CleanAllAFLP

All sampled population AFL

All_Amb_CoordEnv_26July2012

All Ambrosia occurrences in the French Alp

Pop Info 6Sept2012

Description of the sampled population

AllDataCG_29Oct12

All trait measured in the common garde

Is There Any Evidence for Rapid, Genetically-Based, Climatic Niche Expansion in the Invasive Common Ragweed?

<div><p>Climatic niche shifts have been documented in a number of invasive species by comparing the native and adventive climatic ranges in which they occur. However, these shifts likely represent changes in the realized climatic niches of invasive species, and may not necessarily be driven by genetic changes in climatic affinities. Until now the role of rapid niche evolution in the spread of invasive species remains a challenging issue with conflicting results. Here, we document a likely genetically-based climatic niche expansion of an annual plant invader, the common ragweed (<i>Ambrosia artemisiifolia</i> L.), a highly allergenic invasive species causing substantial public health issues. To do so, we looked for recent evolutionary change at the upward migration front of its adventive range in the French Alps. Based on species climatic niche models estimated at both global and regional scales we stratified our sampling design to adequately capture the species niche, and localized populations suspected of niche expansion. Using a combination of species niche modeling, landscape genetics models and common garden measurements, we then related the species genetic structure and its phenotypic architecture across the climatic niche. Our results strongly suggest that the common ragweed is rapidly adapting to local climatic conditions at its invasion front and that it currently expands its niche toward colder and formerly unsuitable climates in the French Alps (i.e. in sites where niche models would not predict its occurrence). Such results, showing that species climatic niches can evolve on very short time scales, have important implications for predictive models of biological invasions that do not account for evolutionary processes.</p></div

Location of the 27 populations sampled for the genetic analysis.

<p>Populations are presented in (a) the geographic space, plotted over a map of the mean summer temperature and (b) the regional niche space. Each population is represented with a pie chart showing the average proportion of the genetic clusters inferred from structure in each population. The populations <i>a priori</i> suspected of adaptation to novel climates are circled in red. For (b) the dark grey dots indicate the position of the 3,888 populations of <i>A</i>. <i>artemisiifolia</i> recorded in the French Alps, used to estimate the regional niche of the species. A blue triangle represents the location of the common garden experiment.</p

Population genetic characteristics along environmental gradients.

<p>Neutral genetic diversity H_e within populations (a) and population-specific genetic differentiation F_ST (b) as a function of the mean summer temperature experienced by each sampled populations. The populations <i>a priori</i> suspected of adaptation to novel climates are plotted in red.</p

Phenotypic variance and integration across the species' niche as captured by the temperature gradient.

<p>The three panels represent different features of the so-called phenotypic <b><i>G</i></b> matrix (i.e. the traits genetic variances and co-variances). (a) The relation between <b><i>G</i></b><i>'s</i> volume (i.e. total genetic variance) per population and the temperature gradient. (b) The relationship between <b><i>G</i></b><i>'s</i> shape (proportion of variance explained by <i>Pmax)</i> and the temperature gradient. (c) The relationship between the population potential response to selection toward colder and low levels of solar radiation, and two regional niche axes: temperature (in °C) and solar radiation (in kWH/m²; only considering population of the coldest half of the gradient). The size of the dots represents the mean absolute trait displacement after application of the Selection Skewer Method, and the red arrow indicates the direction of the applied selection vector.</p

Four examples of strong correlations between estimated population AFLP marker frequency and estimated population functional trait value (correlation coefficient > 0.8).

<p>The first line (a-b) shows two correlations between the population predicted allelic frequency with the predicted plant height, and the second line (c-d) shows two correlations with the predicted plant biomass. In the upper right corner of the four graphics is represented the allele environment relationship (T: temperature, R: radiation).</p

Relationship between each of the four functional traits measured in common garden and the two axes of regional niche gradients.

<p>The two environmental gradients are mean summer temperature and mean annual solar radiation. Curves were estimated from generalized mixed effect models taking into account the population structure and the experimental design random effects. The black dots represent the mean trait value for each population.</p