Slime molds are large amoeboid unicellular organisms. Due to the large size of the cell body, it has developed a network of tubes that transport protoplasm throughout the cell body. This allows the slime mold, which has neither a brain nor a nervous system, to exhibit a variety of sophisticated behaviors. The network morphology of the transport tubes changes remarkably depending on the environment. In attractive environments, the slime molds form a fine mesh network; in repulsive environments they form a tree-like structure composed of relatively thick transport tubes. We will discuss that these transport network morphologies are adaptive and reasonable in their respective environments. Additionally, it has been shown that when slime molds are subjected to repetitive temporal or spatial aversive stimuli, they are able to memorize that state for a while. We will discuss the substantial mechanism of this memory from the viewpoint of the transport tube network morphology.

Most swimming algae exhibit photo-induced behavioral change (or photobehavior) to inhabit a light environment suitable for photosynthesis. The unicellular green alga Chlamydomonas reinhardtii is a model organism to study the regulatory mechanisms of ciliary (or flagellar) motility and photoreception for photobehavior. C. reinhardtii belongs to the order Volvocales, which is suggested to have evolved through the multicellularity of an ancestral unicellular species that resembles C. reinhardtii. They include multicellular species of various cell numbers ranging from four (Tetrabaena) to >10,000 (Volvox). Depending on the number of cells and the configuration, the cilia of Volvocales green algae are differently regulated to exhibit photobehavior after photoreception. In this presentation, I will discuss the similarities and differences in the regulatory mechanisms for photobehavior of unicellular C. reinhardtii, four-celled Tetrabaena socialis that forms a planar colony, and 5,000~10,000-celled Volvox rousseletii that forms a spheroidal colony. The physiological significance of photobehavior will also be discussed, given their different survival strategies revealed by this study.

Movement and search in space are essential to the intelligence of living organisms. Over the last two decades, research has reported that organisms, including cells, insects, mammals, and even humans, commonly exhibit a pattern of Lévy walk, a special type of random with step lengths that follow a power-law distribution. In the random search problem framework, which considers how to find a target efficiently (e.g., food, mates, or habitats) in an uncertain environment, it is hypothesized that the Lévy walk leads to high search efficiency. Therefore, many organisms exhibit the Lévy walk due to adaptive evolution. However, there has been a recent debate about the origin of Lévy walks. Some findings suggest that Lévy walks might also be epiphenomena arising from interactions with a complex environment. Thus, why Lévy walks are a common mode of biological movement and how they are generated remain controversial. In this talk, I will review the paradigm of conventional Lévy walk research and then discuss the future direction of research on search behavior and random searches as the basis of biological intelligence.

The chirality or left-right asymmetry of the morphogenesis and arrangement of organ is essential for their function and development. The chirality of organ and tissue is derived from the chirality of the cells that compose of them, and the cellular chirality emerges by organizing the molecular chirality within the cell. However, the principle of how molecular chirality is organized to lead to cellular chirality and how collective chirality in multicellular systems emerges from cellular chirality are still unclear. To address these questions, we first experimentally study the dynamical chiral behaviors of an epithelial cultured cell. Based on the experimental observation, we next develop a theoretical understanding of how the chiral behaviors arise from the molecular-level chirality. We further study the multicellular behavior of this cell and found that it exhibits a collective rotational cell migration in a particular direction. In our study, we establish a connection from molecular scale chirality to multicellular scale chirality.

Simple feedback loops control the shape of flagella bending waves, giving rise to efficient navigation strategies and synchronization. I will present two such feedback loops, which rely chemical and mechanical control signals. I will first discuss how sperm cells find the egg using chemical cues. Sperm cells from marine species swim along helical paths: this active motion traces an oscillating concentration stimulus from an external concentration gradient, with a phase that encodes the direction of the gradient [1]. A simple feedback loop enables the cell to steer its helical path up the gradient and thus towards the egg. This mechanism is robust against parameter variations, noise, and even small-scale turbulence typical for natural habitats [2]. In a second part, I will address how beating flagella respond to mechanical forces, and how this enables synchronization in collections of flagella [3].

[1] J.F. Jikeli et al.: Sperm navigation along helical paths in 3D chemoattractant landscapes, Nature Communications 6, 2015

[2] S. Lange et al.: Sperm chemotaxis in marine species is optimal at physiological flow rates according theory of filament surfing, PLoS Comp. Biol., 17(4): e1008826, 2021

[3] A. Solovev et al.: Synchronization in cilia carpets …, New J Physics 24:013015, 2021

Cilia are ubiquitous, hair-like protrusions attached to cells. Interactions between cilia and ciliated tissues mediate a variety of physiological flows. Whenever multiple cilia exist in close proximity they will invariably interact, leading to the emergence of many types of local and global coordination patterns. Often, the mechanism of this interaction or coupling is mysterious and highly system-dependent. Adjacent cilia can communicate physically through the fluid, but they can also do so via elastic or cytoskeletal linkages through the cell or tissue surface. In this talk we will consider the strategies and consequences of distinct modes of ciliary coordination and propulsion in diverse organisms. We will introduce different model systems in which groups of cilia can move completely synchronously, maintain specific synchronization patterns, or else beat metachronously along topologically interesting structures. We will also discuss how ciliary arrays select different modes of synchrony or metachrony, transitioning stochastically between order and disorder, and the implications of this for whole-organism self-propulsion and navigation in the vast depths of the ocean.