduced and natural selection. In this volume, we seek to under- invading species largely in ecological or management stand how natural selection produces adaptive evolu- terms, recent studies demonstrate that significant evo- tion during invasions. Key questions include what is the lution occurs over ecological time scales (reviewed in role of biotic and abiotic stress in driving adaptation, Lee 2002; Stockwell et al. 2003) in a diverse range of and what is the source of genetic variation in plants, invertebrates, and vertebrates. Many of these introduced populations. cases of contemporary evolution focus either on evo- lution of invaders (Gilchrist et al. 2004; Hendry et al. Keywords Adaptation Æ Biological invasion Æ 1996; Johnston and Selander 1964; Lee et al. 2003; Genetic variation Æ Phenotypic plasticity Æ Evolution Stearns 1983) or on the evolution of native species in response to an invader (Carroll and Boyd 1992; Carroll et al. 1997). G. W. Gilchrist (&) We organized this symposium, entitled ‘‘All stressed Department of Biology, College of William & Mary, out and nowhere to go: does evolvability limit adap- Box 8795, Williamsburg, VA 23187-8795, USA e-mail: [email protected] tation in invasive species?’’ to begin an exploration of the mechanisms by which adaptive evolution in re- C. E. Lee sponse to ecological stress takes place during coloni- Wisconsin Institute of Rapid Evolution, Department of zation and invasion events. For close to a century, Zoology, University of Wisconsin, 430 Lincoln Drive, Madison, Wisconsin 53706, USA biological invasions have been regarded as ‘‘experi- e-mail: [email protected] ments in nature’’ (Grinnell 1919), offering opportuni- 123 128 Genetica (2007) 129:127–132 ties for evolutionary biologists to observe a species as it tion can be imposed by abiotic or biotic stress caused enters a new habitat, expands its range, and adapts to by a novel or changing environment encountered new biotic and abiotic conditions. A research agenda during the spread of an invading species. Much of the based on contemporary observations of introduced research featured in this volume uses natural experi- species was first outlined at a symposium organized by ments—species introductions—to understand these C. H. Waddington in 1963, at Asilomar CA. The fundamental factors in evolution. Although our focus resulting volume, ‘‘The Genetics of Colonizing Spe- is on contemporary evolution, at some point in its cies’’ (Baker and Stebbins 1965), contains many papers history every species has been introduced into a novel that have become citation classics. Waddington argued environment and has faced many of the same stresses that selection on an established non-native species that modern colonizing species encounter but often at would occur when that species encountered stressful a slower rate. environment conditions during range expansion. Key questions that we have asked our authors to Observations of evolution during biological invasions address here include: thus offer a unique opportunity to assess the rate (Darwin 1859; Hendry and Kinnison 1999; Simpson 1. Where does the genetic variation that fuels adap- 1944) and repeatability (Cooper et al. 2003; Gould and tive evolution come from? Introduced species may Eldredge 1977; Losos et al. 1998) of natural selection. undergo bottlenecks that could either reduce or Furthermore, evolutionary studies of invasions provide enhance the amount of additive genetic variation much needed information for ecologists and managers (VA) available for selection. Canalization may seeking to understand ways to predict and mitigate the conceal a reservoir of genetic variation that is expansion of invasive species. expressed only upon encountering a novel stress. Waddington (1965) focused on evolvability, the New genotypes and traits may be assembled ability of a population to adapt in response to envi- through hybridization. ronmentally induced stress, as a function of the de- 2. How does genetic architecture influence the gree of canalization or plasticity of ecologically evolvability of a species? In particular, what can we important traits. The phenotypic variants targeted by learn about the interaction between genotype and natural selection may or may not produce an evolu- phenotype in the source population that may pre- tionary response to selection, depending on the ge- dispose a particular lineage to be a successful col- netic architecture of the underlying traits. By genetic onist? Do plastic responses enable successful architecture, we mean the nature and number of colonization? Does plasticity change during intro- genes, their pattern of regulation, and their domi- ductions? nance, epistatic, and pleiotropic interactions that 3. How does environmental stress, either abiotic or influence a particular adaptation. Highly canalized biotic, influence the evolutionary trajectory of architectures imply that the developmental program species? Do patterns of evolution in the introduced may allow only a small number of discrete phenotypic population that parallel patterns in the ancestors states. Such systems limit the possible directions of arise because of similar selection pressures or be- evolution but may allow a more rapid response to cause of genetic canalization (i.e. parallel genetic selection because the alternative genetic and devel- mechanisms: Hoekstra et al. 2004)? Does the rate opmental pathways are already in place and only a of adaptation to environmental stress determine minor transcriptional change might be needed to shift range limits? the phenotype (Suzuki and Nijhout 2006; West-Eb- erhard 2003; Wray et al. 2003). In contrast, highly In the pages that follow, we will provide a brief plastic architectures producing copious continuous summary of the papers and try to highlight the topics variation in traits may allow a more precise fit be- above that were most prominently addressed by the tween trait and environment (Huey et al. 2003) and authors. thus, by reducing selective deaths and expanding the range of expressed genetic variation, plasticity could accelerate evolution (Waddington 1953; West-Eber- Genetic variation and biological invasions hard 2003) Alternatively, plastic responses could blunt the blade of selection, potentially retarding evolution Although natural populations generally seem to have (de Jong 2005; Wright 1931). The degree to which abundant genetic variation and significant evolutionary natural systems conform to any of these extremes is a potential (Kingsolver et al. 2001), it must be the case subject of current debate. In any case natural selec- that at least some traits under selection may lack 123 Genetica (2007) 129:127–132 129 variation in the dimension required for adaptation. In Recombinational hybridization and speciation has the case of species introductions, a small founding led to the formation of hybrid sunflower species colo- population may suffer further reduction in ecologically nizing extreme habitats. The hybrid species Helianthus important genetic variation. Species introductions, anomalus, Helianthus deserticola,andHelianthus par- however, may provide opportunities for hybridization adoxus are much more limited in geographic distribu- and the acquisition of new genes. Many papers in this tion than their parents, and occur in desert, sand dune, volume provide evidence of altered levels of genetic and saline wetland habitats, respectively. Field exper- variation in invading populations. iments demonstrated