DATE2026.03.27 #Press Releases

When Nurture Turns into Birth: The Path of Evolution via Plasticity as Seen from the Medaka

Disclaimer: machine translated by DeepL which may contain errors.

-New Insights into the Adaptive Mechanisms of Organisms under Climate Change

Summary

　Why do giraffes have long necks? Lamarck, a 19th-century naturalist, suggested that the giraffe's long neck was the result of the giraffe's continual extension of its neck to feed on the leaves of tall trees, a trait that was passed down to its offspring. This "inheritance of acquired traits" is still a strong attraction today, but it is now denied. However, organisms have the ability to change their appearance and shape depending on the environment in which they were raised (phenotypic plasticity (*1)). Recently, a group of people have been found to be born with this acquired change in their upbringing, and a case has been reported that hints at the "inheritance of acquired traits" advocated by Lamarck. The molecular mechanism by which this process occurs has long been a mystery.

　In this study, we have answered this mystery at the molecular level for the first time, using the length of the medaka gut as a model.

　Associate Professor Keishi Katsumura of the Graduate School of Engineering, Kyushu University, Professor Hiroki Ota of the Graduate School of Science, The University of Tokyo, and Professor Motoyuki Ogawa of the Department of Anatomy, Kitasato University Faculty of Medicine and their colleagues analyzed seasonal and geographic variation in gut length using wild killifish from Kagawa Prefecture and other killifish strains originating from various regions in Japan. The results showed that while the length of the gut in the ancestral population (*2) changes according to the environment in which it was raised, the derived population (*3) is born with an "extremely long gut" that exceeds the range of such variation.

　The process of this transformation from "nurture" to "birth" was investigated at the molecular level, and two steps were revealed. First, seasonal changes in gut length (plasticity) correlated with seasonal changes in DNA methylation (*5) in the upstream region of Plxnb3 (*4), and deletion of this region resulted in loss of gut plasticity. Next, in the northern Japanese medaka, NJPN1, in which this plasticity was spontaneously lost, the genetic mutation originally present near Ppp3r1 (*6) was selected for and fixed an extremely long gut. Molecular evolutionary analysis suggested that the mutation in Ppp3r1 spread after the CpG site (*7) in the upstream region of Plxnb3 was reduced and plasticity was lost.

　An important point shown in this study is that this Lamarckian phenomenon, which at first glance appears as if the intestine lengthened by the environment was passed on directly to the offspring, can also be explained within the framework of Darwin's natural selection and Kimura Shisou's neutral evolution (*8). The epigenetic mechanism that had enabled flexible changes in response to the environment was lost, and then the advantageous ones were selected from the genetic variation that originally existed in the population. This is the mechanism of plasticity-driven evolution (hereafter referred to as PLE, *9) that this study demonstrates. This discovery bridges epigenetics and evolutionary biology, and also provides a new perspective for understanding the adaptive evolution of organisms under climate change.

　The research results were published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) on March 26, 2026 (3:00 AM EDT).

Figure: Mechanisms of PLE revealed in this study

Related Links

Kyushu University, Kitasato University

Published Journals