Fire effects on plant reproductive fitness vary among individuals, reflecting pollination-dependent mechanisms.

PREMISE: Fire induces flowering in many plant species worldwide, potentially improving reproductive fitness via greater availability of resources, as evident by flowering effort, and improved pollination outcomes, as evident by seed set. Postfire increases in flowering synchrony, and thus mating opportunities, may improve pollination. However, few studies evaluate fire effects on multiple components of fitness. Consequently, the magnitude and mechanism of fire effects on reproductive fitness remain unclear. METHODS: Over multiple years and prescribed burns in a prairie preserve, we counted flowering stems, flowers, fruits, and seeds of three prairie perennials, Echinacea angustifolia, Liatris aspera, and Solidago speciosa. We used aster life-history models to assess how fire and mating opportunities influenced annual maternal fitness and its components in individual plants. RESULTS: In Echinacea and Liatris, but not in Solidago, fire increased head counts, and both fire and mating opportunities increased maternal fitness. Burned Echinacea and Liatris plants with many flower heads produced many seeds despite low seed set (fertilization rates). In contrast, plants with an average number of flower heads had high seed set and produced many seeds only when mating opportunities were abundant. CONCLUSIONS: Fire increased annual reproductive fitness via resource- and pollination-dependent mechanisms in Echinacea and Liatris but did not affect Solidago fitness. The consistent relationship between synchrony and seed set implies that temporal mating opportunities play an important role in pollination. While fire promotes flowering in many plant species, our results reveal that even closely related species exhibit differential responses to fire, which could impact the broader plant community.

Randomization for the susceptibility effect of an infectious disease intervention.

Randomized trials of infectious disease interventions, such as vaccines, often focus on groups of connected or potentially interacting individuals. When the pathogen of interest is transmissible between study subjects, interference may occur: individual infection outcomes may depend on treatments received by others. Epidemiologists have defined the primary parameter of interest-called the "susceptibility effect"-as a contrast in infection risk under treatment versus no treatment, while holding exposure to infectiousness constant. A related quantity-the "direct effect"-is defined as an unconditional contrast between the infection risk under treatment versus no treatment. The purpose of this paper is to show that under a widely recommended randomization design, the direct effect may fail to recover the sign of the true susceptibility effect of the intervention in a randomized trial when outcomes are contagious. The analytical approach uses structural features of infectious disease transmission to define the susceptibility effect. A new probabilistic coupling argument reveals stochastic dominance relations between potential infection outcomes under different treatment allocations. The results suggest that estimating the direct effect under randomization may provide misleading conclusions about the effect of an intervention-such as a vaccine-when outcomes are contagious. Investigators who estimate the direct effect may wrongly conclude an intervention that protects treated individuals from infection is harmful, or that a harmful treatment is beneficial.

Do Interactions among Microbial Symbionts Cause Selection for Greater Pathogen Virulence?

AbstractThe ecological and evolutionary consequences of microbiome treatments aimed at protecting plants and animals against infectious disease are not well understood, even as such biological control measures become more common in agriculture and medicine. Notably, we lack information on the impacts of symbionts on pathogen fitness with which to project the consequences of competition for the evolution of virulence. To address this gap, we estimated fitness consequences for a common plant pathogen, Ustilago maydis, over differing virulence levels and when the host plant (Zea mays) is coinfected with a defensive symbiont (Fusarium verticillioides) and compared these fitness estimates to those obtained when the symbiont is absent. Here, virulence is measured as the reduction in the growth of the host caused by pathogen infection. Results of aster statistical models demonstrate that the defensive symbiont most negatively affects pathogen infection and that these effects propagate through subsequent stages of disease development to cause lower pathogen fitness across all virulence levels. Moreover, the virulence level at which pathogen fitness is maximal is higher in the presence of the defensive symbiont than in its absence. Thus, as expected from theory for multiple parasites, competition from the defensive symbiont may cause selection for increased pathogen virulence. More broadly, we consider that the evolutionary impacts of interactions between pathogens and microbial symbionts will depend critically on biological context and environment and that interactions among diverse microbial symbionts in spatially heterogeneous communities contribute to the maintenance of the highly diverse symbiotic functions observed in these communities.

Incidence of and risk factors for major complications or death in dogs undergoing cytoreductive surgery for treatment of suspected primary intracranial masses.

OBJECTIVE To determine incidence of and risk factors for major complications occurring in dogs within 30 days after cytoreductive surgery performed by a single pair of surgeons for treatment of suspected primary intracranial masses. DESIGN Retrospective cohort study. ANIMALS 160 client-owned dogs that underwent cytoreductive surgery for treatment of suspected primary intracranial masses between January 2009 and December 2015 at a veterinary teaching hospital. PROCEDURES Medical records were retrospectively reviewed for complications occurring within 30 days after surgery. Data (eg, signalment, clinical signs, previous treatments, preoperative neurologic examination findings, neuroanatomical location, time from onset of clinical signs to surgery, surgical approach, and histopathologic diagnosis) were analyzed for associations with death and with development of major complications other than death. RESULTS 21 (13.1%) dogs died (11 during hospitalization and 10 after discharge) and 30 (18.8%) developed major complications other than death during the first 30 days after surgery. Dogs with abnormal preoperative neurologic examination findings were more likely to develop complications or die. Dogs undergoing a suboccipital approach were more likely to die. The most common postoperative complications other than death were seizures (n = 18 [11.3%]), worsening of neurologic status (6 [3.8%]), and aspiration pneumonia (6 [3.8%]). CONCLUSIONS AND CLINICAL RELEVANCE Results of the present study provided valuable information on predisposing factors, odds of major complications or death, and incidences of major complications or death in dogs during the first 30 days after undergoing cytoreductive surgery for treatment of suspected primary intracranial masses. Careful case selection may help improve outcomes and minimize complications.

Central Limit Theorems under additive deformations.

Additive deformations of statistical systems arise in various areas of physics. Classical central limit theory is then no longer applicable, even when standard independence assumptions are preserved. This paper investigates ways in which deformed algebraic operations lead to distinctive central limit theory. We establish some general central limit results that are applicable to a range of examples arising in nonextensive statistical mechanics, including the addition of momenta and velocities via Kaniadakis addition, and Tsallis addition. We also investigate extensions to random additive deformations, and find evidence (based on simulation studies) for a universal limit specific to each statistical system.

Poly(ADP-ribosyl)ation of Methyl CpG Binding Domain Protein 2 Regulates Chromatin Structure.

The epigenetic information encoded in the genomic DNA methylation pattern is translated by methylcytosine binding proteins like MeCP2 into chromatin topology and structure and gene activity states. We have shown previously that the MeCP2 level increases during differentiation and that it causes large-scale chromatin reorganization, which is disturbed by MeCP2 Rett syndrome mutations. Phosphorylation and other posttranslational modifications of MeCP2 have been described recently to modulate its function. Here we show poly(ADP-ribosyl)ation of endogenous MeCP2 in mouse brain tissue. Consequently, we found that MeCP2 induced aggregation of pericentric heterochromatin and that its chromatin accumulation was enhanced in poly(ADP-ribose) polymerase (PARP) 1(-/-) compared with wild-type cells. We mapped the poly(ADP-ribosyl)ation domains and engineered MeCP2 mutation constructs to further analyze potential effects on DNA binding affinity and large-scale chromatin remodeling. Single or double deletion of the poly(ADP-ribosyl)ated regions and PARP inhibition increased the heterochromatin clustering ability of MeCP2. Increased chromatin clustering may reflect increased binding affinity. In agreement with this hypothesis, we found that PARP-1 deficiency significantly increased the chromatin binding affinity of MeCP2 in vivo. These data provide novel mechanistic insights into the regulation of MeCP2-mediated, higher-order chromatin architecture and suggest therapeutic opportunities to manipulate MeCP2 function.

An integrated analysis of phenotypic selection on insect body size and development time.

Most studies of phenotypic selection do not estimate selection or fitness surfaces for multiple components of fitness within a unified statistical framework. This makes it difficult or impossible to assess how selection operates on traits through variation in multiple components of fitness. We describe a new generation of aster models that can evaluate phenotypic selection by accounting for timing of life-history transitions and their effect on population growth rate, in addition to survival and reproductive output. We use this approach to estimate selection on body size and development time for a field population of the herbivorous insect, Manduca sexta (Lepidoptera: Sphingidae). Estimated fitness surfaces revealed strong and significant directional selection favoring both larger adult size (via effects on egg counts) and more rapid rates of early larval development (via effects on larval survival). Incorporating the timing of reproduction and its influence on population growth rate into the analysis resulted in larger values for size in early larval development at which fitness is maximized, and weaker selection on size in early larval development. These results illustrate how the interplay of different components of fitness can influence selection on size and development time. This integrated modeling framework can be readily applied to studies of phenotypic selection via multiple fitness components in other systems.