Biology subjects

Ito, H. C.

Publications and source records attributed to Ito, H. C..

6 recordsLinked to original sources

bioRxiv2026

Evolutionary branching under slowly evolving constraints

Biological populations have been evolving in multi-dimensional trait spaces. Ecological interactions can induce the evolutionary diversification of a biological population into distinct multiple populations, which is called evolutionary branching in adaptive dynamics theory. If possible mutations are restricted to certain directions due to developmental, physiological, or physical constraints, the resulting evolutionary dynamics may be restricted to subspaces with fewer dimensions than the original trait spaces. In general, such constraints are also evolving slowly, due to rare and slight mutational deviations from the constraint subspaces. In this sense, constraints are not strict. However, the method for describing non-strict constraints that is globally consistent has yet to be developed. This study proposes a general and flexible method for constructing a non-strict constraint subspace from the corresponding strict constraint subspace. This method enables efficient analysis of adaptive evolution including evolutionary branching under non-strict constraints in the framework of adaptive dynamics theory. Applying this method to a resource competition model shows that the shape of the carrying capacity distribution can be treated as a non-strict constraint curve, and that the likelihood of evolutionary branching is affected not only by the shape of the constraint curve but also by its slow evolution.

evolutionary biology↗

bioRxiv2025

Evolutionary branching points in multi-dimensional trait spaces

Ecological interactions play a crucial role in driving speciation and adaptive radiation. According to the adaptive dynamics theory of evolution in one-dimensional trait spaces, such evolutionary diversifications can occur when evolutionary branching points (convergence stable and evolutionarily unstable singular points) exist in the trait spaces. However, these evolutionary diversifications may occur across multiple traits at once, as exemplified by various within-species ecotypic diversifications involving multiple traits or genes. This paper attempt to extend this branching point condition to evolution in multi-dimensional trait spaces. Two criteria, termed branching possibility and branching inevitability, are developed to evaluate the likelihood of evolutionary branching in multi-dimensional trait spaces. Branching possibility guarantees the existence of evolutionary pathways that lead to branching (where deterministic parts of these pathways are described with the canonical equation of adaptive dynamics theory). Branching inevitability guarantees a steady progression of evolutionary branching (where the progression degree is described with a time-increasing function related to the local Lyapunov function, the potential function in an evolutionary potential game, and Fisher's fundamental theorem). Numerically simulated evolution in multi-dimensional trait spaces show that points having branching possibility or inevitability can induce evolutionary branching not only under asexual reproduction but also under sexual reproduction.

evolutionary biology↗

bioRxiv2024

Growth regulation bringing modularity to morphogenesis of complex three-dimensional exoskeletons

Diverse three-dimensional morphologies of arthropods appendages, including beetle horns, are formed through the non-uniform growth of epidermis. Prior to moulting, epidermal tissue peels off from the old cuticle and grows non-uniformly to shape protruding appendages, which are often branching, curving, or twisting, from the planar epidermis. This non-uniform growth is possibly regulated by the distribution of morphogens on the epidermal cell sheet. Previous studies have identified molecules and signalling pathways related to such morphogenesis; however, how local regulation of cell sheet growth can transform planar epidermis globally into complex three-dimensional structures, such as beetle horns, remains unclear. To reveal the relationship between epidermal growth regulation and generated structures, this study theoretically examined how various shapes can be generated from planar epidermis under a deductive growth model that corresponds morphogen distributions to non-uniform growth on tissue. The results show that the heterochronic expression of multiple morphogens can flexibly fuse multiple simple shapes to generate various structures emulating complex appendages of beetles. These findings indicate that morphogenesis through such a mechanism may have developmental stability and modularity, providing insights into the evolution of the diverse morphology of arthropods.

evolutionary biology↗

bioRxiv2021

The adaptation front equation explains diversification hotspots and living-fossilization

Taxonomic turnovers are common in the evolutionary histories of biological communities. Such turnovers are often associated with the emergence and diversification of groups that have achieved fundamental innovations beneficial in various ecological niches. In the present study, we show that such innovation-driven turnovers could be analyzed using an equation that describes the dynamics of zero-fitness isoclines in a two-dimensional trait space comprising a "fundamental trait" (describing fundamental innovation) and a "niche trait" (describing niche position) or with its higher-dimensional extensions. Our equation allows analytical prediction of evolutionary source-sink dynamics along the niche axis for an arbitrary unimodal (or multimodal with weak separation) carrying capacity distribution. The prediction was confirmed by numerical simulation under different assumptions for resource competition, reproduction, and mutation. In the simulated evolution, biodiversity sources are the central niches having higher carrying capacities than the outer niches, allowing species there the faster evolutionary advancement in fundamental traits and their repeated diversification into outer niches, which outcompete the indigenous less advanced species. The outcompeted species go extinct or evolve directionally toward the far outer niches of the far slower advancement because of the far lower carrying capacities. In consequence of this globally acting process over niches, species occupying peripheral (i.e., the outermost) niches can have significantly primitive fundamental traits and deep divergence times from their closest relatives, and thus, they correspond to living fossils. The extension of this analysis for multiple geographic regions showed that living fossils are also expected in geographically peripheral regions for the focal species group. Significance StatementWe developed a new equation for analyzing the long-term coevolution of many species through their directional evolution, evolutionary branching, and extinction in an arbitrary trait space comprising traits describing niche positions and traits describing fundamental innovations. This equation describes the many coevolving species as a fluid, as in the study of galaxy dynamics in astronomical physics. This equation may be used to explain how innovation-driven taxonomic turnovers generate diversification hotspots and coldspots among niches or geographical regions, accompanied by continuous production of "living fossil" species in peripheries, in a logic equivalent to that deduced by Darwin and Darlington from empirical observations.

evolutionary biology↗

bioRxiv2019

Evolutionary branching of function-valued traits under constraints

Some evolutionary traits are described by scalars and vectors, while others are described by continuous functions on spaces (e.g., shapes of organisms, resource allocation strategies between growth and reproduction along time, and effort allocation strategies for continuous resource distributions along resource property axes). The latter are called function-valued traits. This study develops conditions for candidate evolutionary branching points, referred to as CBP conditions, for function-valued traits under simple equality constraints, in the framework of adaptive dynamics theory (i.e., asexual reproduction and rare mutation are assumed). CBP conditions are composed of conditions for evolutionary singularity, strong convergence stability, and evolutionary instability. The CBP conditions for function-valued traits are derived by transforming the CBP conditions for vector traits into those for infinite-dimensional vector traits.

evolutionary biology↗

bioRxiv2019

Evolutionary branching in distorted trait spaces

Biological communities are thought to have been evolving in trait spaces that are not only multi-dimensional, but also distorted in a sense that mutational covariance matrices among traits depend on the parental phenotypes of mutants. Such a distortion may affect diversifying evolution as well as directional evolution. In adaptive dynamics theory, diversifying evolution through ecological interaction is called evolutionary branching. This study analytically develops conditions for evolutionary branching in distorted trait spaces of arbitrary dimensions, by a local nonlinear coordinate transformation so that the mutational covariance matrix becomes locally constant in the neighborhood of a focal point. The developed evolutionary branching conditions can be affected by the distortion when mutational step sizes have significant magnitude difference among directions, i.e., the eigenvalues of the mutational covariance matrix have significant magnitude difference.

evolutionary biology↗