A new study that looked at gut length variation between cichlid fish species found that some of the genetic loci for the trait are sex-specific even though males and females of the same species have the same gut length. The work supports a scenario of "sexual conflict," where gut length differences evolved under different pressures for males and females of the same species and could have implications for the understanding of gut length evolution more generally.
"Gut length is an incredibly important trait for animals, and there are consistent trends across different groups of animals where carnivores tend to have short guts, and herbivores tend to have long guts," says Reade Roberts, associate professor of biological sciences at North Carolina State University and corresponding author of the research.
"However, almost nothing is known about the genetic basis of these differences, in part because it is a very hard trait for genetic mapping studies."
The researchers used two closely related species of cichlid found in central Africa's Lake Malawi - one an omnivore and one a carnivore - to do their genetic comparisons. The two species only diverged around a million years ago, so they remain very closely related even though certain traits, such as gut length, have diversified.
The researchers compared carnivore, omnivore and herbivore cichlid species to a hybrid carnivore/omnivore population to determine the genetic loci, or locations on the chromosomes, that correspond to gut length. They identified some loci that had the same effect on gut length regardless of sex. However, they also saw that different genetic loci impacted males and females differently across the species, even though males and females of each species had roughly the same gut length.
"The question now is why is there a genetic variant only active in females or males," Roberts says.
The answer could have to do with the differing dietary pressures for male and female cichlids of each species.
For example, male cichlids are territorial, remaining in one place during their lives and are subject to varying food availability, while females range more widely. But females undergo regular periods of starvation because they hold their offspring in their mouths until they reach maturity.
"It could be dietary pressure, it could be hormonal - we don't know," Roberts says. "Male versus female bodies are almost like different environments, so you may need different parts of the genome to activate to get the same results. The exciting piece here is that if we hadn't considered sex in this study we wouldn't have found the majority of the loci for gut length."
The research also has potential implications for human health.
"The basic questions - how did these differences arise and what do they mean for health outcomes - will lead to a better understanding of genetic pathways and what they're doing, which could inform future human biomedical research," Roberts says.
The work appears in Genetics and was supported by an Arnold and Mabel Beckman Foundation Young Investigator Award; the National Science Foundation under award IOS-1456765; the U.S. Department of Agriculture under award USDA-NIFA-SCRI 2020-51181-32156; and the National Institutes of Health under award R35 GM147107. Aldo Baez, postdoctoral researcher at NC State, is first author.
-peake-
