|MEZA-LAZARO, RUBI - Autonomous National University Of Mexico|
|POTEAUX, CHANTAL - University Of Paris|
|BAYONA-VÁSQUEZ, NATALIA - University Of Georgia|
|ZALDÍVAR-RIVERÓN, ALEJANDRO - Autonomous National University Of Mexico|
Submitted to: Mitochondrial DNA, Part A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2018
Publication Date: 1/31/2018
Citation: Meza-Lazaro, R.N., Poteaux, C., Bayona-Vásquez, N.J., Branstetter, M.G., Zaldívar-Riverón, A. 2018. Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae). Mitochondrial DNA, Part A. http://dx.doi.org/10.1080/24701394.2018.1431228.
Interpretive Summary: Mitochondrial DNA (mtDNA) sequences are commonly used for studying relationships among species and populations in animals. These sequences tend to be particularly useful for delimiting species because they are fast evolving, maternally inherited, and show little evidence of recombination. Unfortunately, there is growing evidence that multiple copies of mitochondrial genes or genomes can occasionally exist in the same organism and this can be problematic for studies investigating species boundaries or relationships among species. The prevalence of having multiple copies of mitogenomes in the same individual is not well known for most organismal groups, but next-generation sequencing has made it much easier to detect the phenomenon. In this study, we used next-generation sequencing (Illumina platform) to investigate mitogenome structure and the prevalence of mitochondrial heteroplasmy (multiple copies present) in ants of the Ectatomma ruidum complex. We sequenced 21 worker ants from four putative morphospecies and assembled a total of 24 unique mitogenomes. The data revealed that several individuals had multiple mitogenomes present, providing the first evidence of extensive heteroplasmy in ants. The exact cause of the heteroplasmy could not be determined with confidence, but all mitogenome copies appeared to be functional. Additionally, we used the data to examine species boundaries and found support from phylogenetic analyses for the existence of three previously proposed, but not described, biological species. Our results show that mitochondrial heteroplasmy occurs in ants and that it may be a more common feature in animals than previously thought.
Technical Abstract: Recent advances in DNA sequencing and polymorphism detection technology have made it possible to test for the existence of more than one type of organellar genome within a cell or individual (heteroplasmy). Here we investigated whether the origin of mitochondrial (mt) DNA polymorphism in members of the E. ruidum (Roger) complex is due to nuclear mt paralogs, heteroplasmy or recombination. We obtained 24 assembled mitogenomes from 21 worker individuals generated with shotgun Illumina sequencing and byproducts of ultraconserved element enriched genomic libraries of specimens assigned to four morphospecies and putative hybrids of the E. ruidum complex (E. ruidum spp. 1-4 and 2x3) and E. tuberculatum (Olivier). Mitogenomes from specimens of E. ruidum spp. 3, 4 and 2x3 had a considerable number of polymorphic sites across all their genes. Polymorphic protein coding genes do not show function lost signals. Phasing haplotypes of the cytochrome oxidase I (cox1) and cytochrome b (cob) genes for specimens of the above taxa showed strong evidence for purifying selection, confirming the presence of two functional mitochondrial genomes. Reciprocal monophyly and high genetic distances based on the mt protein coding genes support the delineation of the three previously proposed species for the E. ruidum complex. Our results demonstrate for the first time the existence of extensive heteroplasmy in ants, and highlight the need of similar studies across diverse taxa to better understand the origin and extent of this phenomenon in metazoans.