Plant pathogens infect plants by various routes from all the environments surrounding plants, such as wind, rain, soil, and when insects contact plants to suck on them or feed. Many pathogens invade through wounds or natural openings (stomata, water pores, etc.), and actively enter the plant body. Such invasion can occur regardless of the stage of host plant growth and development. However, some pathogens take advantage of the timing of plant reproduction, such as pollination and seed formation, to invade plants. These pathogens do not immediately cause disease in the host plants, but multiply insidiously in floral organs and seeds before developing the disease. At present, with both pollen and seeds distributed internationally for commercial use, there is an increasing risk of widespread transmission of pathogens along with pollen or seeds. Of the pathogens that cause pandemics, this study is focused on phytopathogenic bacteria that infect floral organs and seeds, and I introduce the ecology of their plant infection and relationships with other indigenous bacteria.

View full abstract

Plant-microbe interactions in floral organs greatly affect host survival and reproduction through various mechanisms, including vertical transmission of microbes from flowers to seeds and the effects on pollinator attraction. The influences of microbial dispersal by pollinators on the floral microbiome have been extensively explored; however, recent meta-barcoding studies have defined new factors that modulate the microbiome. The floral organs -- pistil, stamen, and petals -- provide diverse habitats for floral microbes. Various floral characteristics, such as UV reflection by petal surfaces, affect floral microbes by changing the environment. Host-plant immunity places strong selective pressure on microbes. The interactions between host plants and various organisms, including pollinators and nectar robbers, affect the floral microbiome by facilitating microbial dispersal and triggering inducible defensive responses of the host plant. The plant environment and other plants growing near the host plant affect microbial migration to host flowers through mechanisms mediated by wind, rain, and flower visitors, which may result in the context-dependency of the floral microbiome. Complex interactions among such factors may determine the flower microbiome. However, there remains a lack of clarity concerning how such factors influence the microbiome, as well as the effects of such microbial changes on host-plant growth and fitness. Experimental studies are needed to elucidate fully plant-microbe interactions on flowers.

View full abstract

Studies of the relationship between floral microbes and flower-visiting animals (hereafter, flower visitors) have increased rapidly since 2000, driven in part by the increasing availability of metagenomic analyses. This review presents the history and latest findings in this field, classifying the studies into three categories: (1) the role of flower visitors in the formation of floral microbiomes, (2) the impact of floral microbes on the behaviour and health of flower visitors, and (3) the impact of floral microbes carried by flower visitors on the health and reproductive success of plants. The mutual relationship between floral microbes and flower visitors is highly variable, depending on the combination of microbe and flower visitor species. Furthermore, the plastic behaviours of flower visitors in response to environmental fluctuations make it difficult to predict the relative importance of floral microbes in the interaction between flower visitors and plants and in the evolution of these interactions. This review includes many examples of the diverse effects of floral microbes and should guide readers through the complex and intriguing world of interactions among flower visitors, floral microbes, and plants. I hope that this review will help readers appreciate and be inspired by the huge frontier that remains in this area.

View full abstract

Recent studies have highlighted the presence in various plant organs of diverse microbes that interact closely with plants and affect their life and evolution. However, studies of seed microbes have commenced only recently, although it has long been recognized that certain pathogenic microbes can be transmitted from parent to offspring via seeds. Culture-independent analyses of seed microbial communities have identified “core microorganisms” shared by the seeds of diverse plant species. Seed microbes may colonize the seed through the vascular system of the mother plant or via the external environment, either through the flower or otherwise. Although some seed microbes enhance seedling disease resistance and affect host-seed dormancy, their ecological significance remains largely unexplored. The seed phase is a crucial stage in the plant lifecycle, linking generations and facilitating survival during unfavorable conditions. By studying seed microbes, researchers can gain new insights into the tightly intertwined relationships of plants and microorganisms.

View full abstract

The sensitive plant, Mimosa pudica L., senses external stimuli such as touch and wounding, propagates the information toward the motor organ, the pulvinus, and then moves its leaves within seconds. However, the mechanisms and adaptive significance of the long-distance signal propagation and rapid leaf movements remain unclear. By combining a wide-field, highly-sensitive fluorescence imaging system and an electrophysiological setup, we simultaneously monitored cytosol Ca²⁺ levels and surface potential changes in transgenic M. pudica expressing genetically encoded Ca²⁺ indicators in response to mechanical stimuli. We found that Ca²⁺ signals coupled with electrical signals act as long-distance signals that mediate the rapid leaf movements in M. pudica. Moreover, leaves unable to move rapidly were produced using pharmacological and genetic approaches and we discovered that the leaves unable to move rapidly were more vulnerable to insect attacks than the normal motile leaves. We propose the following model, which illustrates a series of events in the defense response of M. pudica. Insect attacks on leaves generate Ca²⁺ and the electrical signals that propagate toward the pulvini, leading to the Ca²⁺-mediated rapid leaf movements. These movements provide unstable footholds for herbivorous insects and help protect M. pudica against them.

View full abstract

Protists are unicellular eukaryotic organisms, but they show primitive forms of multicellularity as multiple cells move in groups, organize multicellular structures, and share different roles. Their behaviors are expected to be diverse since they still retain the ability to live as single cells in wild habitats. The microenvironment in which they inhabit is neither spatially nor temporally stationary but fluctuates remarkably. For example, when we magnify the environment of a paramecium living in a swamp under a microscope, we can recognize the complexity of spatial shape that combines larger scale and smaller scale irregularities compared to the size of the body. Naturally, there are also other creatures coming and going, water currents, and things constantly flowing in and out. On the other hand, the light environment and temperature environment also fluctuate during the day. The subject here is to what extent they can respond to such a sufficiently complex living environment and how they can respond. In this review, we will introduce the environment-dependent behavioral abilities of protists, mainly focusing on the plasmodial slime mold and additionally mentioning some ciliates.

View full abstract

Filamentous fungi feature a network termed mycelium, comprising chains of elongated cells (hyphae) that repeatedly branch and fuse. In forest ecosystems, filamentous fungi play important roles in the decomposition of plant materials such as dead trees and fallen leaves, and mycorrhizal fungi engage in mutualistic relationships with plant roots. Understanding the development and dynamics of mycelial networks is important when studying material cycling and the inter- and intra-species interactions that sustain forest ecosystems. In this review, we summarize current knowledge on the behavioral characteristics of hyphae and mycelial networks, and the transport of substances and signals from a single hypha to the entire mycelial network. We highlight existing challenges. The tip of an extending hypha features polarity, and thus a memory of the direction of growth, enabling seemingly complex tasks such as maze navigation. It seems that feature-memory and decision-making capacities extend to entire mycelial networks, but the details remain poorly understood. If a fungus is to change its shape and behavior, it must auto-digest unnecessary components and transfer building blocks to newly important regions, but it is unclear how such processes are regulated throughout a mycelial network. Research on mycelial behavior poses many challenges, but progress in network analysis, microfluidic devices, and bioimaging platforms will greatly aid future research.

View full abstract

In recent years, artificial neural networks have become a popular and effective method to analyze various datasets. Due to their high applicability and performance, artificial neural networks are used for purposes such as image data analysis, pattern recognition, and time series analysis, and their applications are expected to expand even further. However, several limitations, such as low interpretability and high learning costs, have been identified, and researchers are developing new methods to overcome these problems. Recently, “Reservoir computing”, a special type of recurrent neural network, has gained attention as a method for archiving high computational performance without significant learning costs. A major part of the learning cost in artificial neural networks stems from the adjustment of weights between nodes that constitute the network, but reservoir computing does not require this weight adjustment, enabling rapid learning. Furthermore, this novel feature of reservoir computing has led to the creation of a new field called physical reservoir computing, which enables physical objects to perform computations. For example, a previous study demonstrated that by outsourcing information processing to the movement of soft, tentacle-like silicon objects, reservoir computing could indeed be implemented in a physical object. Moreover, reservoir computing has begun to be used in ecology, albeit in a small number of studies. In this paper, we explain the concept of reservoir computing and introduce related research on physical reservoir computing. We also discuss relevant ecological studies and explore the potential application of reservoir computing in ecology.

View full abstract

本学術情報では、コロナ禍で行われた新たな生態学教育の手法を概観し、今後どのように活用できるか、ポストコロナの生態学教育を展望した。COVID-19は新たな教育方法を考える契機になった。生態学教育でも同期型・非同期型のオンライン授業が取り入れられた。学生の顔が見えないまま授業を行うことに筆者は抵抗があったが、大講義においては、オンライン授業はコミュニケーションツールとしてむしろ有用であった。同期型でも非同期型でも、オンデマンド授業では、チャットなどのツールを介して学生と一対一のやり取りができるため、対面ではなかなかでない質問が多く寄せられ、クラス全体で共有することができた。生物を観察する実習についても、教員の創意工夫により、オンラインで行う手法が編み出された。冷蔵庫の中の野菜やコメの観察、スーパーで買ってきた魚の解剖、教員から送られてきたブロッコリースプラウトの苗の栽培、という3つの事例を紹介した。演習林や農場などに出向いての調査活動は、オンラインで行うには限界があった。各大学あらゆる感染対策を取ったうえで、対面で行われたケースが多かった。ただし、事前学習や事後学習についてはオンラインを活用した大学もあった。野外での調査活動においても、対面とオンラインの併用は、今後も授業形態の一つとなるだろう。最後に、コロナ禍で培ったオンライン技術のノウハウを、ポストコロナで活用する方法として、大講義での双方向性の担保、教室外からの講義、授業コンテンツの共有、緊急時の対面授業の代替の4つを提案した。

View full abstract