Characterization of the complete mitochondrial genome of the invasive tramp ant Cardiocondyla obscurior (Hymenoptera: Formicidae: Myrmicinae)

Comparative mitogenomic analysis provides evolutionary insights into Formica (Hymenoptera: Formicidae)

Formica is a large genus in the family Formicidae with high diversity in its distribution, morphology, and physiology. To better understand evolutionary characteristics of Formica, the complete mitochondrial genomes (mitogenomes) of two Formica species were determined and a comparative mitogenomic analysis for this genus was performed. The two newly sequenced Formica mitogenomes each included 37 typical mitochondrial genes and a large non-coding region (putative control region), as observed in other Formica mitogenomes. Base composition, gene order, codon usage, and tRNA secondary structure were well conserved among Formica species, whereas diversity in sequence size and structural characteristics was observed in control regions. We also observed several conserved motifs in the intergenic spacer regions. These conserved genomic features may be related to mitochondrial function and their highly conserved physiological constraints, while the diversity of the control regions may be associated with adaptive evolution among heterogenous habitats. A negative AT-skew value on the majority chain was presented in each of Formica mitogenomes, indicating a reversal of strand asymmetry in base composition. Strong codon usage bias was observed in Formica mitogenomes, which was predominantly determined by nucleotide composition. All 13 mitochondrial protein-coding genes of Formica species exhibited molecular signatures of purifying selection, as indicated by the ratio of non-synonymous substitutions to synonymous substitutions being less than 1 for each protein-coding gene. Phylogenetic analyses based on mitogenomic data obtained fairly consistent phylogenetic relationships, except for two Formica species that had unstable phylogenetic positions, indicating mitogenomic data are useful for constructing phylogenies of ants. Beyond characterizing two additional Formica mitogenomes, this study also provided some key evolutionary insights into Formica.

De novo assembly of the complete mitochondrial genome of Mycetophylax simplex Emery, 1888 through organelle targeting revels no substantial expansion of gene spacers, but rather some slightly shorter genes

Mitochondria play a key role in cell biology and have their own genome, residing in a highly oxidative environment that induces faster changes than the nuclear genome. Because of this, mitochondrial markers have been exploited to reconstruct phylogenetic and phylogeographic relationships in studies of adaptation and molecular evolution. In this study, we determined the complete mitogenome of the fungus-farming ant Mycetophylax simplex (Hymenoptera, Formicidae) and conducted a comparative analysis among 29 myrmicine ant mitogenomes. Mycetophylax simplex is an endemic ant that inhabits sand dunes along the southern Atlantic coast. Specifically, the species occur in the ecosystem known as "restinga", within the Atlantic Forest biome. Due to habitat degradation, land use and decline of restinga habitats, the species is considered locally extinct in extremely urban beaches and is listed as vulnerable on the Brazilian Red List (ICMBio). We employed a mitochondrion-targeting approach to obtain the complete mitogenome through high-throughput DNA sequencing technology. This method allowed us to determine the mitogenome with high performance, coverage and low cost. The circular mitogenome has a length of 16,367 base pairs enclosing 37 genes (13 protein-coding genes, 22 tRNAs and 2 rRNAs) along with one control region (CR). All the protein-coding genes begin with a typical ATN codon and end with the canonical stop codons. All tRNAs formed the fully paired acceptor stems and fold into the typical cloverleaf-shaped secondary structures. The gene order is consistent with the shared Myrmicinae structure, and the A + T content of the majority strand is 81.51%. Long intergenic spacers were not found but some gene are slightly shorter. The phylogenetic relationships based on concatenated nucleotide and amino acid sequences of the 13 protein-coding genes, using Maximum Likelihood and Bayesian Inference methods, indicated that mitogenome sequences were useful in resolving higher-level relationship within Formicidae.

Complete Nucleotide Sequence of the Mitogenome of Tapinoma ibericum (Hymenoptera: Formicidae: Dolichoderinae), Gene Organization and Phylogenetics Implications for the Dolichoderinae Subfamily

The ant Tapinoma ibericum Santschi, 1925 is native to the Iberian Peninsula. This species, as well as other species from the Tapinoma nigerrimum complex, could form supercolonies that make these species potentially invasive and could give rise to pests. Recently a mature colony from this species has been found in the Isle of Wight (United Kingdom). Mitogenomes have been used to study the taxonomy, biogeography and genetics of species, improving the development of strategies against pest invasion. However, the number of available mitogenomes from the subfamily Dolichoderinae is still scarce and only two of these mitogenomes belong to Tapinoma species. Herein, the complete mitogenome of T. ibericum is presented in order to increase the molecular information of the genus. The T. ibericum mitogenome, retrieved by Next-Generation Sequencing data, is 15,715 bp in length. It contains the typical set of 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNAs and the A + T-rich control region. Comparisons of the T. ibericum mitogenome with other dolichoderine mitogenomes revealed the existence of four gene rearrangements in relation with the ancestral insect mitogenome. One of these rearrangements, involving the tRNA-Ile, tRNA-Gln and tRNA-Met genes, was found in most of the analyzed ant mitogenomes. Probably this rearrangement was an ancestral or plesiomorphic character in Formicidae. Interestingly, another rearrangement that affects to tRNA-Trp, tRNA-Cys and tRNA-Tyr genes was found only in Tapinoma species. This change could be a synapomorphic character for the genus Tapinoma, and could be used as a phylogenetic marker. Additionally, a phylogenetic analysis was performed using the protein-coding gene sequences from available Dolichoderinae mitogenomes, as well as mitogenomes from representative species from other Formicidae subfamilies. Results support the monophyletic nature of the genus Tapinoma placing it within the same clade as the rest of Dolichoderinae species.

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

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.

Complete mitochondrial genome of the acrobat ant Crematogaster teranishii Santschi, 1930 (Formicidae; Hymenoptera)

The genus Crematogaster is a diverse group of ants found around the world. We have completed the mitochondrial genome of Crematogaster teranishii, which is the first mitochondrial genome of the genus. The mitochondrial genome is 17,442 bp long and 20.3% in GC ratio, which is similar to those of other ants. It contains 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, and a control region with same gene order to other myrmicine species. The intergenic region between nad3 and trnA was unusually long compared to other ant species. Phylogenetic analysis showed that C. teranishii was closely related to other members of tribe Crematogastrini.