Adaptive introgression in the Anthropocene

Human translocation of species and anthropogenic climate change are resulting in some of the fastest rates of species distribution changes ever seen, causing many native and non-native species to be brought together. While the ecological consequences are often well-documented, the evolutionary impacts of hybridization and gene flow between native and non-native species are usually less visible. Yet gene flow between native and non-native species could profoundly affect future evolutionary adaptations and diversification, potentially impacting on species conservation, responses to climate change and the spread of invasive species. Previous studies have only focussed on gene flow between a few exemplar species. So we lack a general understanding of the prevalence and impact of interspecific gene flow across the tree of life, and specifically of how human activities may be altering these rates of gene flow.

In this ambitious proposal, we will leverage reference genomes produced by the Darwin Tree of Life project and combine high-throughput sequencing with the latest bioinformatic methods to address a major question of growing importance: What is the extent of gene flow between native and non-native flowering plant species, and is this gene flow of adaptive value to native or non-native species? We will for the first time assess gene flow across a major branch of the tree of life using all 106 native/non-native flowering plant species pairs known to be hybridising in the British Isles. We will then use these data to parameterise models predicting the rate of gene flow between native and non-native species, and test model estimates of cryptic gene flow among species pairs that have not been observed to hybridize. The British flora is intensively studied, and its well characterised distributions, hybrids and ecology make it an ideal model system to build predictive models exploring ecological and genetics factors affecting the rates and effects of gene flow between native and non-native species.

Over the course of this project we will generate 24 trillion bases of sequence data, comprising the genomes of 741 individuals from 269 flowering plant species (137 native, 132 non-native). We will use this data to first assess the extent of gene flow between all 106 native/non-native flowering plant species pairs that are known to hybridise in the British Isles (Objective 1), and establish whether the recent range expansions seen in some of these species are associated with increased gene flow (Objective 2). Population samples will then be used to assess evidence for adaptive gene flow in a subset of 10 recipient species that from Objective 1 and 2 show indications of adaptive introgression (Objective 3). We will use the estimates of introgression from Objectives 1 and 2 to build statistical models to understand the genetic and ecological factors affecting gene flow (Objective 4). Finally, we will test assess the accuracy of model predictions of cryptic gene flow between species that are not known to hybridize using additional empirical estimates of gene flow from 17 genera of Asteraceae (daisy family) and Poaceae (grasses) (Objective 5).

This project will be a major step towards understanding the evolutionary consequences of human-mediated gene flow between species. Interspecific hybridization could well be widespread, yet gene flow may still be restricted because of postzygotic reproductive barriers. Alternatively, gene flow between species may be common, and with strong fitness consequences. In addition to academic beneficiaries (evolutionary and global change biologists), our results will inform conservation practitioners, control of invasive species, and increase awareness in the general public about the ubiquity and importance of gene flow among species, and evolutionary responses to environmental change.