If they find a mutation in about 50% of the offspring’s DNA, they conclude that it is likely a germline mutation—a mutation inherited through the mother’s egg or the father’s sperm. Natural selection can act directly on such a mutation. Less frequent mutations are considered to occur spontaneously in tissues outside the germline; they have less to do with evolution because they won’t be passed down.
(Surprisingly often, family triad mismatches told researchers that the fathers listed in the zoo were not related to the young. Zoo representatives often shrugged. at the news and said there could be two males in the cage. The other one is the winner,” joked Bergeron.)
In the end, the researchers had 151 usable triplets, representing physically, metabolically and behaviorally diverse species such as giant killer whales, small Siamese fighting fish, and geckos strip of Texas and people. They then compared the species’ mutation rates with what we know about their behaviors and traits known as life histories. They also looked at a statistical measure for each species called effective population size, which roughly corresponds to the number of individuals needed to represent genetic diversity. (For example, even though the human population today is 8 billion, scientists often estimate our effective population size to be about 10,000 or less.) Bergeron and her colleagues. She looked for patterns of association in the numbers.
The most surprising finding that emerged from the data was a wide range of germline mutation rates. When the researchers measured how often the mutations occurred within each generation, the species changed only about 40-fold, which Bergeron said appears to be quite small compared to the differences in body size, lifespan, and age. other characteristics. But when they looked at mutation rates per year rather than per generation, the range increased to about 120 times, larger than previous studies had suggested.
The source of the difference
The study authors found that the higher the average effective population size of a species, the lower the mutation rate for that species. That provides good evidence for “Drift barrier hypothesis,” which Lynch devised more than a decade ago. “Selection is constantly trying to reduce mutation rates because most mutations are harmful,” explains Lynch. But in species with smaller effective population sizes, natural selection becomes weaker because genetic drift – the effect of pure chance on the propagation of a mutation – becomes stronger. than. That allows the mutation rate to increase.
These findings also support another idea in the scientific literature, the male-driven theory of evolution, suggesting that males may contribute more mutations to the evolution of some species than females. Bergeron and her colleagues found that germline mutation rates tend to be higher in males than females, at least in mammals and birds, although not in reptiles and fish.
The authors note one possible reason for those differences: Because males in all species copy their DNA continuously to make sperm, they face a multitude of opportunities for mutations. happen. Females and reptiles also produce eggs throughout their lives, so they are at similar risk of making genetic errors. But female mammals and birds are basically born with all of the egg cells they will produce, so their germ line is more protected.
