While the sex of most animals is determined by genes, eels take a different approach by 'voting' on their sex through environmental factors. This special mechanism demonstrates the marvellous wisdom of the evolution of life.
The sex of eels is closely related to population density. When the environment is crowded and competition is fierce, eels tend to develop into males. Taking European eels as an example, eels are often crowded in artificial breeding ponds due to limited space. Research data shows that the male ratio of European eels is as high as 90% in such an environment. In small tanks, eels are like living in a 'densely populated' city. In order to adapt to the fierce competition, a large number of individuals choose to become males in order to reduce the consumption of resources caused by reproduction, and use more energy for survival.
Have you ever thought that water temperature also affects the sex of eels? The higher water temperature in the tropics significantly increases the proportion of male eels, while the salinity of the habitat also affects the sex of eels. Estuaries are in the transition zone between seawater and freshwater, and the special salinity environment makes eels here more prone to feminisation, which is presumed to be related to the effect of salinity on osmolality regulation and the expression of sex-related genes.
Female eels require large amounts of energy for ovarian development and spawning, so when resources are sufficient, 'investing' in females can improve reproductive efficiency; when resources are scarce and competition is fierce, increasing the proportion of males can reduce the consumption of resources for reproduction and ensure the survival of individuals.
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