Biology subjects

Sasaki, A.

Publications and source records attributed to Sasaki, A..

25 records · Page 2Linked to original sources

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↗

bioRxiv2021

Multi-morph eco-evolutionary dynamics in structured populations

Our understanding of the evolution of quantitative traits in nature is still limited by the challenge of including realistic trait distributions in the context of frequency-dependent selection and ecological feedbacks. We extend to class-structured populations a recently introduced "oligomorphic approximation" which bridges the gap between adaptive dynamics and quantitative genetics approaches and allows for the joint description of the dynamics of ecological variables and of the moments of multimodal trait distributions. Our theoretical framework allows us to analyse the dynamics of populations composed of several morphs and structured into distinct classes (e.g. age, size, habitats, infection status, species...). We also introduce a new approximation to simplify the eco-evolutionary dynamics using reproductive values. We illustrate the effectiveness of this approach by applying it to the important conceptual case of two-habitat migration-selection models. In particular, we show that our approach allows us to predict both the long-term evolutionary endpoints and the short-term transient dynamics of the eco-evolutionary process, including fast evolution regimes. We discuss the theoretical and practical implications of our results and sketch perspectives for future work.

evolutionary biology↗

bioRxiv2021

The impact of antigenic escape on the evolution of virulence

Understanding the evolutionary drivers determining the transmission rate and virulence of pathogens remains an important challenge for evolutionary theory with clear implications to the control of human, agricultural and wildlife infectious disease. Although disease is often very dynamic, classical theory examines the long-term outcome of evolution at equilibrium and, in simple models, typically predicts that R0 is maximized. For example, immune escape may lead to complex disease dynamics including repeated epidemics, fluctuating selection and diversification. Here we model the impact of antigenic drift and escape on the evolution of virulence and show analytically that these non-equilibrium dynamics select for more acute pathogens with higher virulence. Specifically, under antigenic drift and when partial cross immunity leads to antigenic escape, our analysis predicts the long-term maximization of the intrinsic growth rate of the parasite resulting in more acute and virulent pathogens than those predicted by classic R0 maximization. Furthermore, it follows that these pathogens will have a lower R0 leading to implications for epidemic, endemic behavior and control. Our analysis predicts both the timings and outcomes of antigenic shifts leading to repeated epidemics and predicts the increase in variation in both antigenicity and virulence before antigenic escape. There is considerable variation in the degree of antigenic escape that occurs across pathogens and our results may help to explain the difference in virulence between related pathogens most clearly seen in the human A, B and C influenzas. More generally our results show the importance of examining the evolutionary consequences of non-equilibrium dynamics.

evolutionary biology↗

bioRxiv2020

Maternal high fat diet alters lactation-specific miRNA expression and programs the DNA methylome in the amygdala of female offspring

Adverse maternal diets high in saturated fats are associated with impaired neurodevelopment and epigenetic modifications in offspring. Maternal milk, the primary source of early life nutrition in mammals, contains lactation-specific microRNAs (miRNAs). Lactation-specific miRNAs have been found in various offspring tissues in early life, including the brain. We examined the effects of maternal high saturated fat diet (mHFD) on lactation-specific miRNAs that inhibit DNA methyltransferases (DNMTs), enzymes that catalyze DNA methylation modifications, in the amygdala of female offspring during early life and adulthood. Offspring exposed to mHFD showed reduced miR-148/152 and miR-21 transcripts in stomach milk and amygdala in the first week of life. This was associated with increased DNMT1 expression, DNMT activity, and global DNA methylation in the amygdala. In addition, persistent DNA methylation modifications from early life to adulthood were observed in pathways involved in neurodevelopment as well as genes regulating the DNMT machinery and protein function in mHFD offspring. The findings indicate a novel link between exogenous, lactation-specific miRNAs and developmental programming of the neural DNA methylome in offspring.

molecular biology↗

bioRxiv2020

Development of Microsatellite Markers for a Soricid Water Shrew Chimarrogale platycephalus, and the Success of Individual Identification Using It.

The soricid water shrew, Chimarrogale platycephalus, is a mammal species endemic to the Japanese Islands. They inhabit the islands of Honshu and Kyushu, and are considered to be extinct in Shikoku. Information on this water shrew from Honshu and Kyushu is also scarce, and C. platycephalus is registered on the Japanese Governments red list as an endangered species. Almost all study areas such as regarding their ethology, ecology, also their phylogenetics are lacking. The delay in these foundational studies is due to difficulties related to them being both nocturnal and aquatic. In order to study of C. platycephalus, it is essential to conduct field research in mountain streams at night under such circumstances. In response to such difficult circumstances, we established a genetic analysis method using the feces of C. platycephalus, and as a result the accumulation of data on their phylogenetic evolution and phylogeography has increased which has improved our understanding of this species. Furthermore in this study, development of microsatellite markers was carried out, and a total of 21 loci marker analyses were performed. In addition, in order to confirm the credibility of these 21 microsatellite markers, as being able to validly differentiate individuals, all markers were examined using the fecal and tissues specimens from verified separately reared individuals (12 individuals) with the known history of having been reared in an aquarium. As a result, it was revealed that if analyses of the 12 loci were possible, individual differentiation with 100% accuracy was possible. The development of microsatellite markers in this study, and the establishment of individual identification methods by means of this will be expected to greatly contribute to future ecological and ethological research, population genetics and biogeographical research of the water shrew, C. platycephalus.

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↗

bioRxiv2019

Maternal high-fat diet induces sex-specific effects on inflammatory responses to corticosterone and lipopolysaccharide challenge in adult rat offspring

BackgroundAcute elevations in endogenous corticosterone (CORT) with psychosocial stress or exogenous administration potentiate inflammatory gene expression. Maternal obesity as a result of high-fat diet (HFD) consumption has been linked to higher basal levels of neuroinflammation, including increased expression of pro-inflammatory genes in the amygdala. These findings suggest that exposure to maternal HFD may elicit pro-inflammatory responses in the presence of an immune stressor such as lipopolysaccharide (LPS), a component of gram-negative bacteria, as well as acute elevated CORT. MethodsRat offspring were exposed to maternal HFD or control diet (CHD) throughout pre and postnatal development until weaning, when all offspring were provided CHD until adulthood. In adulthood, offspring were challenged with administration of exogenous CORT, to simulate an acute physiological stress, LPS, to induce an immune stress, or both. qPCR was used to measure transcript abundance of CORT receptors and downstream inflammatory genes in the amygdala, hippocampus and prefrontal cortex, brain regions that mediate neuroendocrine and behavioral responses to stress. ResultsHFD female offspring exhibited elevations in anti-inflammatory transcripts, whereas HFD male offspring responded with greater pro-inflammatory gene expression to simultaneous CORT and LPS administration. ConclusionsThese findings suggest that exposure to maternal HFD leads to sex-specific alterations that may alter inflammatory responses in the brain, possibly as an adaptive response to basal inflammation.

neuroscience↗