From University of Tokyo [(東京大学](JP) via Science Alert (US) : “Scientists Discover The First Known Algae Species With Three Distinct Sexes”

From University of Tokyo [(東京大学](JP)



Science Alert (US)

13 JULY 2021

Credit: Kohei Takahashi.

Although we might think of ourselves as far removed from blobby green algae, we’re not really that different.

An algae explosion a few hundred million years ago is thought to have been what allowed all human and animal life to evolve, and all told there’s only about one and a half billion years between us in terms of evolution.

Plus, according to a Japanese team of researchers, algae could actually help us to understand how different sex systems – like male and female – evolved in the first place.

Researchers from the University of Tokyo and a number of other Japanese universities have discovered that a type of green algae called Pleodorina starrii has three distinct sexes – ‘male’, ‘female’, and a third sex that the team have called ‘bisexual’. This is the first time any species of algae has been discovered with three sexes.

“It seems very uncommon to find a species with three sexes, but in natural conditions, I think it may not be so rare,” said one of the researchers, University of Tokyo[(東京大] (JP) biologist Hisayoshi Nozaki.

Algae isn’t a very specific scientific classification. It’s an informal term for a huge collection of different eukaryotic creatures that use photosynthesis to get energy. They’re not plants, as they lack many plant features; they’re not bacteria (despite cyanobacteria sometimes being called blue-green algae); and they’re not fungi.

Everything from many-celled giant kelp species, all the way down to cute single-celled dinoflagellates can be classed as algae.

Because algae are such a big, diverse group, there’s lots of variation in the way that they get it on, but generally algae are able to reproduce asexually (by cloning themselves) or sexually (with a partner), depending on the life cycle stage they’re in. This can be either haploid (with a single set of chromosomes), or diploid (with two sets).

There’s also hermaphroditic algae that can change depending on the gene expression of the organism. Having three sexes, including hermaphrodites, is called ‘trioecy’.

But the volvocine green algae P. starrii is different from this again. The bisexual form of this haploid algae has both male and female reproductive cells. The team describe it as a “new haploid mating system” completely unique to algae.

P. starrii form either 32 or 64 same-sex celled vegetative colonies and have small mobile (male) and large immobile (female) sex cells similar to humans. The male sex cells are sent out in the world in sperm packets to find a female colony to attach to.

Bisexual P. starrii have both, can form either male or female colonies, and therefore can mate with either a male, a female, or another bisexual.

Sexually induced male colony of algae (left). Female colony with male sperm packet (center). Female colony with dissociated male gametes (right). Credit: Kohei Takahashi.

The researchers are particularly excited because other closely related algae have different sex systems, meaning the discovery might be able to tell us more about how these sexual changes evolve.

“Mixed mating systems such as trioecy may represent intermediate states of evolutionary transitions between dioecious (with male and female) and monoecious (with only hermaphrodites) mating systems in diploid organisms,” the team write in their new paper.

“However, haploid mating systems with three sex phenotypes within a single biological species have not been previously reported.”

For 30 years, Nozaki had been collecting algae samples from the Sagami River outside of Tokyo. Samples that were taken from lakes along that river in 2007 and 2013 were used by the team for the new finding.

The team separated the algal colonies and induced them to reproduce sexually by depriving them of nutrients, discovering that the bisexual algae had a ‘bisexual factor’ gene that was separate to previously discovered male and female specific genes.

The bisexual cells had the male gene as well, but can produce either male or female offspring.

“Co-existence of three sex phenotypes in a single biological species may not be an unusual phenomenon in wild populations,” the researchers conclude.

“The continued field-collection studies may reveal further existence of three sex phenotypes in other volvocine species.”

The research has been published in Evolution.

See the full article here .


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The University of Tokyo [(東京大学](JP) aims to be a world-class platform for research and education, contributing to human knowledge in partnership with other leading global universities. The University of Tokyo aims to nurture global leaders with a strong sense of public responsibility and a pioneering spirit, possessing both deep specialism and broad knowledge. The University of Tokyo aims to expand the boundaries of human knowledge in partnership with society. Details about how the University is carrying out this mission can be found in the University of Tokyo Charter and the Action Plans.

The university has ten faculties, 15 graduate schools and enrolls about 30,000 students, 2,100 of whom are international students. Its five campuses are in Hongō, Komaba, Kashiwa, Shirokane and Nakano. It is among the top echelon of the select Japanese universities assigned additional funding under the MEXT’s Top Global University Project to enhance Japan’s global educational competitiveness.

University of Tokyo (Todai) is considered to be the most selective and prestigious university in Japan and is counted as one of the best universities in the world. As of 2018, University of Tokyo’s alumni, faculty members and researchers include seventeen Prime Ministers, sixteen Nobel Prize laureates, three Pritzker Prize laureates, three astronauts, and a Fields Medalist.

The university was chartered by the Meiji government in 1877 under its current name by amalgamating older government schools for medicine, various traditional scholars and modern learning. It was renamed “the Imperial University [帝國大學; Teikoku daigaku]” in 1886, and then Tokyo Imperial University [東京帝國大學; Tōkyō teikoku daigaku] in 1897 when the Imperial University system was created. In September 1923, an earthquake and the following fires destroyed about 700,000 volumes of the Imperial University Library. The books lost included the Hoshino Library [星野文庫; Hoshino bunko], a collection of about 10,000 books. The books were the former possessions of Hoshino Hisashi before becoming part of the library of the university and were mainly about Chinese philosophy and history.

In 1947 after Japan’s defeat in World War II it re-assumed its original name. With the start of the new university system in 1949, Todai swallowed up the former First Higher School (today’s Komaba campus) and the former Tokyo Higher School, which thenceforth assumed the duty of teaching first- and second-year undergraduates, while the faculties on Hongo main campus took care of third- and fourth-year students.

Although the university was founded during the Meiji period, it has earlier roots in the Astronomy Agency (天文方; 1684), Shoheizaka Study Office (昌平坂学問所; 1797), and the Western Books Translation Agency (蕃書和解御用; 1811). These institutions were government offices established by the 徳川幕府 Tokugawa shogunate (1603–1867), and played an important role in the importation and translation of books from Europe.

In the fall of 2012 and for the first time, the University of Tokyo started two undergraduate programs entirely taught in English and geared toward international students—Programs in English at Komaba (PEAK)—the International Program on Japan in East Asia and the International Program on Environmental Sciences. In 2014, the School of Science at the University of Tokyo introduced an all-English undergraduate transfer program called Global Science Course (GSC).


The University of Tokyo is considered a top research institution of Japan. It receives the largest amount of national grants for research institutions, Grants-in-Aid for Scientific Research, receiving 40% more than the University with 2nd largest grants and 90% more than the University with 3rd largest grants. This massive financial investment from the Japanese government directly affects Todai’s research outcomes. According to Thomson Reuters, Todai is the best research university in Japan. Its research excellence is especially distinctive in Physics (1st in Japan, 2nd in the world); Biology & Biochemistry (1st in Japan, 3rd in the world); Pharmacology & Toxicology (1st in Japan, 5th in the world); Materials Science (3rd in Japan, 19th in the world); Chemistry (2nd in Japan, 5th in the world); and Immunology (2nd in Japan, 20th in the world).

In another ranking, Nikkei Shimbun on 16 February 2004 surveyed about the research standards in Engineering studies based on Thomson Reuters, Grants in Aid for Scientific Research and questionnaires to heads of 93 leading Japanese Research Centers. Todai was placed 4th (research planning ability 3rd/informative ability of research outcome; 10th/ability of business-academia collaboration 3rd) in this ranking. Weekly Diamond also reported that Todai has the 3rd highest research standard in Japan in terms of research fundings per researchers in COE Program. In the same article, it is also ranked 21st in terms of the quality of education by GP funds per student.

Todai also has been recognized for its research in the social sciences and humanities. In January 2011, Repec ranked Todai’s Economics department as Japan’s best economics research university. And it is the only Japanese university within world top 100. Todai has produced 9 presidents of the Japanese Economic Association, the largest number in the association. Asahi Shimbun summarized the number of academic papers in Japanese major legal journals by university, and Todai was ranked top during 2005–2009.

Research institutes

Institute of Medical Science
Earthquake Research Institute
Institute of Advanced Studies on Asia
Institute of Social Science
Institute of Industrial Science
Historiographical Institute
Institute of Molecular and Cellular Biosciences
Institute for Cosmic Ray Research
Institute for Solid State Physics
Atmosphere and Ocean Research Institute
Research Center for Advanced Science and Technology

The University’s School of Science and the Earthquake Research Institute are both represented on the national Coordinating Committee for Earthquake Prediction.