We look at what happens when two species breed with each other and produce hybrids. Two evolutionary outcomes are classically recognized:
- the emergence of new hybrid lineages, that sometimes becomes fully independent from their parental taxa and evolve into new species (we refer to homoploid and allopolyploid speciation).
- the transfer of genes (and traits) among species, when the hybrids keep reproducing with one or the other of their parental taxa (we refer to introgression and gene flow).
Introgression – gene flow
Fig. 1. Experimental introgression setup. We combine hybridization with selection to transfer a complex trait (here salt resistance) from one species into another.
Fig. 2. Using next-generation sequencing, we check whether the genes underlying the trait of interest have the same chances to be transferred between species. We then relate these probabilities to functional aspects
We use an experimental evolution setup, based on black mustard and turnip (Brassica nigra and B. rapa), to transfer a complex trait (salt tolerance expressed by B. rapa), via hybridization between the two species (Fig. 1). We then track the introgression process, using next-generation sequencing and check whether the various genes at the origin of salt tolerance have the same chances to get transferred among species (Fig. 2).
Our group has also surveyed (non-adaptive) introgressions in several plant species, including emblematic crops and their wild relatives:
- Pajkovic M., Lappe S., Barman R., Parisod C., Neuenschwander S., Goudet J., Alvarez N., Guadagnuolo R., Felber F., Arrigo N., 2014. Wheat alleles introgress into selfing wild relatives: empirical estimates from approximate Bayesian computation in Aegilops triuncialis. Molecular Ecology 23(20) pp. 5089-5101.
- Parisod C., Definod C., Sarr A., Arrigo N., Felber F., 2013. Genome-specific introgression between wheat and its wild relative Aegilops triuncialis. Journal of Evolutionary Biology 26(1) pp. 223-228.
- Delplancke M., Alvarez N., Espíndola A., Joly H., Benoit L., Brouck E., Arrigo N., 2012. Gene flow among wild and domesticated almond species: insights from chloroplast and nuclear markers. Evolutionary Applications 5(4) pp. 317-329.
- Arrigo N., Gudagnuolo R., Lappe S., Pasche S., Parisod C., Felber F., 2011. Gene flow between wheat and wild relatives: empirical evidence from Aegilops geniculata, Ae. neglecta and Ae. triuncialis. Evolutionary Applications 4(5) pp. 685-695.
- Felber F., Kozlowski G., Arrigo N., Guadagnuolo R., 2007. Genetic and ecological consequences of transgene flow to the wild flora. Advances in Biochemical Engineering-Biotechnology 107 pp. 173-205
Hybridization and diversification
Fig. 3. Character segregation in Silene latifolia x S. dioica hybrids, at the third generation after hybridization. The array of genotypes they cover suggests that hybrid lineages have increased abilities to explore the fitness landscape. These abilities might translate into evolutionary consequences that we quantify using diversification statistics. Picture credits: Anne-Marie Labouche.
We address this simple question: are hybrid lineages benefiting from any evolutionary advantage? Simply looking at character segregation in hybrid descendants (Fig. 1) reveals a wide array of phenotypes that results from the reshuffling of the genetic variation of the parental taxa. This variation is expected to fuel adaptive processes and several classic authors have recognized hybridization as a potential evolutionary trigger (e.g. Lewontin 1966, Stebbins 1969).
We perform meta-analyses, based on publicly available data, to assess the evolutionary benefit of hybridization, over the longer term. We focus on allopolyploids, the largest cohort of hybrid species in plants and check whether hybrid lineages are as much abundant, show lower extinction probabilities and have higher rates of climatic niche evolution than their non-hybrid counterparts :
- Barker M.S., Arrigo N., Baniaga A., Li Z., Levin D.A. (submitted) On the relative abundance of auto- and allopolyploids.
- Arrigo N., Baniaga A., Kong H., Li Z., Barker M.S. (in prep.) Hybridization associated with increased net diversification rates of polyploid plants.
- Arrigo N., de La Harpe M., Litsios G., Zozomová-Lihová J., Španiel S., Marhold K., Barker M.S., Alvarez N. (submitted) Hybridization as a driver of climatic niche evolution in Alyssum montanum (Brassicaceae).
Our research provides many opportunities for intern-ships, first-step and master thesis projects. We also encourage interested post-doc fellows to join us. Our group has a sound expertise in next-generation sequencing and bioinformatics. We also make an extensive use of simulations and approximate Bayesian computation to model and quantify the phenomenons we are dealing with. These skills are typically transferable, also outside of Academia, and we will enjoy sharing them.
P.S. we also grow some fantastic turnips and mustards.