It seems that being a brainiac is just in a dolphin’s genes. That’s the upshot from a paper, published on 27 June in the Proceedings of the Royal Society B, that contains insights from the recently sequenced genome of the bottlenose dolphin (Tursiops truncatus). Researchers say that the results should shed light on the evolution of the dolphin nervous system and reveals commonalities with other large-brained mammals.
“Dolphins are a really interesting model to look at because so much of their morphology is modified,” says Mike McGowen, a postdoctoral fellow in molecular genetics at Wayne State University (WSU) College of Medicine in Detroit, Michigan, and a co-author on the study.
Last fall, a team led by researchers at Baylor College of Medicine in Houston, Texas, took the first crack at sequencing the bottlenose dolphin’s genome, as part of a larger study of several mammalian genomes. Although the resulting sequence has gaps, the WSU team used it to flag some 10,025 genes with counterparts in the genomes of nine other mammals, including cows, horses, dogs, humans and elephants. They found 228 gene sequences that had changed significantly relative to other mammals. About 10% of those relate to the nervous system — a probable driver of the dolphin’s mental prowess.
“It was something we were hoping to find, since studies have shown that they have a large brain and high cognitive ability,” says McGowen.
One group of genes seems to be important for forming synapses in the brain, and another relates to the bizarre way dolphins sleep with one eye open and half the brain ‘turned off’. Another set corresponds to genes that in humans are related to certain brain disorders, including Alzheimer’s disease and schizophrenia. “These are interesting because any sort of gene that will affect intellectual abilities in humans signals that they may be important in cognitive functions in general,” says McGowen.
Other differences were seen in genes that relate to mitochondria, lung development, cardiovascular adaptations, lipid metabolism and milk production. The team also found a gene related to keratin production that is important for hair growth. Dolphins have only small hairs as babies, but McGowan speculates that the hair gene might be a “pseudogene” — one that remains in the genome even after losing its original function.
One similarity dolphins share with humans and elephants is a decline in the rate of change exhibited by their DNA sequences over time. The team suggests that this relates to characteristics such as body size, longevity and generation time — the time it takes for offspring to mature — and may indicate an underlying similarity in the evolutionary pressures that shaped the otherwise widely distinct species.
Photo credit: NASA