Transposable elements and introgression introduce genetic variation in the invasive ant Cardiocondyla obscurior

Abstract

Introduced populations of invasive organisms have to cope with novel environmental challenges, while having reduced genetic variation caused by founder effects. The mechanisms associated with this "genetic paradox of invasive species" has received considerable attention, yet few studies have examined the genomic architecture of invasive species. Populations of the heart node ant Cardiocondyla obscurior belong to two distinct lineages, a New World lineage so far only found in Latin America and a more globally distributed Old World lineage. In the present study, we use population genomic approaches to compare populations of the two lineages with apparent divergent invasive potential. We find that the strong genetic differentiation of the two lineages began at least 40,000 generations ago and that activity of transposable elements (TEs) has contributed significantly to the divergence of both lineages, possibly linked to the very unusual genomic distribution of TEs in this species. Furthermore, we show that introgression from the Old World lineage is a dominant source of genetic diversity in the New World lineage, despite the lineages' strong genetic differentiation. Our study uncovers mechanisms underlying novel genetic variation in introduced populations of C. obscurior that could contribute to the species' adaptive potential.

Late-life fitness gains and reproductive death in Cardiocondyla obscurior ants

“…Remaining reads were aligned using hisat2 (version 2.1.0) to the newest version of the genome (Cobs.2.1., Errbii et al, 2021 ). Putative splice sites were obtained using gffread (version 0.12.1), and the extensive transposable elements annotation v.2.1 ( Errbii et al, 2021 ) was considered for the mapping procedure. Samtools (version 1.9) was used to sort and convert.sam into .bam files.…”

De novosequencing, diploid assembly, and annotation of the black carpenter ant,Camponotus pennsylvanicus, and its symbionts by one person for $1000, using nanopore sequencing

“…Less accurate identification may explain the lower percentage found in the Florida Carpenter ant (27%) vs. its close relative, the black carpenter ant studied here (34%). However, repeat element content can be low in ants, with two lineages of the heart node ant, Cardiocondyla obscurior , both having 21% repeat content(27).…”

Maternal control over caste allocation in the ant Cardiocondyla obscurior

“…Cardiocondyla is unique among the Formicidae due to the evolution of wingless fighter males and the repeated loss of the winged male morph across the genus [15]. Because colonies of C. obscurior can be easily reared and manipulated, the species has been used to address questions in diverse biological contexts [22,23], ranging from genome evolution [13,24], to social behavior [25], aging [26,27], symbiosis [28,29], and phenotypic plasticity [17,30,31]. In this respect, C. obscurior has been considered a “gold mine” (E. Abouheif pers.…”

“…C. obscurior is a cosmotropical tramp ant [12], with a very streamlined genome (∼193MB, [13]), the smallest ant genome known to date. Adult queens and workers differ in size and morphology and workers lack ovaries.…”

“…Larvae develop via three larval instars which can be distinguished by the shape of the body and the degree of sclerotization of the mandibles [14]. The ants used in this study were all from the Old World lineage [13], maintained in the lab since 2010. Stock colonies were kept in a climate chamber under a 12h/12h and 22°C/26°C night/day cycle at 70% humidity.…”