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Scientists reveal fascinating connections between mice and a plant that blooms once in a hundred years

Their findings highlight the importance of understanding the needs of both plants and animals to ensure the health of local ecosystems. They also overturn a previously held belief about how mice store seeds

Japanese researchers from Nagoya University have revealed new aspects of the interaction between mast plants or mass seeding plants, i.e. plants that spread their seeds at once like Sasa bamboo and field mice. Their research reveals that mouse behavior (which varies between species, and varies according to environmental conditions and seasons) plays a crucial role in seed dispersal and ecosystem health in forests, and challenges existing theories about seed storage and consumption. Credit: Reiko Matsushita
Japanese researchers from Nagoya University have revealed new aspects of the interaction between mast plants or mass seeding plants, i.e. plants that spread their seeds at once like Sasa bamboo and field mice. Their research reveals that mouse behavior (which varies between species, and varies according to environmental conditions and seasons) plays a crucial role in seed dispersal and ecosystem health in forests, and challenges existing theories about seed storage and consumption. Credit: Reiko Matsushita

Hanami Suzuki and Professor Hisashi Kajimura, researchers from Univ Nagoya In Japan, new insights have been revealed about the relationship between massive seed plants and the animals that consume their seeds. Their research focused on the behavior of field mice interacting with the seeds of Sasa bamboo, which blooms once a century in central Japan.

Diverse factors affecting seed utilization by mice

The researchers found that the patterns of use that field mice make of seeds is different between species (large Japanese field mouse Apodemus speciosus and small Japanese field mouse A. argenteus), and also depends on the presence or absence of underground vegetation, forest tree species (broad-leaved forest or coniferous forest) and season (summer or fall).

Their findings highlight the importance of understanding the needs of both plants and animals to ensure the health of local ecosystems. They also overturn a previously held belief about how mice store seeds.

Sting behavior in dwarf bamboo

An example of a behavior called 'disposal and storage' - mice carrying seeds from a container and burying them in the ground. Credit: Hanami Suzuki, Hisashi Kajimura

Plants of the dwarf bamboo species (Sasa borealis) exhibit masting behavior in large areas. Mustering behavior means that plants of certain species time their flowering and seed production together with many individuals in a population at regular intervals to increase pollination rates as well as to deal with animals that feed on the seeds.

Masting events are rare, but can also occur at intervals of up to 120 years. But when they do occur, the abundance of seeds created in the forest provides readily available food for various animals, especially rodents such as field mice.

Observations on the behavior of field mice

To better understand the behavior of voles during mating events, the researchers placed seeds in shallow mesh baskets to simulate mass flowering and seed formation. Next, they used an automated camera to record the foraging behavior of field mice in different forest environments and seasons.

At first, as expected, some of the mice ate seeds they found there. However, others would perform "dispersal behavior", carrying seeds away and storing them for later eating. This is an example of a behavior called 'removal and caching'.

Species-specific behaviors and environmental influence

The two species of voles behaved differently. The large Japanese field mouse ate the seeds in places where plants and bushes protected them from mouse predators. It also carried the seeds from areas where they were more vulnerable, such as areas without vegetation, to more protected areas.

The small Japanese field mouse, on the other hand, was more likely to carry seeds elsewhere even when protective vegetation was present. The researchers suspect that the differences in mouse body size probably explain this behavior. In short, larger mice worry less about other rodents stealing their food. But they worry more that they will be devoured.

Impact on seed dispersal and ecosystem health

Seasonality and tree species also appeared to affect how often the mice ate the seeds. The rodents were more likely to eat seeds in the summer than in the fall, probably due to food availability.

They were also more likely to consume seeds in coniferous forests than in broadleaf forests, again probably due to the availability of other food sources. Since alternative foods for later consumption, especially acorns, are more common in broadleaf forests, a mouse can afford to consume the seeds.

Mice were more likely to eat their food immediately in broadleaf forests during autumn. This behavior plays an important role in ensuring seed distribution throughout the forest. According to Suzuki: "Forest-dwelling voles play an important role in the distribution and regeneration of trees because they act as seed dispersers that carry and store seeds. This suggests that we should re-evaluate the relationship between the simultaneous seeding of S. borealis and field mice. It may also spread to choosing food with other tree seeds and predicting the regeneration of the forest and the sequence of vegetation associated with it."

Challenging accepted theories

Suzuki explained that the mass seed production of Sasa bamboo species is known worldwide to cause large outbreaks of field mice, which are typical seed eaters. It has been studied as a prominent example of the effects of plants on animals. As seed predators, the choices and behavior of mice, such as feeding or "removal and cache", can lead to the inhibition of certain plants or enhance their ability to regenerate. When I learned about this, I became very interested in field mice as an important species for the future of forest ecosystems."

"Many studies have been done on the relationship between field mice and seeds," she continued. "Established theory states that larger seeds, such as chestnuts and acorns, are subject to removal and burial, while smaller seeds are consumed more quickly. However, our results revealed that even much smaller seeds, such as those of Sasa borealils, which weigh only 0.025 g per seed, are also a burrowing target for mice. Therefore, the dispersal and storage behavior of small seeds by field mice indicates that the accepted theory must be changed."

"Our experiments showed that field mice consider the environment and use Sasa bamboo seeds in a flexible way," concludes Kajimura. "Since this type of behavior affects tree regeneration, as well as underground vegetation, our findings show the effect of mice on creating complexities in the forest ecosystem."

Reference: “Utilization of Sasa borealis seeds by the Japanese field mouse: discovery of a small seed cache” by Hanami Suzuki and Hisashi Kajimura, 10 Aug 2023, Frontiers in Ecology and Evolution.
DOI: 10.3389/fevo.2023.1124393

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