According to scientists, Pleodorina starrii is an algae with female, male, and ‘bisexual’ characteristics.

A species of freshwater algae collected from Japanese lakes has done something unusual: it has evolved to have three distinct sexes, all of which breed in pairs. The three sexes are male, female, and bisexual, which the researchers attribute to the third sex’s ability to produce both male and female sex cells in a single genotype.

It is not a hermaphrodite organism because its sexual cells developed under normal genetic expression, whereas a hermaphrodite individual who can produce both male and female sex cells exists due to an unusual genetic expression.

The discovery is the result of 30 years of research by Hisayoshi Nozaki, an associate professor at the University of Tokyo. During this time, he has traveled to the Sagami River, where he has collected samples from the river and nearby artificial lakes.

Sexual peculiarity

Algae are a large and diverse group of eukaryotic creatures that obtain energy through photosynthesis. Pleodorina starrii, the algae that has proven to be so unique, was previously thought to have two sexes that mated with each other, a mating system known as heterothalic. Researchers discovered evidence that P. starrii can be male, female, or of a third sex.

“Isolated colonies of one sex can be mixed with isolated colonies of the opposite sex, and the sex ratio of their offspring can be useful clues for researchers to understand the genetics of sex determination,” the authors write.

Male colonies can be identified by the clear packs of sperm they release into the water. Sperm packs swim to a female colony, where they divide into individual sperm cells, which are then introduced into individual female cells and combined to produce a new generation. And the ‘bisexual factor’ gene is found on a different chromosome than the male and female sex cells.

Given the small size of these organisms (32 or 64 cells), this is a fantastic discovery. It had never been discovered that a species of algae or fungi had three sexes before. The team refers to it as a “new haploid mating system” that is unique to algae.

Depending on the stage of the life cycle in which they are found, algae can reproduce asexually (by cloning themselves) or sexually (with a partner). It can be haploid (only one set of chromosomes) or diploid (two sets of chromosomes) (with two sets).

However, researchers discovered that P. starrii, which is genetically bisexual, produces male and female sexual colonies when isolated and is reproduced through cloning. When they looked closer, they discovered that the bisexual factor gene could be passed down to the next generation, distinguishing it from a single mutation.

Although algae are very different from humans, scientists believe they can help us understand how different sexual systems, such as male and female, evolved.




Gerardo Franco is a science communicator, with studies at the Georgia Institute of Technology.

Love podcasts or audiobooks? Learn on the go with our new app.

Recommended from Medium

Can we Bring Back the Dodo?

Making Sense of Science with David Robert Grimes

Global Attitudes Towards GM Crops Are More Diverse Than You’d Expect — For Surprising Reasons

To Infinity and Beyond

Engineering virus nanoparticles to modulate coagulation

Stories on Exploring with Harmit Malik

APEC 2/13: Antigravity, Inertial Propulsion & Exotic Materials

Exciting Paleontological Discoveries You Probably Missed in September

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Gerardo Franco

Gerardo Franco

Gerardo Franco is a science communicator, with studies at the Georgia Institute of Technology.

More from Medium

Living in Singapore, then and now

Lindy Effect in Wireless Communications

Why Treating Disease Starts in the Gut

How Plants And Herbs Were First Identified For Medicinal Use