Multicellular organisms including humans have most DNA coiled up within a cell’s nucleus, however a small part is within mitochondria, which are organelles that produce energy and regulate many metabolic processes within a cell.
Nuclear DNA is inherited from both parents, mitochondrial DNA is typically passed down from on generator to the next via the mother. Variations in nucleotide sequence of small mtDNA was assumed to neither affect cell functioning or undergoing of natural selection; and has been thought of as an essential tool on science fields ranging from genetics to climate change to examine evolutionary history and relationships among individuals or groups of organisms.
Growing evidence suggests some mtDNA variants get selected over other under certain circumstances. Researchers have found that mtDNA can be even more subjected to selection than currently believed. Experiments conducted with fruit flies demonstrated how differences in environmental temperatures can influence selection of one mtDNA variant over another, in what is believed to be the first of its kind study to infer the role of thermal selection in shaping of mtDNA frequencies in nature.
Two naturally occurring mtDNA variants were investigated which are carried by fruit flies, one more common in sub-tropic Northern parts where temperatures run warm, and the other more common from the Southern where temperatures tend to be colder. Specimens were collected from two sites in Australia and interbred to produce a series of populations with equally mixed genes, which were divided into four subpopulations which were maintained at different temperatures. Two of the subpopulations were kept at 19 and 25 degrees Celcius, the other two fluctuated to simulate thermal conditions of the two collection sites. After three months mtDNA fo the specimens from all subpopulations was sequenced.
Presence of bacteria such as Wolbachia that affects mtDNA was also examined. Some of the populations were treated with antibiotics to kill off any Wolbachia infections they might be harboring to distinguish their effect.
Flies reared under warm conditions were found to have one of the two mtDNA variants become more common than the other, the same variant was also found to be more prevalent in specimens collected in the warmer Northern areas. Similar pattern was observed in specimens reared in cold conditions. Researchers only observed this effect when Wolbachia infections were removed; and variation patterns in males did not always match up to ones in females.
According to the researchers findings show that temperature shapes how mtDNA varies in nature, and that additional factors such as sex and infection with microbes may influence how mitochondrial genome evolves, but additional studies are required to identify part of the mitochondrial genomes that are sensitive to environmental temperature to understand the mechanisms behind it, and mtDNA should still be used as a genetic tool keeping in mind it evolves in response to thermal environment.
