Nav: Home

Baby fish exercising, a surprising source of adaptive variation in fish jaws

August 01, 2017

AMHERST, Mass. - An unspoken frustration for evolutionary biologists over the past 100 years, says Craig Albertson at the University of Massachusetts Amherst, is that genetics can only account for a small percentage of variation in the physical traits of organisms. Now he reports experimental results on how another factor, a "bizarre behavior" that is part of early cichlid fish larvae's developmental environment, influences later variation in their craniofacial bones.

Albertson has studied African cichlid fish for 20 years as a model system for exploring how biodiversity originates and is maintained, with a focus on genetic contributions to species differences. In a new series of experiments with former Ph.D. student Yinan Hu, now a postdoctoral fellow at Boston College, they examined a "vigorous gaping" behavior in larval fish that starts immediately after the cartilaginous lower jaw forms and before bone deposition begins. Results appear in the current early online issue of Proceedings of the Royal Society B.

As Albertson explains, "We predicted that the baby fish are exercising their jaw muscles, which should impose forces on the bones they attach to, forces that might stimulate bone formation." Albertson and Hu observed that gaping frequency, which could reach as high as 200 per minute, varied by species "in a way that foreshadows differences in bone deposition around processes critical for the action of jaw opening."

Albertson, an evolutionary geneticist, says, "For over a hundred years, we've been taught that the ability of a system to evolve depends largely on the amount of genetic variation that exists for a trait. What is ignored, or not noted for most traits, is that less than 50 percent of genetic variation can typically be accounted for by genetics." He adds, "Variation in skull shape is highly heritable, so why can we only find genetic variability that accounts for such a small amount of variability in bone development? In my lab we have shifted from elaborating our genetic models to looking more closely at the interaction between genetics and the environment."

How the environment influences development is known as epigenetics in its original and broadest meaning, Albertson points out. Coined in the 1940s to mean anything not encoded in the nucleotide sequence, it has narrowed to refer to how the 3D structure of the DNA molecule is modified, he notes. "That meaning is true, but it isn't the only one. We're returning to the original definition."

In this sense, gaping is part of "a very dynamic developmental environment," Albertson notes. "Bones are not forming in static lumps of tissue. Rather, they are developing as part of, and perhaps in response to, a highly complex and dynamic system." The fact that species differ in gaping rate led the researchers to test the idea that differences in bone development could be accounted for by variation in this behavior. "We performed experiments to see if we could slow the rate in fast-gaping species and speed it up in slow-gaping species, and to see if this behavioral manipulation could influence bone development in predictable ways."

Not only did these experiments work, but the magnitude of difference in skeletal morphology induced by these simple shifts in behavior was similar to those predicted to be caused by genetic factors. Albertson says, "What I find really exciting is that in 15 years of manipulating the genetics of craniofacial bone development we can account for up to 20 percent of the variability, so it's modest. When we manipulate gaping behavior, we can influence developmental variability by about 15 percent, which is comparable, almost equal to the genetic response."

The geneticist adds, "When I give talks, this is what surprises colleagues the most, that the environmental effect is on par with the genetic effect, and that it is not systemic but highly specific to important bones involved in fish feeding."

Alberston says this behavior makes sense because "Nature is all about efficiency. Fine-tuning an adaptive response to a particular niche increases the chances of survival. Sometimes longer bones are better, and one way to get there is to kick-start the bone developmental program. This gaping behavior precedes bone formation, so it may represent a way to increase efficiency by setting an animal on the trajectory toward an adaptive phenotype earlier."

He adds, "This is just the beginning. Our field has been entrenched in a gene-centered view of evolution for nearly a century. My hope is that this study adds to a growing body of literature that shows there are other important sources of variation. I hope we can expand the paradigm to consider the environmental context where development takes place, because the effects are likely greater and more widespread than we'd predict."

The next step for his lab will be to figure out how environmental stimuli influence development, Albertson explains. "We now need to understand how bone cells sense and respond to their mechanical environment. What are the molecules that enable this mechano-sensing?"

To this end, the researchers demonstrated that mechanical-load-induced shifts in skeletal development are associated with differences in expression of the ptch1 gene, implicated previously in mediating between-species skeletal shap differences. "That the same molecule is involved in mechano-sensing within species and genetic divergence between species is very cool as it's consistent with evolutionary theory," Albertson says.

The idea is that when an animal population is exposed to a new environment, certain molecules will enable them to respond by conforming their bodies to meet new challenges. If the new environment is stable, natural selection should favor genetic mutations in these molecules that fix the original, transient response. This theory establishes a framework for the initial steps in species divergence. "We think that we now have a molecular foothold into this process," Albertson explains. "These are exciting times."
-end-


University of Massachusetts at Amherst

Related Genetic Variation Articles:

Poor anti-VEGF responses linked to genetic variation in immune regulation
Though reducing VEGF signaling with anti-VEGF therapies has positive effects in many patients with wet age-related macular degeneration, some individuals continue to experience vision deterioration during treatment.
Out of sync: How genetic variation can disrupt the heart's rhythm
New research from the University of Chicago shows how deficits in a specific pathway of genes can lead to the development of atrial fibrillation, a common irregular heartbeat, which poses a significant health risk.
New insights into human genetic variation revealed: Nature paper
A powerful new analysis of the protein-coding region of the human genome known as the exome will boost efforts to pinpoint clinically relevant genetic variations linked to human disease.
Defining the consequences of genetic variation on a proteome-wide scale
Combining two emerging large-scale technologies for the first time -- multiplexed mass spectrometry and a mouse population with a high level of natural genetic diversity --researchers at Harvard Medical School (HMS) and The Jackson Laboratory (JAX) can crack an outstanding question in biology and medicine: how genetic variants affect protein levels.
RNA splicing mutations play major role in genetic variation and disease
RNA splicing is a major underlying factor that links mutations to complex traits and diseases, according to an exhaustive analysis of gene expression in whole genome and cell line data.
Genetic variation shown in patients with severe vascular complications of infection
Major infections such as influenza and bacterial sepsis kill millions of people each year, often resulting from dangerous complications that impair the body's blood vessels.
Genetic variation may explain Asian susceptibility to Kawasaki disease
Scientists from the RIKEN Center for Integrative Medical Sciences (IMS) in Yokohama, Japan, in collaboration with researchers from a number of hospitals around Japan, have found two variations in a gene called ORAI1, one of which may help explain why people of Asian descent are more susceptible to Kawasaki disease, a poorly understand ailment that mostly afflicts young children.
Enormous genetic variation may shield tumors from treatment
The most rigorous genetic sequencing ever carried out on a single tumor reveals far greater genetic diversity among cancer cells than anticipated, more than 100 million distinct mutations within the coding regions of its genes.
Genetic variation is key to fighting viruses
Using a genome-wide association study, EPFL scientists have identified subtle genetic changes that can cause substantial differences to how we fight viral infections.
Poor survival in multiple myeloma patients linked to genetic variation
Researchers have found that multiple myeloma patients with a genetic variation in the gene FOPNL die on average 1-3 years sooner than patients without it.

Related Genetic Variation Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Anthropomorphic
Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#SB2 2019 Science Birthday Minisode: Mary Golda Ross
Our second annual Science Birthday is here, and this year we celebrate the wonderful Mary Golda Ross, born 9 August 1908. She died in 2008 at age 99, but left a lasting mark on the science of rocketry and space exploration as an early woman in engineering, and one of the first Native Americans in engineering. Join Rachelle and Bethany for this very special birthday minisode celebrating Mary and her achievements. Thanks to our Patreons who make this show possible! Read more about Mary G. Ross: Interview with Mary Ross on Lash Publications International, by Laurel Sheppard Meet Mary Golda...