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Variability in space use among conspecifics can emerge from foraging strategies that track available resources, especially in riverscapes that promote high synchrony between prey pulses and consumers. Projected changes in riverscape hydrological regimes due to water management and climate change accentuate the need to understand the natural variability in animal space use and its implications for population dynamics and ecosystem function. Here, we used long-term tracking of Common Snook (Centropomus undecimalis) movement and trophic dynamics in the Shark River, Everglades National Park from 2012 to 2023 to test how specialization in the space use of individuals (i.e., Eadj) changes seasonally, how it is influenced by yearly hydrological conditions, and its relationship to the between individual trophic niche. Snook exhibited seasonal variability in space use, with maximum individual specialization (high dissimilarity) in the wet season. The degree of individual specialization increased over the years in association with greater marsh flooding duration, which produced important subsidies. Also, there were threshold responses of individual space use specialization as a function of floodplain conditions. Greater specialization in space use results in a decrease in snook trophic niche size. These results show how hydrological regimes in riverscapes influence individual specialization of resource use (both space and prey), providing insight into how forecasted hydroclimatic scenarios may shape habitat selection processes and the trophic dynamics of mobile consumers. 

ABSTRACT ObjectiveEnvironmental variability as a factor of climate change and water management can result in fluctuations in the abundance and distribution of fish populations from year to year, with either negative or positive effects depending on behavioral and physiological requirements and the ability to adapt to changing conditions. Variability in water levels can also influence prey availability, affecting predator abundance in seasonal foraging areas. In this study, our objective was to better understand how environmental variation has affected the relative abundance of Common Snook Centropomus undecimalis in the freshwater/estuarine habitats of Everglades National Park. MethodsElectrofishing data over 17 years (2004–2021) were analyzed in relation to a long-term time-series of environmental conditions, including water level, temperature, salinity, and precipitation. We used seasonal and trend decomposition via locally estimated scatterplot smoothing to isolate the effect of seasonality and identify nonlinear trends in the environmental time-series data and Common Snook abundance and Mann–Kendall trend tests to identify monotonic and directional trends over time. To identify the factors that best explain variation in Common Snook abundance, we used generalized linear models to relate relative abundance to the environmental covariates. ResultsWe found significant long-term trends of increasing water level and temperature and decreasing salinity in the study area. The generalized linear models indicated that Common Snook abundance had a negative relationship with water level and a positive relationship with temperature. Common Snook abundance over the 17 years of sampling was relatively stable; however, increases/decreases in Common Snook abundance corresponded to both seasonal changes in water level and the periodic occurrence of extreme conditions (e.g., cold spells, droughts, prolonged dry-season flooding). ConclusionsUnderstanding how past environmental change has affected fish populations can provide insight into how they may respond to future conditions. Our results suggest that water management decisions that maintain seasonal patterns of high/low water levels can potentially mitigate climate-driven shifts by providing conditions that promote prey production in the wet season and foraging opportunities in the dry season, increasing the relative abundance of ecologically and recreationally important species such as Common Snook. 

Numerous species face redistribution and compression of habitat due to climate change. Compounded with anthropogenic stressors, coastal systems are among those experiencing the largest shifts in distribution and degradation of habitats. We coupled long-term movement and environmental data to assess how a freshwater species responds to changes in a coastal refuge habitat to quantify distributional changes, identify key environmental variables, and provide restoration targets. Salinity, variation in salinity, and stage of surrounding marsh habitat were the most important variables driving Florida bass (Micropterus salmoides) occurrence in the estuary. Salinity below 8.7 ppt had the largest positive effect on Florida bass occurrence, while low levels of daily variation in salinity (< 1.3 SD) and marsh stages between 11.4 and 27.7 cm were associated with an increased probability of Florida bass occurrence. Years with above average freshwater inputs that shifted mesohaline boundaries downstream generated 15.3 km2 of both core and conditional habitat for Florida bass, average conditions generated 4.4 km2 of core and conditional habitat, whereas dry conditions compressed Florida bass habitat to 1.7 km2. These results suggest that varying environmental scenarios can shift the amount of suitable habitat available for freshwater species using conditional coastal habitats. Our study provides salinity and marsh depth thresholds that offer actionable management targets to maximize the presence of Florida bass in coastal rivers, with population and fishing quality benefits. Climate change will likely result in large-scale reductions of critical dry season habitat for these species, while restoration efforts and adaptive management can bolster the resiliency of these habitats. 

ABSTRACT Themaintenance ofcarboxysomedistribution (Mcd) system comprises the proteins McdA and McdB, which spatially organize carboxysomes to promote efficient carbon fixation and ensure their equal inheritance during cell division. McdA, a member of the ParA/MinD family of ATPases, forms dynamic gradients on the nucleoid that position McdB-bound carboxysomes. McdB belongs to a widespread but poorly characterized class of ParA/MinD partner proteins, and the molecular basis of its interaction with McdA remains unclear. Here, we demonstrate that the N-terminal 20 residues ofH. neapolitanusMcdB are both necessary and sufficient for interaction with McdA. Within this region, we identify three lysine residues whose individual substitution modulates McdA binding and leads to distinct carboxysome organization phenotypes. Notably, lysine 7 (K7) is critical for McdA interaction: substitutions at this site result in the formation of a single carboxysome aggregate positioned at mid-nucleoid. This phenotype contrasts with that of an McdB deletion, in which carboxysome aggregates lose their nucleoid association and become sequestered at the cell poles. These findings suggest that weakened McdA–McdB interactions are sufficient to maintain carboxysome aggregates on the nucleoid but inadequate for partitioning individual carboxysomes across it. We propose that, within the ParA/MinD family of ATPases, cargo positioning and partitioning are mechanistically separable: weak interactions with the cognate partner can mediate positioning, whereas effective partitioning requires stronger interactions capable of overcoming cargo self-association forces. 

Optically anisotropic materials are sought after for tailoring the polarization of light. Recently, colossal optical anisotropy (Δn = 2.1) was reported in a quasi-one-dimensional chalcogenide, Sr9/8TiS3. Compared to SrTiS3, the excess Sr in Sr9/8TiS3 leads to periodic structural modulations and introduces additional electrons, which undergo charge ordering on select Ti atoms to form a highly polarizable cloud oriented along the c-axis, hence resulting in the colossal optical anisotropy. Here, further enhancement of the colossal optical anisotropy to Δn = 2.5 in Sr8/7TiS3 is reported through control over the periodicity of the atomic-scale modulations. The role of structural modulations in tuning the optical properties in a series of SrxTiS3 compounds with x = [1, 9/8, 8/7, 6/5, 5/4, 4/3, 3/2] is investigated using density-functional-theory (DFT) calculations. The structural modulations arise from various stacking sequences of face-sharing TiS6 octahedra and twist-distorted trigonal prisms and are found to be thermodynamically stable for 1 < x < 1.5. As x increases, an indirect-to-direct band gap transition is predicted for x ≥ 8/7 along with an increased occupancy of Ti-dz2 states. Together, these two factors result in a theoretically predicted maximum birefringence of Δn = 2.5 for Sr8/7TiS3. Single crystals of Sr8/7TiS3 were grown using a molten-salt flux method. Single-crystal X-ray diffraction measurements confirm the presence of long-range order with a periodicity corresponding to Sr8/7TiS3, which is further corroborated by atomic-scale observations using scanning transmission electron microscopy. Polarization-resolved Fourier-transform infrared spectroscopy of Sr8/7TiS3 crystals shows Δn ≈ 2.5, in excellent agreement with the theoretical predictions. Overall, these findings demonstrate the compositional tunability of optical properties in SrxTiS3 compounds by control over atomic scale modulations and suggest that similar strategies could be extended to other compounds having modulated structures.