Sex as a formality: Males are unnecessary in stick insects!?

by Japanese National Institute for Basic Biology
Feb. 5, 2025

Among animals where sexual reproduction is common, there are quite a few species that reproduce only with females. In such species, females give birth to female offspring (this is called parthenogenesis). However, due to errors in the developmental process, males may be born on extremely rare occasions. Whether these males function as males is important in considering the irreversibility of parthenogenesis. However, because rare males are so rare, they have not been studied much. Many species of stick insects, familiar insects with branch-like shapes, are known to reproduce parthenogenetically. Most of the stick insects collected in the wild, including the false stick insect (also simply called stick insect), which is the most common stick insect in Japan, are female. However, it was also known that males were discovered very rarely.

This time, a group led by Assistant Professor Tomonari Nozaki (formerly a JSPS Postdoctoral Fellow) of the National Institute for Basic Biology, Professor Kenji Suetsugu of Kobe University, and Associate Professor Shingo Kaneko of Fukushima University discovered that while males that rarely appear in the parthenogenetic species Ramulus mikado are morphologically and behaviorally normal, they have completely lost their reproductive function. The rare males collected in the field have external genitalia characteristic of male stick insects and actively mated with females of the same species. However, when the genotypes of the offspring obtained as a result of mating were analyzed, no male-derived genes were detected at all. This means that the females gave birth to offspring through parthenogenesis, regardless of whether they mated with males or not.

Keep reading (in Japanese): https://www.nibb.ac.jp/press/2025/02/05.html

Read the Ecology paper: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.4522