Aphids are insects that feed on plants. Their success as crop pests is mainly due to their high demographic and adaptation capacities in relation with their variation in reproductive modes. The “SexAphid” project aims at identifying and characterizing the loci, sequences and genes responsible for a key adaptive trait: the reproductive mode variation. A pluridisciplinary approach - based on genetic, functional genomics and ecology - will tackle this variation in reproductive mode which largely influences the risk of aphid outbreaks on a wide range of cultivated plants.

Aphids are insect pests that are capable of two reproductive modes: an asexual viviparous reproduction, clonal, rapid and efficient during spring and summer, and an oviparous sexual reproduction, in autumn, that allows genetic combinations. The eggs made from this sexual mode are cold-resistant and allow survival during hard winters. The populations that alternate of reproductive modes are called “CP” (Cyclical Parthenogenesis) and can combine the two advantages of being clonal (short term adaptation) and sexual (long term adaptation). This capacity of aphids to alternate between reproductive modes is however sometimes lost in aphid populations: such populations are no more able to produce eggs and might disappear if winter temperatures are low; such populations are called “OP” (“Obligate Parthenogenesis”). Climate plays a key role on the distribution between those two types of populations: populations still able to produce sexual individuals will have an advantage under continental climates, whereas populations that have lost the capacity to produce sexual individuals will have an advantage under warmer climates. For temperate climates, both types of populations can co-exist, with different occurrences from one year to another, depending on the winter temperatures.

SexAphid aims at:

1. Characterizing and identifying the loci and gene functions that differentiate sexual and asexual populations,
2. Assessing the frequency distribution of sexual and asexual populations in the last 15 years, in relation with climatic periods, in particular winter temperatures.

SexAphid focuses on the pea aphid Acyrthosiphon pisum for which a lot of genomics and genetics data and tools are already available. A previous work already identified a genomic zone covering 10 cM of the X chromosome as being very linked to the CP/OP phenotype. We aim to restrict this zone and to define the genomic loci that are tightly linked with the phenotype of interest, and to point out candidate genes. The functions of those candidate genes will be deeply studied by spatio-temporal expression analyses in different sexual and/or asexual populations. Genome editing techniques such as CRISPR-CAS9 will allow testing the precise roles of some of the candidate genes in the control of OP/CP phenotype. These polymorphic characterizations will be used to DNA-type and track wild populations on the pea aphid, captured during the last 15 years, and archived in the lab, in order to test for the presence of correlations between sexual/asexual population frequencies and winter temperatures. As aphids are pest for crops, this work should pave the road for the future development of tools to predict and prevent aphid infestation, in order to improve insect pest management. Our hypothesis is that winter temperature increase in a temperate climate might favor the development of asexual populations and thus increase the damage caused by aphids to crops.