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1. The 230 GHz Variability of Numerical Models of Sagittarius A*. II. The Physical Origins of the Variability

   https://doi.org/10.3847/1538-4357/adc99f  

   Chan, Ho-Sang; Chan, Chi-kwan (May 2025, The Astrophysical Journal)

   Abstract We continue our previous work, H.-S. Chan et al., to investigate how variations in the electron temperature prescription parameter,R_Low, influence the 3 hr variability at 230 GHz,M_ΔT, in magnetically arrested disk (MAD) models of Sagittarius A* (Sgr A*), through analyzing a series of general-relativistic magnetohydrodynamics and ray-tracing simulations. For models with a black hole spina > 0, we discovered that increasingR_Lowrenders the photon ring more optically thick, obscuring the varying accretion flows that contribute to the variability. However, asR_Lowincreases further, MAD flux eruptions become more pronounced, compensating for the decrease inM_ΔT. For models with spina < 0, although a higherR_Lowalso increases the optical thickness of the fluid, voids within the optically thick gas fail to cover the entire photon ring. Similarly, flux eruptions become more prominent asR_Lowincreases further, contributing to the observed rise inM_ΔTrelative toR_Low. For black holes with spina= 0, although the effect of increasing optical depth is still present, their 230 GHz light curves, and henceM_ΔT, are insensitive to changes inR_Low. Furthermore, we found that the variability of the 230 GHz light curves atR_Low = 1 might correlate with fluctuations in the internal energy of the gas near the black hole, and we listed potential causes and solutions to the over-variability problem. Our findings highlight potential approaches for refiningM_ΔTto better align with observations when modeling Sgr A*. 

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2. The dual nature of metacommunity variability

   https://doi.org/10.1111/oik.08517  

   Lamy, Thomas; Wisnoski, Nathan I.; Andrade, Riley; Castorani, Max C.; Compagnoni, Aldo; Lany, Nina; Marazzi, Luca; Record, Sydne; Swan, Christopher M.; Tonkin, Jonathan D.; et al (August 2021, Oikos)

   null (Ed.)
3. Sex and the Riddle of Variability

   https://doi.org/10.3998/ptpbio.5492  

   Richardson, Sarah S (June 2025, Philosophy, Theory, and Practice in Biology)

   Scientific research associations, funders, and publishers have recently introduced sex inclusion mandates requiring the use of male and female specimens in preclinical research designs and the analysis and reporting of data disaggregated by sex. However, it is not necessarily a simple matter to incorporate males and females in the same study design with the aim of detecting differences between them while following best practices for rigorous inference in laboratory science using model organisms. For example, if there are ways in which male and female variability might differ for the trait or procedure of interest, principles of sound experimental design may require larger numbers of organisms and observations to make valid inferences about the presence of a sex difference. This paper analyzes a current scientific debate over differences in variability between male and female laboratory rodents, and specifically over whether potential sources of sex-specific variability such as the estrous cycle, group housing, and body size constitute components of sex that should be measured. The variability debate surfaces the trade-offs between constructs of sex difference and similarity that face scientific researchers attempting to meet mandates to include both males and females in research design and report sex-specific results. This riddle of variability illuminates how laboratory researchers using model organisms must make contextual choices (Richardson 2022) at multiple decision points in order to stabilize sex as a biological variable in a particular research design. These judgments are informed by social and epistemic values and carry consequences for the validity, precision, and generalizability of claims of biological sex differences derived from preclinical research models. 

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4. The variability of evolvability: Properties of dynamic fitness landscapes determine how phenotypic variability evolves

   https://doi.org/10.1073/pnas.2519469122  

   Petak, Csenge; Frati, Lapo; Vroomans, Renske_M A; Pespeni, Melissa H; Cheney, Nick (December 2025, Proceedings of the National Academy of Sciences)

   The magnitude and shape of phenotypic variation depends on properties of the genotype-to-phenotype (GP) map, which itself can evolve over time. The evolution of GP maps is particularly interesting in variable environments, as GP maps can evolve to bias variation in the direction of past selection, increasing the evolvability of the population over time. However, the degree and manner in which environmental variation shapes GP maps and influences evolutionary dynamics may depend on properties of the fitness landscape. To explore how evolutionary dynamics are affected by variable environments across a wide range of different pairs of fitness landscapes, we evolved GP maps to produce spatial-temporal gene expression patterns that matched two-dimensional patterns generated by different elementary cellular automata rules. We found remarkable variation in how populations evolved in variable environments. In some cases, changing the environment helped populations find higher fitness peaks; in others, it hindered them. The evolution of evolvability also depended on the fitness landscape pair. In some experiments, the ability to generate adaptive phenotypic variation upon environment change increased over time, while in some others, populations found shared areas between fitness landscapes. On the other hand, environmental variability consistently resulted in higher fitness landscape exploration, average fitness, and mutational robustness compared to evolution in static environments, which we hypothesize are tightly connected. In conclusion, work presented here sheds light on important general consequences of environmental variability, while also demonstrating dependency on properties of fitness landscapes, which future research on the evolution of evolvability should consider. 

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5. Hypolimnetic Hypoxia Increases the Biomass Variability and Compositional Variability of Crustacean Zooplankton Communities

   https://doi.org/10.3390/w11102179  

   Doubek, Jonathan P.; Campbell, Kylie L.; Lofton, Mary E.; McClure, Ryan P.; Carey, Cayelan C. (October 2019, Water)

   In freshwater lakes and reservoirs, climate change and eutrophication are increasing the occurrence of low-dissolved oxygen concentrations (hypoxia), which has the potential to alter the variability of zooplankton seasonal dynamics. We sampled zooplankton and physical, chemical and biological variables (e.g., temperature, dissolved oxygen, and chlorophyll a) in four reservoirs during the summer stratified period for three consecutive years. The hypolimnion (bottom waters) of two reservoirs remained oxic throughout the entire stratified period, whereas the hypolimnion of the other two reservoirs became hypoxic during the stratified period. Biomass variability (measured as the coefficient of the variation of zooplankton biomass) and compositional variability (measured as the community composition of zooplankton) of crustacean zooplankton communities were similar throughout the summer in the oxic reservoirs; however, biomass variability and compositional variability significantly increased after the onset of hypoxia in the two seasonally-hypoxic reservoirs. The increase in biomass variability in the seasonally-hypoxic reservoirs was driven largely by an increase in the variability of copepod biomass, while the increase in compositional variability was driven by increased variability in the dominance (proportion of total crustacean zooplankton biomass) of copepod taxa. Our results suggest that hypoxia may increase the seasonal variability of crustacean zooplankton communities. 

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