What is sexual reproduction?
What is the cost of sexual production?
There are two different types of reproduction, asexual reproduction, where a new offspring is produced by a single parent and sexual reproduction, where an offspring is produced by two individuals. But sexual reproduction requires more energy than asexual reproduction.
The growth rate of an asexually reproducing population is twice the rate of a sexually reproducing population. This is because sexually reproducing individuals must produce both sexes, but only half of them can give birth to their own progeny. In contrast, every asexually reproducing individual can produce their own offspring. This is known as a two-fold cost of sexual reproduction.
How do scientists try to explain its efficiency?
The researchers have suggested hypotheses to address the “two-fold cost of sex”: the cost of producing a large number of male gametes and the cost of meiosis (cell division). They tested these hypotheses by computer modelling.
The first hypothesis was the ‘seesaw effect’ by which a large number of harmful mutations were eliminated. The individual having sex controlling genes and allowing meiosis to occur produced four gametes. The gametes with sex-controlling genes could combine, fixing it in the population and eliminating the cost of meiosis. Also, harmful mutations, whether associated with the sex-controlling genes, were discarded.
Image Credits: Wikimedia
The second hypothesis was the development of anisogamy via ‘inflated isogamy’, developed from the first hypothesis. The researchers stated that multicellular organisms with higher energy generation evolved. The size of gametes increased (inflated isogamy) as the survival rate of offspring increased due to increased resources in larger gametes. The male gametes’ size was reduced to fertilise more female gametes depending on the inflated female gametes to provide the survival resources. This technique did not involve any cost on the female part. It may have caused their counter-adaptation to the meiosis in females resulting in one oocyte (female gamete) per gametocyte (a germ cell that divides to form gametes).
With these hypotheses, researchers also hypothesised that the first sexual reproduction was the self-fertilising event that required only one individual. However, these two hypotheses are still in their initial phases and further research is required to discuss certain beliefs and conclusions underlying them.
The detailed study was published in the Journal of Ethology.
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