"Junk" DNA Predicts Body Size in Seed Shrimp

Caption:  An ostrocod or “seed shrimp” (Photo credit: Anna33 at English Wikipedia [GFDL, CC-BY-SA-3.0 or CC BY 2.5], via Wikimedia Commons)

It turns out that size does matter, say researchers in the Department of Integrative Biology who have discovered that the size of a tiny sea creature’s genome may influence its body size.

A genome is the entire set of DNA and genes that an animal possesses - but not all of this DNA has an obvious purpose. For example, up to 98% of the human genome has no known function. The mystery surrounding the presence of non-coding, or “junk”, DNA is formally referred to by biologists as the “C-value enigma.” 

Dr. Ryan Gregory and his research team are spearheading attempts to find out the purpose of junk DNA, where it comes from, and why it is so abundant. The team has worked with flies, hummingbirds, and now seed shrimp in order to find out if there is a relationship between amount of junk DNA and traits such as body size, metabolism, and development.

“Grasshoppers have genomes five to six times larger than humans,” says Gregory.  “It raises interesting questions about what’s going on.”

In the case of seed shrimp—tiny crustaceans just 1 to 3 mm in size—genome size seems to influence body size. Gregory and his team looked at 46 seed shrimp species and found that the larger the genome, the bigger the seed shrimp. It follows a similar pattern to what has been observed in other animals with determinate growth – that is, animals that grow in body size by increasing their cell volumes rather than the number of cells. Larger genomes may lead to increased cell sizes, which might explain how genome size could predict eventual body size for some animals.

In contrast, Gregory and his team found no relationship between genome size and habitat type of the seed shrimp, as marine and freshwater species did not differ significantly in their genome size. However, genome size may still influence other traits that have not yet been investigated, such as life span.

According to Gregory, junk DNA can provide insights into the degree that noncoding DNA influences the growth and development of many animals. Some forms of noncoding DNA can influence the expression of other genes while others have no apparent function at all, yet it appears that even the presence of apparently non-functional DNA can still affect many biological traits. He and his lab will remain at the forefront of probing the C-value enigma as they continue to explore the genomes of ever more diverse animals to unravel the secrets of junk DNA.

“I get to work from the genome up [animals] and from the genome down [genes]… there’s a lot of diversity doing this kind of work,” says Gregory.

This research was funded by the National Sciences and Engineering Research Council of Canada (NSERC), the National Science Foundation, the Research Mentorship Program, and the Australian Museum.

Read the full article in the Journal of Heredity.

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