[An article from this laboratory]
If mates are selected based on the gender characteristics shared between males and females, then the choice of mates between males and females may be the same ( mutualmate choice ). But to what extent does this common choice drive phenotypic changes? If both males and females tend to choose the same phenotypic characteristics when choosing a mate (for example, regardless of men and women, they like to find a high IQ as a mate), then how will this choice affect the evolution of the phenotype? Do males and females respond the same to selection? In this study, artificial selection was used to study the phenotype of epidermal hydrocarbons ( CHCs ) of Drosophilaserrata in the face of co-selection from male and female. After 10 generations of manual selection, the phenotype of CHCs has changed significantly in both sexes, but the adaptive results related to it have shown great differences in both sexes. Changes in males led to an increase in the success rate of male courtship at the genetic level; although phenotypic changes also appeared in females, it had no effect on the success rate of female courtship . This shows that the sexual selection of males to females may be more related to the environment rather than genetics. Therefore, compared with female selection of males , male selection of females may not have much effect on the evolution of this species .
Sex selection caused by courtship has always been regarded as an important factor in phenotypic diversity. However, many current researches on sexual selection have focused on the sexual selection of males by females. So to what extent does the male's choice of females affect the population's phenotypic diversity? In some species, some phenotypic characteristics will become common selection targets for both sexes. This common choice will enhance or inhibit the performance of the phenotype in the population.
The key to understanding this sexual selection is to find out the genetic relationships behind the related traits. Previous studies have shown how female sexual selection can improve females’ adaptability. For example, females will choose males who are more able to take care of their offspring as mating objects, or males with some excellent traits. Through this choice, females Can improve the quality of offspring. Compared with females, males pay much less on their offspring, so males may choose females more directly, choosing only those females with high fertility as mating objects. Therefore, it is precisely because of this difference in mate selection strategies between males and females that even if a phenotype is the common selection target of both males and females, the way they choose and the meaning they represent may be different.
Using traditional quantitative genetics methods to study the relationship between phenotype, genotype, and fitness can help us understand the differences in female and male selection. But the measurement of fitness is a very difficult problem. Through manual selection and subsequent removal of phenotypic changes after this selection, fitness can be well measured. This study is to study the relationship between the neutral selectivity, courtship success rate and fitness of Drosophila through multiple generations of artificial selection. CHCs are a kind of pheromone in Drosophila, composed of multiple components, and play an important role in Drosophila courtship. The selection pressure and direction of CHCs are very different between male and female fruit flies . The greatest selective pressure is applied to CHCs through artificial behavior to verify the evolutionary process of sexual attraction related to CHCs .
result
Sexual antagonism selection
By CHCs study of phenotype and mating success is confirmed, the driving force between the sexes courtship choice indeed phenotypic evolution. However, the choice of CHCs differs between the sexes, and the choice of males is stronger than the choice of females. There are differences in the direction of choice. Some CHCs are liked by females but disgusted by males (for example, 5,9-C25:2 ). On the contrary, some are liked by males and disgusted by females (for example, 5,9-C29:2 ). This shows that although CHCs are simultaneously selected by both sexes, they are subject to different selection pressures and the direction of selection is not necessarily the same.
By manual selection of male, 10 after generations, the male population associated CHCs deviates significantly from the original value and exhibits an increasing trend; associated with the female CHCs or associated with both genders CHCs deviate from the original value, but exhibits reduced tendency. By selection of the artificial female, 10 after generations, population-related females CHCs or associated with both genders CHCs increased, while associated with male CHCs reduced.
A: In males, selective pressure on males (ML1, ML2) promoted the evolution of related traits, while selective pressure on females (FL1, FL2) and both sexes (MS1, MS2) did not promote male traits Evolution; B: In females, the simultaneous selection pressure on females (FL1, FL2) and both sexes (MS1, MS2) promoted the evolution of female traits, while selective pressure on males failed to promote females Changes in related traits.
Will the manual selection of CHCs change the courtship success rate? This study found that the artificial selection of males significantly increased the courtship success rate of males; while the artificial selection of females did not find any influence on the courtship success rate of females .
Manual selection of one phenotype usually comes at the expense of other phenotypes. Will artificial selection of CHCs affect other phenotypes? In this study, after 10 generations of artificial selection, artificial selection was removed, and it was found that the phenotype of CHCs had returned to the previous state, which means that whether it is male or female, the artificial selection of CHCs phenotype weakened some others Phenotype adaptability, there is antagonistic behavior between CHCs and these phenotypes.
In addition, this study continued to understand the genetic basis of the differences between the sexes, and found that the changes in male CHCs mainly come from low-frequency alleles, while the changes in female CHCs are mainly due to the middle-frequency alleles playing a greater role. This also means that female individuals can adapt faster when faced with selection pressure, while male individuals are slower to adapt to selection pressure . This means that the change trend of FL in Figure 1 is more sensitive than that of ML .
to sum up
Although some traits in serrata fruit flies are jointly selected by both sexes, the genetic mechanisms behind them are different. For males, the change of phenotype significantly improves the courtship success rate of male individuals. Once the selection pressure is removed, the phenotype quickly returns to its previous state due to the antagonism of other phenotypic adaptations. For females, phenotypic changes did not increase the courtship success rate, which means that in females, the evolution of CHCs may not be subject to male selection pressure. For males, the phenotype of CHCs may reflect the information of their genome and the quality of their genes. For this reason, females’ selective pressure on males can bring benefits to the offspring of females. This study also explains to some extent why female secondary sexual characteristics are not as common as male secondary sexual characteristics.
=== An easy-to-understand improper explanation ===
Among the men and women who successfully found the target, it was found that their overall level of EQ was higher than that of single men and women. On the surface, both men and women like to look for people with high emotional intelligence, but in reality they are not necessarily. Men looking for high EQ does not mean that men really like women with high EQ. It may also be that certain genes that cause high EQ will make women more beautiful, so what men really like are women with beautiful appearance; while women look for A man with a high EQ is because he has a high EQ and knows how to care for his children and take care of his family. Therefore, for the entire population, the increase in group EQ is mainly due to women's choice of men, and this choice has a genetic basis.
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文献来源：Gosden, T. P., Reddiex, A. J., & Chenoweth, S. F. (2018). Artificial selection reveals sex differences in the genetic basis of sexual attractiveness. Proceedings of the National Academy of Sciences, 115(21), 5498-5503.
