Hybridization and adaptation of Helicoverpa spp. in the Brazilian agriculture landscape

Abstract

Helicoverpa armigera is an invasive pest in Brazil. The wide geographic distribution and polyphagia of H. armigera promote its simultaneous occurrence with other endemic Heliothinae species of the Americas, which previously evolved allopatrically. Ecological interactions such as reproductive interference, host range, hybridization and introgression between the invasive and the native species are key events in the colonization of invasive organisms into new ecosystems. We will study these phenomena in the economically devastating crop pests Helicoverpa armigera, which has recently invaded and may be hybridizing with a native species Helicoverpa zea in Brazil. We will conduct temporal and geographic monitoring of the invasion across a large scale using a novel sequencing approach (haplotagging sequencing) to obtain genomic data for a large sample of populations of both species, which will allow us to address the following questions: What is the age of the hybridization event and is there evidence for multiple sources of invaders and what are the genetic consequences of hybridization for the two species. In order to achieve these goals, we will first access the high-quality genome assemblies for both species and generate a high number of markers in H. armigera and H. zea populations from Brazil. The two species have diverged in allopatry for over a million years, so genetic differences between them mean that we will have considerable power to identify blocks in the genomes of both species that have resulted from genetic mixing between the species (introgression). The size and distribution of these blocks provide information about the time since hybridization. We will also determine whether there is evidence for incompatibilities between the two genomes that would help to maintain their distinctiveness in the face of mixing through hybridization by looking for genetic combinations that are under-represented in hybrids. In contrast, regions that are more common than expected by chance would indicate adaptive introgression. This is likely for genes involved in adaptation to local conditions in Brazil that may move into the invasive species or genes for insecticide resistance that is likely to move into the native species from the invader. Finally, we will search for signatures of recent adaptation in both species' populations, which might be indicative of genomic regions involved in host adaptation, insecticide resistance or other traits of potential economic importance. In particular, H. armigera has developed resistance to a far wider range of insecticides and host species as compared to H. zea, so there is potential for further introgression of alleles that could precipitate host range expansion and insecticide resistance in H. zea. In contrast, H. zea is adapted to local conditions in Brazil and might lend alleles that facilitate local adaptation to the invasive H. armigera populations. Here, we are proposing to sequence around 800 Helicoverpa individuals sampled between 2014 to 2022 in multiple locations throughout Brazil with the objectives of understanding the demographic and adaptative processes of H. armigera invasion in Brazil and assessing the contribution of the hybridization with H. zea in these processes. The project will uncover patterns that will be of immediate application in the control of this pest, for example, the forewarning of the arrival of the invader into new areas and identifying characteristics such as insecticide resistance than could be transferred between the two species. In addition, we will address fundamental questions related to speciation biology, such as the nature of the genomic incompatibilities that keep species distinct. (AU)