The complete mitogenome of Isotomurus maculatus: a widespread species that is invading the sub-Antarctic region

Abstract

Isotomurus maculatus (Collembola, Isotomidae) is a springtail with a large distribution. This species has been introduced to the sub-Antarctic Prince Edward Islands. In this study, the mitogenome of I. maculatus was reconstructed. The total length of the mitochondrial genome is 15,263 bp and comprises 13 protein-coding genes, 22 tRNAs, and two rRNAs. The nucleotide composition is 34.4% adenine, 29.2% thymine, 15.1% guanine, and 21.3% cytosine. A Bayesian phylogenetic tree indicates that I. maculatus clusters as the sister taxon to the genus Cryptopygus, with high statistical support.

Keywords:

• Collembola
• springtail
• invasive species
• mitochondrial genome
• Prince Edward Islands

Collembola (springtails) are ubiquitous arthropods with representatives in most terrestrial ecosystems (Carapelli et al. 1995). Springtails are important in ecological systems due to their role in nutrient cycling and as bioindicators of ecosystem health (Rusek 1998; Filser 2002; Seastedt 1984). The geographical distribution of species tend to be dynamic and varies as a result of climatic changes or habitat suitability (Hill et al. 1999; Root et al. 2003). Species belonging to the genus Isotomurus have successfully colonized a wide range of habitats and have tentatively been described from sub-Antarctic oceanic islands. On Marion Island (one of two islands belonging to the Prince Edward Islands), Isotomurus cf. palustris have colonized the entire island, in spite of very low mitochondrial variation at the cytochrome oxidase subunit I gene (Myburgh et al. 2007). This possibly suggests that successful colonization involved only a few founders. This putative species was subsequently classified as Isotomurus maculatus (Greenslade 2010) based on morphological differences, notably the pigmentation pattern on the dorsal side of the animals (Carapelli et al. 2001; Greenslade 2010).

Isotomurus maculatus is a hemiedaphic springtail (lives partly within the soil and partly on the surface; Carapelli et al. 2001) and is a widespread species (Fjellberg 2007; Liu et al. 2012; Greenslade et al. 2013). Here, we report the annotated mitogenome of I. maculatus. This information, when taken with data available for other species (Torricelli et al. 2010; Jagatap et al. 2019; Monsanto et al. 2019) can be used to understand whether a selective adaptive advantage contributes to its success as a widespread species.

Genomic DNA of 16 specimens from the Prince Edward Islands (South African territory) was extracted using the DNeasy Blood and Tissue kit (Qiagen, Germany). Since whole specimens were used for DNA extractions, another specimen from the same locality was deposited as a voucher specimen at the Iziko Museums of South Africa (Voucher No. SAM-ENW-C010312). Genomic libraries were prepared and indexed separately. The libraries were sequenced using the Illumina HiSeq4000 platform (Illumina, USA). The sequencing run produced a total of 66 GB of raw data. The mitogenome was assembled using NOVOPlasty (Dierckxsens et al. 2017) with default settings, except for the insert size that was changed to 350 bp. The reference seed was the COI gene of I. maculatus (accession number: DQ147558; Myburgh et al. 2007). The MITOS2 WebServer (Donath et al. in press) was used to annotate the genome. The protein-coding gene (PCG) boundaries were adjusted using Exonerate v2.2 (Slater and Birney 2005) and the ribosomal RNA boundaries were re-validated in Infernal v1.1 (Nawrocki and Eddy 2013). Each PCG of I. maculatus and nine other arthropods (>68% similarity) was aligned independently. A Bayesian tree was constructed in BEAST v2.5.0 (Bouckaert et al. 2014) using the HKY substitution model (Hasegawa et al. 1985), and 10 million MCMC iterations with a 20% burnin. The tree was visualised in Figtree v.1.4.3 (Rambaut 2016) (Figure 1).

Figure 1 . Bayesian phylogenetic tree of Isotomurus maculatus and nine other species (seven Collembola and two arthropods) with the nodes showing well supported posterior probabilities. The following species were used for the phylogenetic analysis: Isotomurus maculatus MK509021 (Collembola, Isotomidae), Cryptopygus antarcticus NC_010533 (Collembola, Isotomidae), Cryptopygus terranovus NC_037610 (Collembola, Isotomidae), Folsomia candida KU198392 (Collembola, Isotomidae), Folsomotoma octooculata KC862316 (Collembola, Isotomidae), Orchesella cincta NC_032283 (Collembola, Entomobryidae), Orchesella villosa EU016195 (Collembola, Entomobryidae), Gomphiocephalus hodgsoni AY191995 (Collembola, Hypogastruridae), Anopheles stephensi KT899888 (Diptera, Culicidae), Simulium maculatum NC_040120 (Diptera: Simuliidae).

The total length of the circularised mitochondrial genome is 15,263 bp. Typical mitogenomic features (13 PCGs, 22 tRNAs, and two rRNAs) were annotated. The nucleotide composition of the genome is 34.4% adenine, 29.2% thymine, 15.1% guanine, and 21.3% cytosine. Based on available data, Isotomurus maculatus clusters as the sister taxon to the genus Cryptopygus, with high statistical support. The significant divergence between Collembola and other members of the Insecta is also confirmed by our results (Luan et al. 2005; Gao et al. 2008).

Acknowledgements

We thank the Department of Environmental Affairs (South African National Antarctic Programme) who allowed us to collect specimens (permit number 1/2013) and provided logistical support for the voyage. We acknowledge the Centre for High Performance Computing (CHPC) in Cape Town and IT service (University of Johannesburg) for bioinformatics support.

Disclosure statement

The authors report no conflict of interest, and are responsible for the content and writing of this article.

Additional information

Funding

The research was supported by National Research Foundation [NRF SANAP grant to BvV: grant number 110728].