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Social defeat is a powerful experience leading to drastic changes in physiology and behavior, many of which are negative. For example, repeated social defeat in vertebrates results in reduced reproductive success, sickness and behavioral abnormalities that threaten individual survival and species persistence. However, little is known about what neural mechanisms are involved in determining whether an individual is resilient or susceptible to repeated social defeat stress. It also remains unknown whether exclusive use of reactive behaviors after repeated social defeat is maintained over time and impacts future behaviors during subsequent contests. We used a resident-intruder experiment in the African cichlid fish Astatotilapia burtoni to investigate the behavior and neural correlates of these two opposing groups. Behavior was quantified by watching fish during defeat trials and used to distinguish resilient and susceptible individuals. Both resilient and susceptible fish started with searching and freezing behaviors, with searching decreasing and freezing increasing after repeated social defeat. After a 4 day break period, resilient fish used both searching and freezing behaviors during a social defeat encounter with a new resident, while susceptible fish almost exclusively used freezing behaviors. By quantifying neural activation using pS6 in socially relevant brain regions, we identified differential neural activation patterns associated with resilient and susceptible fish and found nuclei that co-varied and may represent functional networks. These data provide the first evidence of specific conserved brain networks underlying social stress resilience and susceptibility in fishes.

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Thermal tolerance greatly influences the geographic distribution, seasonality, and feeding habits of mosquitoes; this study aimed to examine the impacts of species, sex, and diet on thermal tolerance in mosquitoes. We found that Culex quinquefasciatus was inherently significantly more cold tolerant than Aedes aegypti, while Ae. aegypti had improved heat tolerance compared to Cx. quinquefasciatus. There were no differences in thermal tolerance between sexes within either species. We observed similar levels of cold tolerance between all diets tested, but observed decreased heat tolerance in mannitol-fed mosquitoes. Our results suggest that although dietary factors such as sugar alcohols and sugars may play a role in thermal tolerance in mosquitoes, there are likely physiological and genetic factors that can have a greater influence on the limits of thermal tolerance within a species.

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The current study involved exposing adult F0 Gulf killifish (Fundulus grandis) to Macondo-252 oil for 36 to 44 days and assessing the effects of this oiling on the swimming performance and morphology in two generations of progeny reared in clean water. Following exposure to oil, the F0 fish were used as broodstock to generate four lineages of F1 fish using a full-matrix mating design derived from the gametes of clean and oil-exposed parents. Later, the four lineages of F1 fish were used as broodstock to create an F2 generation of the same four lineages. We found few differences in embryonic outcome (% dead,% hatched, and% unhatched) in any of the four lineages of F1 and F2 fish. However, as adults, F1 and F2 fish derived from oil-exposed males from the F0 generation had significantly lower critical swimming speeds (Ucrit) than both the control and maternally oil-exposed lineages. Additionally, progeny of oil-exposed fish had altered body shape based on the statistical analysis of two-dimensional landmark-based geometric morphometrics. Fish from oil-exposed lineages showed increased body depth, altered spinal curvature, and changes in the upward angle of projection of the head. Both generations had a significant main effect of maternal and paternal oil exposure on shape; however, F0 paternal oil exposure explained more of the variance in shape across both generations relative to F0 maternal exposure. Our findings demonstrate that parental exposure to oil can impact the shape and aerobic swimming capacity of offspring for at least two generations after the original paternal oiling.

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The fungus Aspergillus flavus infects corn, peanut, and cottonseed, and contaminates seeds with acutely poisonous and carcinogenic aflatoxin. Aflatoxin contamination is a perennial threat in tropical and subtropical climates. Nonaflatoxin-producing isolates (atoxigenic) are deployed in fields to mitigate aflatoxin contamination. The biocontrol competitively excludes toxigenic A. flavus via direct replacement and thigmoregulated (touch) toxin inhibition mechanisms. To understand the broad-spectrum toxin inhibition, toxigenic isolates representing different mating types and sclerotia sizes were individually cocultured with different atoxigenic biocontrol isolates. To determine whether more inhibitory isolates had a competitive advantage to displace or touch inhibit toxigenic isolates, biomass accumulation rates were determined for each isolate. Finally, to determine whether atoxigenic isolates could inhibit aflatoxin production without touch, atoxigenic isolates were grown separated from a single toxigenic isolate by a membrane. Atoxigenic isolates 17, Af36, and K49 had superior abilities to inhibit toxin production. Small (<400 µm) sclerotial, Mat1-1 isolates were not as completely inhibited as others by most atoxigenic isolates. As expected for both direct replacement and touch inhibition, the fastest-growing atoxigenic isolates inhibited aflatoxin production the most, except for atoxigenic Af36 and K49. Aflatoxin production was inhibited when toxigenic and atoxigenic isolates were grown separately, especially by slow-growing atoxigenic Af36 and K49. Additionally, fungus-free filtrates from atoxigenic cultures inhibited aflatoxin production. Toxin production inhibition without direct contact revealed secretion of diffusible chemicals as an additional biocontrol mechanism. Biocontrol formulations should be improved by identifying isolates with broad-spectrum, high-inhibition capabilities and production of secreted inhibitory chemicals.

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Multiple comparisons tests (MCTs) include the statistical tests used to compare groups (treatments) often following a significant effect reported in one of many types of linear models. Due to a variety of data and statistical considerations, several dozen MCTs have been developed over the decades, with tests ranging from very similar to each other to very different from each other. Many scientific disciplines use MCTs, including >40,000 reports of their use in ecological journals in the last 60 years. Despite the ubiquity and utility of MCTs, several issues remain in terms of their correct use and reporting. In this study, we evaluated 17 different MCTs. We first reviewed the published literature for recommendations on their correct use. Second, we created a simulation that evaluated the performance of nine common MCTs. The tests examined in the simulation were those that often overlapped in usage, meaning the selection of the test based on fit to the data is not unique and that the simulations could inform the selection of one or more tests when a researcher has choices. Based on the literature review and recommendations: planned comparisons are overwhelmingly recommended over unplanned comparisons, for planned non-parametric comparisons the Mann-Whitney-Wilcoxon U test is recommended, Scheffé's S test is recommended for any linear combination of (unplanned) means, Tukey's HSD and the Bonferroni or the Dunn-Sidak tests are recommended for pairwise comparisons of groups, and that many other tests exist for particular types of data. All code and data used to generate this paper are available at: https://github.com/stevemidway/MultipleComparisons.

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Chemical dispersants are an important technology in the remediation of oil spills in the aquatic environment, facilitating degradation of crude oil and salinity is an important factor in dispersant effectiveness. The aim of the present study was to explore the role of salinity on the degradation chemistry of crude oil polycyclic aromatic hydrocarbons (PAHs) and acute toxicity of the water accommodated fraction (WAF) of the dispersant COREXIT 9500A and chemically dispersed crude oil on a common estuarine fish. Laboratory microcosms were designed at salinities of 4 parts per thousand (ppt), 12 ppt, or 18 ppt and spiked with crude oil, COREXIT 9500A, or a combined exposure to crude oil and COREXIT and allowed to biodegrade for 1 wk, 4 wk, and 16 wk. The WAF was harvested for analytical PAH analysis and acute toxicity testing in juvenile Fundulus grandis. Compared with undispersed oil, COREXIT exponentially increased the PAH concentrations in the WAF for up to 16 wk; hopane-normalized concentrations indicated that biodegradation was slowed for the first 4 wk. Dispersed crude oil and COREXIT were acutely toxic following 1 wk of biodegradation with no correlation between PAH concentrations and crude oil WAF mortality. Both dispersant and dispersant oil mixtures remained toxic for at least 4 wk at the lowest salinity tested, suggesting increased sensitivity or reduced biodegradation of toxic components in low-saline environments. At the lowest salinity, oil dispersed with COREXIT was more toxic than either the COREXIT alone or oil alone, even after 16 wk of biodegradation.

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Aspergillus flavus is considered a generalist-opportunistic pathogen, but studies are beginning to show that A. flavus populations have strains specific to various hosts. The research objective was to determine whether A. flavus soil populations consist of solely saprophytic strains and strains which can be facultatively parasitic on corn. A. flavus was isolated from both corn kernels and soil within 11 Louisiana fields. Sixteen vegetative compatibility groups (VCGs) were identified among 255 soil isolates. Only 6 of the 16 VCGs were identified in the 612 corn isolates and 88% of corn isolates were in two VCGs, whereas only 5% of soil isolates belonged to the same two VCGs. Isolates were characterized for aflatoxin B1 production and sclerotial size. A random subset of the isolates (99 from corn and 91 from soil) were further characterized for simple-sequence repeat (SSR) haplotype and mating type. SSR polymorphisms revealed 26 haplotypes in the corn isolates and 78 in the soil isolates, and only 1 haplotype was shared between soil and corn isolates. Corn and soil populations were highly significantly different for all variables. Differences between corn and soil populations indicate that some soil isolates are not found in corn and some isolates have become specialized to infect corn. Further understanding of A. flavus virulence is important for development of resistant hybrids and for better biological control against toxigenic A. flavus.

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