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We study the evolution of spreading populations -- both the colonizing populations of invasive species and the spreading edge of native distributions undergoing range expansion.
RANGE EXPANSION ON MULTIPLE CONTINENTS
RANGE EXPANSION ON MULTIPLE CONTINENTS
In the Anthropocene, both native species tracking climate change and exotic species invading new continents are rapidly expanding their ranges. Forecasts of these range dynamics are greatly complicated by the potential for rapid evolution of more dispersive phenotypes and adaptation to novel abiotic and biotic conditions. While native and exotic range expansions have many similarities, they are expected to subject populations to different types of environmental gradients, levels of genetic variation, and gene flow. We are exploring these different evolutionary drivers of range expansion by taking advantage of a species currently engaged in both types of spread: Dittrichia graveolens (L.) Greuter, a Mediterranean annual plant from the Asteraceae family that is expanding its European native range northward, while it is also rapidly invading California.
To study evolution during range expansion in D. graveolens, we have grown plants from seeds collected at the core and edge of the European and California ranges in a greenhouse common garden study spanning two generations of plants. Phenotypic traits we are measuring include flowering phenology, plant height, fecundity, seed size, and seed head morphology. To complement our phenotypic data, we are conducting a whole-genome sequencing study of all 450 maternal families in collaboration with Dr. Rachel Meyer. Along with a newly developed reference genome for D. graveolens, these data will allow us to identify signatures of selection, population structure, and genomic diversity patterns, and link these to traits showing phenotypic differentiation. This research is funded by a USDA NIFA grant #2020-67013-31856.
D. graveolens has demonstrated remarkably rapid spread in both Europe and California in recent decades.
Even though the native range expansion coincided with recent climate change in Northwest Europe, previous work has shown that rapid evolution of earlier flowering in more seasonal climates in the north likely contributed to this spread. We are conducting a habitat suitability modeling study for D. graveolens with historical and current climate data to answer two questions:
Did D. graveolens simply track climate change in Europe, or did the species' climate niche evolve over the course of range expansion?
How does taking into account the recent range expansion in Europe change invasion forecasts in California?
INVASION GENETICS & GENOMICS
INVASION GENETICS & GENOMICS
An interesting feature of biological invasions is that introduced species necessarily go through founding events, yet they can be remarkably successful, despite predicted reductions in genetic diversity and the constraints these might place on evolutionary potential. One possible resolution to this paradox is that multiple introductions and subsequent gene flow may be essential for allowing invasive species to adapt to environmental challenges.
Early work from our lab led by PhD student/postdoc Katrina Dlugosch documented that losses of molecular variation are significant and substantial (15-20%) on average, though they are not ubiquitous. As predicted, allelic richness showed greater losses than heterozygosity, and multiple introductions did cause a significant but small reduction in the degree of molecular diversity that is lost. However, in a companion review of studies of quantitative traits, we found almost no evidence of a loss of diversity in the morphological or life history traits that would be the target of most adaptive evolution.
Katrina's dissertation work on the novel invader Hypericum canariense L. (Hypericaceae) showed substantial loss of neutral genetic variation yet adaptive evolution of life history traits and phenology.
For more details see:
Dlugosch, KM, & IM Parker. 2008. Invading populations of an ornamental shrub show rapid life history evolution despite genetic bottlenecks. Ecology letters, 11(7), 701-709.
Dlugosch, KM, & IM Parker. 2008. Founding events in species invasions: genetic variation, adaptive evolution, and the role of multiple introductions. Molecular ecology, 17(1), 431-449.
Dlugosch, KM & IM Parker, 2017. Evolutionary Ecology, Introduction. In Barrett, Colautti, Dlugosch, and Rieseberg, Invasion Genetics: The Baker and Stebbins Legacy.
You can find publications from these projects and more at Ingrid's Google Scholar page.
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