Press Releases

DATE2021.05.18 #Press Releases

Genome study reveals how green algal species became hermaphrodite


Overview of the press release

A research team has shed light on how male and female sex-determining chromosomes in the ancestor of Volvox africanus, a species of green alga, were changed after evolving into a hermaphrodite species.
Evolutionary transitions between separate sexes (dioecy) and other mating systems such as hermaphrodites (possessing both male and female sex functions) are common across animals, plants, and algae. However, the fates of male and female sex-determining chromosomes in an ancestral dioecious species after an evolutionary transition to a hermaphrodite species have remained unresolved in all organisms.
To understand what happened to the male and female sex-chromosomes after the transition, Hisayoshi Nozaki, a researcher in the Department of Biological Sciences at the Graduate School of Science, and a research team examined active culture strains of two closely related dioecious (V. reticuliferus) and hermaphrodite (V. africanus) species of Volvox that were collected from Lake Biwa, an ancient lake in Japan.

Figure:Female sexual spheroids and an asexual spheroid of Volvox reticuliferus. Photo by Hisayoshi Nozaki.


They performed de novo whole genome sequencing of male and female genotypes of the two Volvox species. Based on the comparative and evolutionary analyses of these genome data, they uncovered the evolutionary transition from dioecious to hermaphrodite species by focusing on the ancestral male and female sex-determining chromosomes. They found that the hermaphrodite species, V. africanus, retained a nearly intact female-derived sex-chromosomal region and had separate regions containing key male genes. This suggests that an ancestral female genotype had likely become hermaphrodite by acquiring male genes.
“The finding that the hermaphrodite species evolved from an ancestral female that acquired male genes suggests fundamental differences in expressing sexual characteristics between male and female sexes in organisms,” said Nozaki. “Resolving the evolutionary significance and molecular bases of such differences will be an important area of future research in the biological sciences.”

Publication details


Proceedings of the National Academy of Sciences of the United States of America (PNAS)

Three genomes in the algal genus Volvox reveal the fate of a haploid sex-determining region after a transition to homothallism
Kayoko Yamamoto, Takashi Hamaji, Hiroko Kawai-Toyooka, Ryo Matsuzaki, Fumio Takahashi, Yoshiki Nishimura, Masanobu Kawachi, Hideki Noguchi, Yohei Minakuchi, James G. Umen, Atsushi Toyoda and Hisayoshi Nozaki*