Batrachochytrium salamandrivorans (Bsal) is an emerging invasive pathogen that is highly pathogenic to salamander species. Modeling infection dynamics in this system can facilitate proactive efforts to mitigate this pathogen's impact on north American species. Given its widespread distribution and high abundance, the eastern newt (Notophthalmus viridescens) has the potential to significantly influence Bsal epidemiology. We designed experiments to 1) estimate contact rates given different host densities and habitat structure and 2) estimate the probability of transmission from infected to susceptible individuals. Using parameter estimates from data generated during these experiments, we modeled infection and disease outcomes for a population of newts using a system of differential equations. We found that host contact rates were density-dependent, and that adding habitat structure reduced contacts. the probability of Bsal transmission given contact between newts was very high (>90%) even at early stages of infection. our simulations show rapid transmission of Bsal among individuals following pathogen introduction, with infection prevalence exceeding 90% within one month and >80% mortality of newts in three months. Estimates of basic reproductive rate (R 0) of Bsal for eastern newts were 1.9 and 3.2 for complex and simple habitats, respectively. Although reducing host density and increasing habitat complexity might decrease transmission, these management strategies may be ineffective at stopping Bsal invasion in eastern newt populations due to this species' hypersusceptibility. Across a variety of taxa, disease has been implicated as a major contributor to population-and species-level declines 1-6. Epidemiological modeling can facilitate disease response and management by elucidating host-pathogen interactions and identifying strategies that could reduce the severity of outbreaks in wild populations 7-9. Ideally, evaluating disease management strategies and modeling possible outcomes should occur prior to pathogen invasion, because the likelihood for disease control is greater and the cost of response is less 8,10-12. Conversely, reactive or delayed responses to disease outbreaks can result in significant biodiversity loss and economic impact, as demonstrated by the unexpected emergence of Batrachochytrium dendrobatids (Bd) 6,13,14 and Pseudogymnoascus destructans (the causative agent of White Nose syndrome) 13,15. The newly emergent fungal pathogen Batrachochytrium salamandrivorans (Bsal) provides a unique opportunity to evaluate possible management strategies, especially in areas where it has yet to emerge. Bsal is rapidly spreading in Europe, where it is believed to have been introduced from Asia via the pet trade 16,17. In areas where Bsal has emerged, populations of fire salamanders (Salamandra salamandra) have declined substantially 18. Preventing and mitigating Bsal outbreaks is described as one of the greatest current priorities for wildlife conservation 19. Bsal appears to have a high invasion probability ...

The deterioration in functions with age, a phenomenon termed senescence, is prevalent across the tree of life (Jones et al., 2014). Patterns of reproductive senescence vary widely among species with contrasting life histories, but, in general, life histories are considered to have evolved to optimize reproductive success given life expectancy (Williams, 1966; Gadgil and Bossert, 1970; Charnov et al., 2007) and the expected (i.e., seasonal and/or stochastic) progression of environments (Giesel, 1976). The survival-reproduction tradeoff is further complicated in hermaphroditic plants by the balance of male and female roles within individual flowers, as well as the possibility of self-fertilization. Sex allocation theory posits that predominantly self-fertilizing species (hereafter selfers) will allocate a greater proportion of reproductive resources toward fertilized ovule development to produce seeds, while outcrossing species (hereafter outcrossers) will divert more towards pollen production and delivery (Lloyd, 1987; Parker et al., 1995). Underlying both life history and sex allocation theories is the premise that resources are limited, and allocation to one function results in tradeoffs that incur fitness costs (Day and Aarssen, 1997). At the core of the differences between selfing and outcrossing mating systems is the form of pollen delivery. In particular, outcrossers often rely on visitation from animal vectors for pollen

Controlled experiments are one approach to understanding the pathogenicity of etiologic agents to susceptible hosts. The recently discovered fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has resulted in a surge of experimental investigations because of its potential to impact global salamander biodiversity. However, variation in experimental methodologies could thwart knowledge advancement by introducing confounding factors that make comparisons difficult among studies. Thus, our objective was to evaluate if variation in experimental methods changed inferences made on the pathogenicity of Bsal. We tested whether passage duration of Bsal culture, exposure method of the host to Bsal (water bath vs. skin inoculation), Bsal culturing method (liquid vs. plated), host husbandry conditions (aquatic vs. terrestrial), and skin swabbing frequency influenced diseased-induced mortality in a susceptible host species, the eastern newt (Notophthalmus viridescens). We found that disease-induced mortality was faster for eastern newts when exposed to a low passage isolate, when newts were housed in terrestrial environments, and if exposure to zoospores occurred via water bath. We did not detect differences in disease-induced mortality between culturing methods or swabbing frequencies. Our results illustrate the need to standardize methods among Bsal experiments. We provide suggestions for future Bsal experiments in the context of hypothesis testing and discuss the ecological implications of our results.

Hybridization between organisms from evolutionarily distinct lineages can have profound consequences on organism ecology, with cascading effects on fitness and evolution. Most studies of hybrid organisms have focused on organismal traits, for example various aspects of morphology and physiology. However, with the recent emergence of holobiont theory, there has been growing interest in understanding how hybridization impacts and is impacted by host-associated microbiomes. Better understanding of the interplay between host hybridization and host-associated microbiomes has the potential to provide insight into both the roles of host-associated microbiomes as dictators of host performance as well as the fundamental rules governing host-associated microbiome assembly. Unfortunately, there is a current lack of frameworks for understanding the structure of host-associated microbiomes of hybrid organisms. In this paper, we develop four conceptual models describing possible relationships between the host-associated microbiomes of hybrids and their progenitor or parent taxa. We then integrate these models into a quantitative 4H index and present a new R package for calculation, visualization, and analysis of this index. Finally, we demonstrate how the 4H index can be used to compare hybrid microbiomes across disparate plant and animal systems.