Mutations in Corals Passed on to Offspring Could Save Endangered Species

According to a study, somatic mutations in corals are passed on to their progeny and help endangered coral species adapt to and survive climate change.

Corals have been found to transmit somatic mutations or DNA sequence changes that occur in non-reproductive cells, to their progeny, challenging more than a century's worth of evolutionary dogma.

The discovery, made by an international team of researchers led by biologists from Penn State, suggests a potentially new pathway for the generation of genetic diversity, the building block for evolutionary adaptation.

This pathway may be crucial for enabling endangered corals to adapt and survive rapidly changing conditions in their environment.

Genetic Mutation for Most Animals

Iliana Baums, a professor of biology at Penn State, said that the genetic underpinnings of a trait, like growth rate, must be passed down from one generation to the next for that trait to evolve. The research is led by Baums.

Baums explained that for the majority of animals, new genetic mutations could only influence evolution if they happen in reproductive or germline cells, such as an egg or sperm cell. Because they are not passed down to offspring, mutations that take place in the somatic cells of the rest of the body were once believed to be irrelevant to evolution. Corals, though, seem to have found a way around this restriction that permits them to defy this evolutionary principle.

Since Darwin's time, we have learned more and more specific information about evolution. The DNA sequence of an organism heavily influences its traits. The DNA sequences of individuals within a population vary, and this genetic variation can result in variations in traits, like body size, that may give an individual a reproductive advantage.

It is only rarely that a new genetic mutation arises that gives a person such a reproductive advantage, and evolution can only move forward if-and this is crucial-the person can pass the mutation on to its progeny.

Kate Vasquez Kuntz, a graduate student from Penn State, said that in the majority of animals, body cells and reproductive cells are separated early in development. Kuntz is the co-lead author of the study.

Kuntz pointed out that the only genetic changes that can affect how a species evolves are those that take place in its reproductive cells. Given how quickly climate change is occurring, this slow process of watching for rare mutations in a specific set of cells can be problematic.

For some organisms, such as corals, the separation of reproductive cells from other cells, however, may take place later in development or may never take place at all, providing a route for genetic mutations to spread from the body of a parent to its offspring. That would also increase genetic diversity and might even act as a system for "pre-screening" advantageous mutations.

Corals

Corals can reproduce sexually by producing sperm and egg cells as well as asexually through budding and colony fragmentation. Eggs from one coral colony are typically fertilized by sperm from a different colony for the Elkhorn corals that were the subject of this study, which broadcast their sperm and egg cells into the water during spawning events.

However, the study group discovered that some Elkhorn coral eggs produced live offspring without the assistance of a second coral, resembling a single-parent sexual reproduction.

Sheila Kitchen, a postdoctoral researcher from the California Institute of Technology and Penn State, said that by reducing the number of genetic possibilities that could exist in the offspring, single-parent reproduction made it possible for the team to more quickly look for possible somatic mutations originating from the parent coral and trace them into the offspring. Kitchen is another co-lead author of the study.

Read also: Is Traffic Calming the Key to Robust Coral Reefs? 

Genetic Mutation Through Somatic Mutation

The research team genotyped samples from ten different locations on a sizable Elkhorn coral colony that had produced single-parent offspring as well as samples from five nearby colonies at nearly 20,000 genetic locations, using a microarray to investigate DNA distinctions between the samples.

The results showed that all six samples were clones derived from a single original colony through asexual reproduction and colony fragmentation, meaning any genetic variation would have been caused by somatic mutation.

The researchers studied coral offspring and found that 50% of their somatic mutations had been inherited from their parents. The exact mechanism of how they make their way into germline cells in the corals is still unknown, but scientists suspect incomplete cell segregation may be the cause.

Baums explained that corals form colonies of genetically identical polyps, which allows for the screening of somatic mutations that arise in a single coral polyp without necessarily affecting the colony as a whole.

As the coral colony expands, cells with potentially damaging mutations may disappear while cells with potentially advantageous mutations may flourish and spread. As we have now shown, if these mutations are then passed down to offspring, corals may have an additional tool to hasten their resilience to climate change, Phys Org reports.

Related article: Corals That Experience Heat Stress are More Likely to Tolerate High Water Temperatures