Extensive mitochondrial heteroplasmy in the neotropical ants of the Ectatomma ruidum complex (Formicidae: Ectatomminae)

Abstract

We assembled mitogenomes from 21 ant workers assigned to four morphospecies (E. ruidum spp. 1-4) and putative hybrids of the Ectatomma ruidum complex (E. ruidum spp. 2x3), and to E. tuberculatum using NGS data. Mitogenomes from specimens of E. ruidum spp. 3, 4 and 2 × 3 had a high proportion of polymorphic sites. We investigated whether polymorphisms in mitogenomes are due to nuclear mt paralogues (numts) or due to the presence of more than one mitogenome within an individual (heteroplasmy). We did not find loss of function signals in polymorphic protein-coding genes, and observed strong evidence for purifying selection in two haplotype-phased genes, which indicate the presence of two functional mitochondrial genomes coexisting within individuals instead of numts. Heteroplasmy due to hybrid paternal leakage is not supported by phylogenetic analyses. Our results reveal the presence of a fast-evolving secondary mitochondrial lineage of uncertain origin in the E. ruidum complex.

Keywords:

• Mitochondrial genome
• Formicidae
• heteroplasmy
• paternal leakage
• numts
• phasing haplotypes
• hymenoptera

Acknowledgements

We thank Javier Ponce and Dmitry Dubovikoff for donating some of the examined specimens; Cristina Mayorga and Guillermina Ortega for their assistance at the CNIN IB-UNAM, Laura Márquez and Gabriela Camacho for assistance in the laboratory, Susana Guzmán for taking the digital picture of the Ectatomma specimen and to Travis C. Glenn from UGA for library prep and sequencing support. Part of the bioinformatic work was carried out using the supercomputer resources given by the Dirección General de Cómputo y de Tecnologías de la Información (DGTIC-UNAM) through the project LANCAD-UNAM-DGTIC-339. USDA is an equal opportunity provider and employer.

Disclosure statement

The authors report no conflicts of interest.

Additional information

Funding

This study was funded by grants given by the Consejo Nacional de Ciencia y Tecnología (CONACyT, Mexico, Proyecto SEP-Ciencia Básica no. 220454; Proyecto de cooperación internacional SEP-CONACyT-ANUIES no. 207562), UNAM (PAPIIT-DGAPA convocatoria 2016, proyecto no. IN207016) to AZR, and the US National Science Foundation (NSF, DEB#1354739, Project ADMAC). RNML was supported by CONACyT and a DGAPA-UNAM postdoctoral fellowships to carry out this work.