Research students working with Associate Professor Hisayoshi Nozaki collect algae samples in 2013 from the water Lake Sagami on Sagami River, about one hour west of Tokyo. The sperm packets swim until they hit a female colony, then split up into individual sperm cells that enter individual female cells and combine to produce a new generation.
Male colonies are recognizable by the clear packets of sperm they release into the water. starrii cells grow in spherical colonies with other individuals of their sex. In the lab, researchers can watch green P. starrii had been identified decades prior, but had not been studied in detail. 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 three 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. Through new analysis of samples collected in 20 from dam lakes along the river, Lake Sagami and Lake Tsukui, researchers identified a species of freshwater algae that evolved three different sexes, all of which can breed in pairs with each other. © Hisayoshi Nozaki, CC BY 4.0įor 30 years, University of Tokyo Associate Professor Hisayoshi Nozaki has traveled an hour west of Tokyo to visit the Sagami River and collect algal samples to understand how living things evolved different sexes. Pleodorina algae float in a water sample under a light microscope.
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