Researchers from the University of Tokyo and several other Japanese universities have discovered a type of green algae known as Pleodorina starii with three distinct sexes – male, female, and a third sex collectively referred to as “hermaphrodite.”
Biologist Hisayoshi Nozaki, one of the researchers, stated: “Species with three sexes are quite rare, but in the natural environment, this is not as uncommon as we might think.”
The reproduction of algae also has many diverse variations.
Algae is a general term for a group of eukaryotic organisms capable of photosynthesis. They are not plants, as they lack many fundamental characteristics. They are also not bacteria, nor are they fungi.
Algae include multicellular species such as giant kelp and unicellular species like small flagellates. The reproduction of algae also exhibits many diverse variations. They can reproduce asexually (self-replicating) or with a mate, depending on the stage in their life cycle – at times they have a single set of chromosomes (haploid), and at other times, two sets (diploid).
Additionally, there are hermaphroditic algae that can change sex based on the genetic expression of the individual. However, the green algae P. starii exhibit a hermaphroditic form that contains both male and female reproductive organs. They display a completely new haploid mating method that is particularly unique for algae.
P. starii forms colonies containing 32 or 64 cells of the same sex, either male or female. Male cells transmit genetic information to female cell colonies to initiate the reproductive process.
The hermaphroditic form of P. starii can form hermaphroditic colonies and thus can mate with other male, female, or hermaphroditic colonies.
Male colony (left). Male colony with a bundle of chromosomes (middle). Male colony and gametes (right).
Researchers are intrigued by this discovery as it may provide new insights into the evolutionary processes of sexual characteristics.
“Mixed mating systems represent intermediate states in the evolution from dioecy (male-female) to monoecy (only hermaphroditic) in diploid organisms,” the research team stated in their report.
“However, the haploid mating method with three sexes in one species has not been reported before.”
For over 30 years, Nozaki has continuously collected algae samples from the Sagami River on the outskirts of Tokyo. The team utilized samples taken from lakes scattered along the river’s length in 2007 and 2013.
The team also discovered that this hermaphroditic algae possesses a genetic factor for hermaphroditism, distinct from the male and female genes previously identified. Hermaphroditic cells contain male genes but can produce offspring that are either male or female.
The study concludes: “The existence of three sexes within a species may not be a rare phenomenon in nature. Studies on the collected specimens may reveal this characteristic in many other algae species in the future.”
The research was published in the journal Evolution.
