![]() Nozaki and his colleagues are interested in Pleodorina starrii because it and its close evolutionary cousins use different sex systems, so they are useful models to study the genetics of how sex evolved. More recently evolved species usually have dramatic differences between the sex cells, like the large egg and small spermatozoa of humans. ![]() "It seems very uncommon to find a species with three sexes, but in natural conditions, I think it may not be so rare," said Nozaki, the last author of the research paper published in Evolution.Įvoluntionarily ancient living things have sex cells that are similar in appearance and known as plus or minus, rather than male or female. These algae are 32- or 64-celled organisms and have small mobile (male) and large immobile (female) sex cells. The threes sexes of the Pleodorina starrii algae are male, female, and a third sex that researchers call bisexual in reference to the fact that it can produce both male and female sex cells in a single genotype and exists due to normal expression of the species' genes. Many plants and some invertebrate species have three sexes due to normal gene expression, but this is the first time a species of algae or fungi has been identified with three sexes. ![]() In species that normally have two sexes, a hermaphroditic individual who can produce both the male and female sex cells usually exists due to unusual gene expression. ![]() This phenomenon of three sexes is slightly different from hermaphroditism. ![]()
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