Similar to other unicellular organisms, Paramecium aurelia typically reproduce asexually via binary fission or sexually via cross-fertilization.
However, studies have shown that when put under nutritional stress, Paramecium aurelia will undergo meiosis and subsequent fusion of gametic-like nuclei.
[citation needed] In Paramecium tetraurelia, vitality declines over the course of successive asexual cell divisions by binary fission.
[citation needed] Similar to Paramecium aurelia, the parasitic ciliate Tetrahymena rostrata has also been shown to engage in meiosis, autogamy and development of new macronuclei when placed under nutritional stress.
[8] It is hypothesized that this is a survival mechanism employed when the cell is in stressful environments, and thus not able to allocate all resources to creating offspring.
[13] An adaptive benefit of meiosis that may explain its long-term maintenance in self-pollinating plants is efficient recombinational repair of DNA damage.
First, if there is an unfavorable change in the environment that puts the ability to deliver offspring at risk, then it is advantageous for an organism to have autogamy at its disposal.
In other organisms, it is seen that genetic diversity arising from sexual reproduction is maintained by changes in the environment that favor certain genotypes over others.
Aside from extreme circumstances, it is possible that this form of reproduction gives rise to a genotype in the offspring that will increase fitness in the environment.
[19] It is possible that the nutrition deprived state of the parent cells before autogamy created a barrier for producing offspring that could thrive in those same stressful environments.
[citation needed] In flowering plants, autogamy has the disadvantage of producing low genetic diversity in the species that use it as the predominant mode of reproduction.
[21] In plants, selfing can occur as autogamous or geitonogamous pollinations and can have varying fitness affects that show up as autogamy depression.
After several generations, inbreeding depression is likely to purge the deleterious alleles from the population because the individuals carrying them have mostly died or failed to reproduce.
[citation needed] If no other effects interfere, the proportion of heterozygous loci is halved in each successive generation, as shown in the following table.
However, due to the little overall genetic variation that arises in progeny, it is not fully understood how autogamy has been maintained in the tree of life.