After a harsh winter in Niigata, the spring flowers burst into bloom all at once, as if busily celebrating the season. Walking my dog toward the beach, admiring the flowers that appear here and there, is a special pleasure unique to this season. In the pine grove that stretches just before the shoreline, towering black locust trees bloom simultaneously with white flowers, adding color to the long?awaited Niigata blue sky. In contrast to this beautiful scene, nearby notices about pesticide spraying and the word “pest control” catch the eye. We humans are not the only ones who have been eagerly awaiting spring; unseen creatures are also beginning to awaken.

Pine trees symbolize this region, but forests of almost entirely of Japanese black pine are vulnerable to pests. The so?called “pine wilt” spreads in an instant, and the forest quickly transforms into a graveyard of dead trees. The culprit behind this devastation is a tiny animal called a nematode. These small animals destroy the resin cells of the pine, killing the tree and promoting fungal growth, which they then use as food. The reason the damage can spread across an entire forest is their astonishing reproductive capacity. In the span of five days, one egg can produce hundreds more, and in two weeks one nematode can become hundreds of thousands. They also disperse through forests by hitching rides on insects such as the pine sawyer beetle. Never underestimate these microscopic animals; with their abilities, they can inflict staggering damage.

The pinewood nematode, which causes the pine wilt, is only one species among countless nematodes. Nematodes, also called roundworms, are thought to include more than a million species on Earth. Reflecting that diversity, species adapted to virtually every environment exist, and they are believed to play important roles as parts of ecosystems. Yet it is only in recent years that their diversity has begun to receive serious attention. Meanwhile, C. elegans is a well?known model organism; its cells are easy to observe, it is simple to culture, has a short generation time, and can be manipulated genetically in many ways, it has been used in numerous cutting?edge studies, including Nobel Prize–winning research. Thus, while nematodes are enormously diverse, there is also a solid experimental foundation for probing their underlying principles.

I aim to clarify the principles of genome evolution in living organisms by leveraging the diversity of nematodes. In particular, I focus on nematodes of the genus Pristionchus. These free?living nematodes have been the subject of vigorous field collection by the Sommer laboratory at the Max Planck Institute in Germany, and more than fifty new species have been described over the past twenty years. Nine years ago, I began studying speciation in nematodes from scratch in the Sommer lab. How a single species can diversify into multiple species through genomic change is a question that remains a major challenge in evolutionary biology. Through comparative genome analyses and quantitative trait locus mapping of these nematodes, I have shown that chromosomal fusions and fissions are important forms of genome evolution that can promote speciation. I am now testing whether inducing similar genomic changes artificially in these nematodes can experimentally reproduce speciation. In another project at Niigata University’s Brain Research Institute, we have discovered unusual genomic factors in these nematodes that may lead to insights into gene regulatory mechanisms related to brain disorders.

From this tiny animal as a starting point, a vast world of research is now beginning to unfold.

Pristionchus paicificus, a species of nematode in the genus Pristionchus. Hermaphroditic. Using differential interference contrast (DIC) microscopy, all cells can be observed alive. The head is on the right. An egg is visible in the mid?body.

Reference

1. Okumura et?al., “Life Phenomena Revealed by Various Nematodes,” Mushi no Tsudoi website. https://plaza.umin.ac.jp/wormjp/wordpress/about/about-6/
2. Yoshida et al., “Chromosome fusions repatterned recombination rate and facilitated reproductive isolation during Pristionchus nematode speciation”, Nature Ecology & Evolution, 7, 424-439 (2023)

*Article content and profile information are current as of May 2025.

Related Links

• Evolutionary Brain Pathology Lab (Yoshida Lab), Brain Research Institute, Niigata University Website

Tags (Keywords)

• #GenomeEvolution
• #Nematodes
• #PineWilt
• #PristionchusNematodes