The findings of a new study has suggested that a few males are enough to fertilise all the females and thus the number of males, therefore, has little bearing on a population’s growth. However, they are important for purging bad mutations from the population.
The findings are from a study done by Uppsala University in the United States, which provides thorough knowledge of the possible long-term genetic consequences of sexual selection. The results are published in the scientific journal Evolution Letters, reports news agency PTI.
The study supported the theory that in many animals’ species selection acting on males can impose the unpredictable benefit to the population of causing offspring to inherit healthy genes.
Tough competition among males results in selective elimination of individuals with many harmful mutations, preventing them from passing on said mutations. This may exert positive long-term effects on a sexually reproducing population’s growth and persistence, the study noted.
“When deleterious mutations are purged from a population through rigorous selection in males, resulting in fewer males reproducing, the process can take place with little or no effect on population growth. This is because relatively few males suffice to fertilise all the females in a population, hence, whether those females are fertilised by few males or many males makes little or no difference to the number of offspring those females can produce, especially in species where the male doesn’t look after its own offspring,” said Karl Grieshop, an evolutionary biologist at Canada’s University of Toronto and the study’s lead author.
In contrast, such rigorous selection in females would result in fewer females reproducing, hence fewer offspring produced, which could lead to a massive population decline or even extinction, Grieshop noted.
The researchers of the university used 16 genetic strains of seed beetle (Callosobruchus maculatus) to investigate how the inferred number of harmful mutations in each affected the reproductive ability (fitness) of females and males. With intensive inbreeding of strains followed by crosses among them, it became possible to quantify the cumulative effects of each strain’s unique set of mutations.
By comparing the inbred strains to the crosses among them, the researchers were able to see that these mutations harmed both females and males nearly equally. However, when looking only at the crosses among strains, these mutational effects were only manifest in male fitness. In the females, the harmful effects of the mutations they carried were not detectable in this more genetically variable background and would therefore not be purged effectively via female-specific selection in nature, the study stated.
“This indicates that although these mutations do have a detrimental effect on females’ reproduction, they are more effectively removed from the population by selection acting on male carriers than female carriers. Previous research from our group and others has succeeded in showing this effect by artificially inducing mutations, but this is the first direct evidence that it ensues for naturally occurring variants of genes,” Grieshop said.
