(ORDO NEWS) — It turned out that the ratio of males and females affects the sex roles of animals in a population.
As a rule, the more numerous sex competes more actively for a breeding partner, and the smaller sex devotes more time to raising offspring.
Moreover, the more pronounced the numerical inequality of the sexes, the more obvious their roles will be.
German scientists have shown that the ratio of adult females and males in a population determines how pronounced sex roles are in it, that is, how picky animals are when choosing a partner, how fiercely they compete for the possibility of reproduction, and how much time they devote to raising offspring.
In dioecious species, females and males often differ greatly in body structure, physiology, and behavior. These sex differences also imply differences between the sexes in the degree of rivalry, careful choice of partner, and parental care.
As a rule, females are more selective in choosing a male and pay more attention to raising offspring, and males compete more strongly with each other for the opportunity to reproduce.
However, in many species the opposite situation occurs. Now scientists have found that the ratio of adult males to females in the population is the main factor in the severity of sex roles.
Generally, the sex ratio in a population is expected to be the same. In fact, it varies considerably among different groups of animals.
For example, in isopod crustaceans, the proportion of males is only 1%, while in some bird species it reaches 90%.
In social species, the ratio of males and females can vary significantly even within the same population, between neighboring groups, in which it can change significantly over time.
As it turned out, the sex ratio strongly affects the roles. The more frequent sex will compete more strongly for partners, while the smaller one will only have to choose the most suitable applicant and pay more attention to offspring.
The more uneven this distribution, the more pronounced will be the sex roles. So, for example, in the populations of the cuckoo Centropus grillii , there are much more males, so it is the females who compete for the males, who then take care of the chicks.
Differences in the number of females and males may also be important for the survival of the species. Since in many animals, sex is determined not by genes, but by environmental factors, such as temperature.
In these species, the effects of climate change could lead to extreme sex ratios and endanger populations.
For example, the excess of males in Lacerta vivipara lizards associated with climate warming led to an increase in intraspecific aggression of females, which negatively affected their survival and fertility, and subsequently reduced the number of populations.
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