The Earth is home to millions of species that all look different. Some species that look more similar still have differences between them. Even within each species, individuals may look similar but are still not identical.
These similarities and differences in organisms are due to their genes, which contain the DNA. The combined differences in the DNA of individual species make up their genetic diversity.
What is Genetic Diversity?
Genetic diversity refers to the range of various inherited traits within a species or the total number of characteristics in the genetic makeup of a species. It measures how often two bits of DNA from the exact genomic location differ within a population.
The DNA comprises bases attached to their backbones to make the nucleotides. Genetic diversity can be expressed as nucleotide diversity or the percentage of positions within the genome where two individuals from a given species are expected to have different DNA bases. Genetic diversity also affects the long-term survival of a species since it allows the organisms to adapt when the environment changes.
Several factors can affect the genetic diversity of a species, such as mutation rate, population size, and population stability. The higher the mutation rate, the more genetic changes a species acquires, and the greater its genetic diversity will be. On the other hand, larger populations provide more copies of a genome that creates genetic diversity, while smaller people lead to lower genetic diversity.
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What is the Most Genetically Diverse Species?
According to a 2015 study by Maria A. Baranova and her colleagues, the split gill mushroom (Schizophyllum commune) has up to 20% nucleotide diversity. This is considered the greatest genetic diversity reported for any eukaryotic organism.
This means that two different split gill mushrooms will have other DNA bases at about 20 out of 100 positions in their genomes. The previous record holder, the roundworm Caenorhabditis brenneri, reported a nucleotide diversity of 14.1%.
Both the split gill mushroom and Caenorhabditis brenneri are considered to be genetically hyperdiverse, which means that they have a nucleotide diversity that is greater than 5%. Most species of plants and animals have nucleotide diversities below that value. For reference, humans have a genetic diversity of only 0.1%.
The split gill mushroom can also be found in all continents except Antarctica, giving it a very effective population size on the order of millions. Furthermore, this organism has an unusually high mutation rate, about ten times that of the fruit fly Drosophila melanogaster. The high population size and mutation rate likely contribute to the high genetic diversity of split gill mushrooms.
Meanwhile, the hyperdiversity of C. brenneri is attributed to the large effective population size, which is also in millions. This species is found in tropical regions where it eats bacteria in rotting fruit and rotting vegetation, an abundant food resource available for much of the year.
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