Biology subjects

Toyama, K. S.

Publications and source records attributed to Toyama, K. S..

6 recordsLinked to original sources

bioRxiv2025

Algae-specific Immune Modulation Influences Responses to Heat and Pathogen Challenge in a Symbiotic Coral

The role of symbiotic algae in coral life history and host health is well documented, but the immune and physiological trade-offs of hosting these symbionts remain less explored. While association with the algal symbionts of the genus Durusdinium is known to confer thermotolerance, it has also been linked to coral tissue loss under stress. We investigated whether algal type influences host immunity and stress responses in the tropical coral Pocillopora acuta. Durusdinium-hosting (D-hosting) P. acuta have distinct transcriptomic profiles, higher immune-related gene expression, and elevated baseline levels of immunity transcription factor NF-{kappa}B as compared to corals hosting Cladocopium (C-hosting). Under heat challenge, D-hosting P. acuta exhibited tissue loss, oxidative stress, immune and microbial dysregulation, whereas C-hosting P. acuta were more susceptible to bleaching, metabolic dysregulation, and decline in nitrogen-fixing and antioxidant-producing bacteria. Finally, infection with the the bacterium Vibrio coralliilyticus caused high tissue loss in D-hosting corals, but not in C-hosting corals. Our results suggest a mechanism for how Durusdinium association enhances thermotolerance yet predisposes corals to tissue damage under stress, suggesting immune trade-offs that can compromise host survival under multiple stressors.

genomics↗

bioRxiv2024

Antibiotic treatment and microbiome depletion slow cnidarian regeneration

Cnidarian microbiomes play an essential role in physiology and development, but how these communities influence tissue regeneration is poorly understood. Here, we examined the effects of antibiotic exposure on regeneration and microbial communities in two cnidarian models, the sea anemones Nematostella vectensis (non-symbiotic, hereafter, Nematostella) and Exaiptasia pallida (symbiotic, hereafter, Aiptasia). Bisected animals were incubated in either sterile or antibiotic-containing artificial seawater for seven days and regeneration was monitored daily. After seven days, tentacle number and length were measured, and microbial communities were profiled using metabarcoding of the V4 region of the 16S rRNA. Microbiome disruption was observed under antibiotic treatment in both species, resulting in decreased microbial load and shifts in relative abundances of some microbial taxa. However, Nematostella exhibited a greater reduction in microbial diversity and community shifts under antibiotic exposure, whereas Aiptasia showed only moderate changes in diversity. In both species, microbiome disruption was associated with slower regeneration rates and reduced tentacle number and length, suggesting a functional role for the microbiome in cnidarian regeneration. Our findings suggest that host-microbiome interactions in both symbiotic and aposymbiotic anemones are important for the maintenance of regenerative processes. These findings provide insight into how cnidarians and their microbiomes respond to environmental stressors, with implications for predicting cnidarian resilience in the context of emerging threats to the marine environment.

developmental biology↗

bioRxiv2024

Beyond size dimorphism: the past, present, and future of Rensch's Rule

Renschs Rule is known as a pattern of allometry in which the degree of male-biased sexual size dimorphism (SSD) increases with species body size. Over the last decades, a growing amount of Renschs Rule studies has advanced our understanding of SSD, its prevalence in nature, and the mechanisms underlying its evolution. However, Bernhard Rensch, when describing the pattern for the first time, considered the allometry of SSD only as a special case of a more general pattern in which dimorphism in any relative sexual difference increased with body size. In this perspective I revisit the history of Renschs Rule, starting with its popularization in recent decades, then diving into the original works by Rensch to rediscover his original observations, and finally discussing the implications of studying Renschs pattern beyond its applications to SSD. The strong bias towards body size in the study of Renschs Rule has proven valuable regarding our understanding of the evolution of SSD. Using empirical examples I propose, however, that expanding the study of the pattern to other traits might prove insightful for the general study of sexual dimorphism and phenotypic diversity.

evolutionary biology↗

bioRxiv2023

JNplots: an R package to visualize outputs from the Johnson-Neyman technique for categorical and continuous moderators, including options for phylogenetic regressions.

The analysis of two-way interactions in linear models is common in the fields of ecology and evolution, being often present in allometric, macroevolutionary, and experimental studies, among others. However, the interpretation of significant interactions can be incomplete when limited to the examination of model coefficients and significance tests. The Johnson-Neyman technique represents a step forward in the interpretation of significant two-way interactions, allowing the user to examine how changes in the moderator variable, it being categorical or continuous, affect the significance of the relationship between the dependent variable and the predictor. Despite its implementation in several software since its initial development, the available options to perform the method lack certain functionality aspects, including the visualization of regions of non-significance when the moderator is categorical, the implementation of phylogenetic corrections, and more intuitive graphical outputs. Here I present the R package JNplots, which aims to fill gaps left by previous software regarding the calculation and visualization of regions of non-significance when fitting two-way interaction models. JNplots includes two basic functions which allow the user to investigate different types of interaction models, including cases where the moderator variable is categorical or continuous. The user can also specify whether the model to explore should be phylogenetically informed and choose a particular phylogenetic correlation structure to be used. Finally, the functions of JNplots produce plots that are largely customizable and allow a more intuitive interpretation of the interaction term. Here I provide a walkthrough on the use of JNplots using three different examples based on empirical data, each representing a different common scenario in which the package can be useful. Additionally, I present the different customization options for the graphical outputs of JNplots.

evolutionary biology↗

bioRxiv2022

Bergmann's rule in Microlophus lizards: testing for latitudinal and climatic gradients of body size.

Broadscale environmental gradients exert selection pressures that can result in macroevolutionary patterns of phenotypic diversity. Bergmanns rule, one of the most studied ecogeographical patterns, states that among related species or populations, larger body sizes should occur at higher latitudes or colder climates given the efficacy of larger sizes to conserve heat. However, there is still much debate regarding the mechanisms that underlie the rule and whether they should be different between endotherms and ectotherms. Here we test for Bergmanns rule in Microlophus lizards, a genus distributed in western South America and the Galapagos Islands, and test for associations between body size and climatic variables. Our results indicate that mainland Microlophus species follow Bergmanns rule, meaning that larger species are found towards the southernmost latitudes encompassed by the genus distribution. This relationship was similar for males and females, suggesting that patterns of sexual size dimorphism are not driven by differing latitudinal gradients of body size between the sexes. We identified negative associations between body size and temperature, precipitation, and isothermality, meaning that larger species are found in colder, drier, and more thermally variable environments. We discuss the possible mechanisms behind this pattern, the implications of insularity and ecology for the evolution of body size in this genus, and emphasize the need for additional natural history information to allow for the elucidation of the mechanisms behind the patterns presented in this work.

evolutionary biology↗

bioRxiv2021

A simple hierarchical model for heterogeneity in the evolutionary correlation on a phylogenetic tree

Numerous questions in phylogenetic comparative biology revolve around the correlated evolution of two or more phenotypic traits on a phylogeny. In many cases, it may be sufficient to assume a constant value for the evolutionary correlation between characters across all the clades and branches of the tree. Under other circumstances, however, it is desirable or necessary to account for the possibility that the evolutionary correlation differs through time or in different sections of the phylogeny. Here, we present a method designed to fit a hierarchical series of models for heterogeneity in the evolutionary rates and correlation of two quantitative traits on a phylogenetic tree. We apply the method to two datasets: one for different attributes of the buccal morphology in sunfishes (Centrarchidae); and a second for overall body length and relative body depth in rock- and non-rock-dwelling South American iguanian lizards. We also examine the performance of the method for parameter estimation and model selection using a small set of numerical simulations.

evolutionary biology↗