Is Evolution Necessary for Range Expansion? Manipulating Reproductive Timing of a Weedy Annual Transplanted beyond Its Range

Abstract

Ecologists often consider how environmental factors limit a species' geographic range. However, recent models suggest that geographic distribution also may be determined by a species' ability to adapt to novel environmental conditions. In this study, we empirically tested whether further evolution would be necessary for northern expansion of the weedy annual cocklebur (Xanthium strumarium) in its native North American range. We transplanted seedlings beyond the northern border and photoperiodically manipulated reproductive timing, a trait important for adaptation to shorter growing seasons at higher latitudes within the range, to determine whether further evolution of this trait would result in a phenotype viable beyond the range. Earlier reproductive induction enabled plants to produce mature seeds beyond the range and to achieve a reproductive output similar to those grown within the range. Therefore, evolution of earlier reproduction in marginal populations would be necessary for northward range expansion. This study is the first to empirically show that evolution in an ecologically important trait would enable a species to survive and reproduce beyond its current range. These results suggest that relatively few traits may limit a species' range and that identifying evolutionary constraints on such traits could be important for predicting geographic distribution.

Interactions between Soil Habitat and Geographic Range Location Affect Plant Fitness

“…replacement) at both sites in the beyond edge region, the 95% confidence intervals of seed production included values below one (not shown), indicating that even these populations, though best-adapted to this region, may not maintain themselves here based on data from this year of study. This is consistent with other studies that find adaptation of populations to conditions at the range edge, though absolute fitness below that necessary to sustain the populations when transplanted beyond the range edge [38], [39]. By contrast, other studies have not found a reduction in fitness beyond the range edge [40]–[42].…”

Evolutionary constraints on adaptive evolution during range expansion in an invasive plant

“…(b) Implications for species distributions and range limits Genetic constraints on local adaptation have often been invoked to explain geographical range limits, but there are few empirical tests of this hypothesis (Bradshaw 1991;Davis & Shaw 2001;Blows & Hoffman 2005). Constraints on traits that determine the timing of reproduction may be particularly important in preventing range expansion to environments with shorter growing seasons typical of high latitudes and altitudes (Griffith & Watson 2006), and also in response to anthropogenic changes in climate and seasonality (Bradshaw & Holzapfel 2001;Franks et al 2007). Studies on a wide range of plant and animal species have compared levels of diversity at neutral maker loci between geographically central versus peripheral populations and many have found evidence of a decline in genetic variation towards range margins (reviewed in Eckert et al 2008).…”

“…Etterson & Shaw 2001;Griffith & Watson 2006). A fitness trade-off between two traits occurs if natural selection cannot simultaneously improve both traits (Lande 1979;Lande & Arnold 1983).…”

Reduced pollinator service and elevated pollen limitation at the geographic range limit of an annual plant

“…Empirical studies of range limits using experiments (e.g., Geber and Eckhart 2005, Griffith and Watson 2006, Angert et al 2008, Kellermann et al 2009) and species distribution models (in the context of climate change [Thomas et al 2004, Lenoir et al 2008, Jiguet et al 2010) have mainly evaluated putative limiting abiotic factors (but see Samis and Eckert 2009). Empirical studies of range limits using experiments (e.g., Geber and Eckhart 2005, Griffith and Watson 2006, Angert et al 2008, Kellermann et al 2009) and species distribution models (in the context of climate change [Thomas et al 2004, Lenoir et al 2008, Jiguet et al 2010) have mainly evaluated putative limiting abiotic factors (but see Samis and Eckert 2009).…”