CE02 - Terre vivante

Evolution of the genetic load during biological invasions – GENLOADICS

Evolution of the genetic load during biological invasions

An evolutionary paradox characterizes many biological invasions: a striking ecological success despite a drastic reduction in genetic diversity. Could the genetic load be the key to explain this observation?

Comparison of genetic load between native and invasive populations

Biological invasions are a major component of global change. Yet it is still not understood why some introduced populations are invasive and others are not. Among the most interesting hypotheses is the purging of the genetic load (i.e. elimination of the deleterious mutations) during the introduction process. After the introduction of a small number of individuals into the future invaded area, high levels of inbreeding and genetic drift lead to the exposure of deleterious mutations to natural selection, which can theoretically lead to their purging. This mechanism could be at the origin of the ecological success of invasive species.<br />The GENLOADICS project proposes to test the genetic load purging hypothesis on a large taxonomic scale - about ten non-model insect species - via population genomics approaches. After sequencing key populations of these different species, we will identify polymorphism, particularly within the coding part of the genome (the exome), and then quantify and compare the genetic load of native and invasive populations.<br />This project will provide an almost definitive answer to the purge hypothesis in invasion biology, and will be a major technical opening to study the evolution of the genetic load in a wide range of organisms of interest (e.g. biological control agents, livestock, endangered species).

The measurement of life history traits that is typically considered to test the purge hypothesis is extremely difficult to implement. It requires working on living populations, which is difficult, or even impossible for some species. Today, high-throughput sequencing methods theoretically make it possible to compare the frequencies of deleterious or potentially deleterious mutations between populations on any species. We propose to test the purge hypothesis on a large taxonomic scale - 10 non-model insect species. To do this, we will use a full-genome sequencing approach on several populations of each species. We will then focus on the coding regions of the genome to quantify and compare the genetic load of native, invasive and spatially expanding populations.

Ongoing project

Ongoing project

Ongoing project

Biological invasions are a major component of global change. Yet it is still not understood why some introduced populations are invasive and others are not. Among the most interesting hypotheses is the purging (i.e. elimination) of deleterious mutations during the introduction process. Deleterious mutations constitute what is called the genetic load because they are responsible for a decrease in the fitness of individuals by accumulating in the genome over time. After the introduction of a small number of individuals into the future invaded area, high levels of inbreeding and genetic drift lead to the exposure of deleterious mutations to natural selection. This can have two consequences: the decrease of the average fitness of the population and the purging of deleterious mutations. The assumption we make is that the populations that will actually become invasive are those that have purged part of their deleterious alleles. Indeed, they will have a major evolutionary advantage because they will be less subject to inbreeding depression and will thus better tolerate the low densities encountered during the establishment phase and during any secondary introductions. On the other hand, theory suggests that the genetic load that has not been purged could then become fixed on the fronts of geographic expansion by genetic drift (we use the expression "expansion load"), and thus compromise the success of the invasion in the longer term.
The measurement of life history traits that is typically considered to test such hypotheses is extremely difficult to implement. It requires working on living populations, which is difficult, or even impossible for some species. Today, high-throughput sequencing methods theoretically make it possible to compare the frequencies of deleterious or potentially deleterious mutations between populations on any species. We propose to test the purge hypothesis on a large taxonomic scale - 10 non-model insect species. To do this, we will use an exon capture protocol developed in our laboratory and suited to non-model species, and then we will quantify and compare the genetic load of native, invasive and spatially expanding populations.
The objective of this project will be both a technical and scientific first: (i) application of a protocol to capture exomes and compare genetic loads generalizable to non-model species, (ii) testing the hypotheses of deleterious allele purging and expansion load on key populations of a large number of invasive species. This project will provide an almost definitive answer to the purge hypothesis in invasion biology and will constitute a very important technical opening for studying the evolution of the genetic load in a variety of organisms of interest (e.g. biological control agents, domestic animals, threatened species).

Project coordination

Eric Lombaert (INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE - Centre PACA - Institut Sophia Agrobiotech)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

INRA PACA - ISA INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE - Centre PACA - Institut Sophia Agrobiotech

Help of the ANR 345,816 euros
Beginning and duration of the scientific project: December 2019 - 48 Months

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