How plankton deal with their boom-bust lifestyle

Salp mitochondrial genome, recombination.

Citation:

Goodall‐Copestake, W. P. (2016). One tunic but more than one barcode: evolutionary insights from dynamic mitochondrial DNA in Salpa thompsoni (Tunicata: Salpida). Biological Journal of the Linnean Society. DOI: 10.1111/bij.12915

A tunicate with a trick up its sleeve!

Salps are jelly-like plankton that can form dense blooms under favourable ecological conditions. In parts of the Southern Ocean, these blooms can be so large that salps outnumber other plankton including the iconic and abundant Antarctic krill. To gain a deeper understanding of Antarctic salps, genetic variation of the most numerous Southern Ocean salp species (Salpa thompsoni) was assessed by analysing a specific region of the mitochondrial genome called the ‘DNA barcode’. Results from this work have not only provided an insight into salp genetic diversity but also evidence for a process that is thought to be very rare in animals: mitochondrial DNA recombination. The potential significance of this discovery is illustrated here by deSciphered. It is noteworthy because it represents one of the best-illustrated examples of how mitochondrial DNA recombination may be linked to the life history and ecology of an animal species.

The article abstract:

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“The DNA barcode within the mitochondrial cox1 gene is typically used to assess the identity and diversity of animals under the assumption that individuals contain a single form of this genetic marker. This study reports on a novel exception from the pelagic tunicate Salpa thompsoni Foxton. Oozoids caught off South Georgia and the Antarctic Peninsula generated barcodes consisting of a single prominent DNA sequence with some additional, subtler signals of intra-individual variation. Further investigation revealed this was due to duplicated and/or minicircular DNAs. These could not simply be explained as artefacts or nuclear copies of mitochondrial DNA, but provided evidence for heteroplasmy arising from a dynamic mitochondrial genome. Genetic variation of this sort may allow S. thompsoni to ecologically benefit from asexually driven population blooms without incurring the genetic cost of an excessive mutational load. Analysis of the prominent barcode sequence data yielded low haplotype (h < 0.61) and nucleotide (π < 0.0014) diversities, and no evidence for genetic structure between sampling locations as assessed using analysis of molecular variance. These results are consistent with the impact of population blooms and the mixing effect of Southern Ocean currents on S. thompsoni genetic diversity.”