Population of origin and environment interact to determine oomycete infections in spotted salamander populations

Ecosystem effects of intraspecific variation in a colour polymorphic amphibian

An emerging consensus suggests that evolved intraspecific variation can be ecologically important. However, evidence that evolved trait variation within vertebrates can influence fundamental ecosystem-level processes remains sparse. In this study, we sought to assess the potential for evolved variation in the spotted salamander (Ambystoma maculatum) to affect aquatic ecosystem properties. Spotted salamanders exhibit a conspicuous polymorphism in the colour of jelly encasing their eggs-some females produce clear jelly, while others produce white jelly. Although the functional significance of jelly colour variation remains largely speculative, evidence for differences in fecundity and the morphology of larvae suggests that the colour morphs might differ in the strength or identity of ecological effects. Here, we assessed the potential for frequency variation in spotted salamander colour morphs to influence fundamental physiochemical and ecosystem properties-dissolved organic carbon, conductivity, acidity and primary production-with a mesocosm experiment. By manipulating colour morph frequency across a range of larval densities, we were able to demonstrate that larva density and colour morph variation were ecologically relevant: population density reduced dissolved organic carbon and increased primary production while mesocosms stocked with white morph larvae tended to have higher dissolved organic carbon and conductivity. Thus, while an adaptive significance of jelly coloration remains hypothetical, our results show that colour morphs differentially influence key ecosystem properties-dissolved organic carbon and conductivity.

Saprolegniosis in Amphibians: An Integrated Overview of a Fluffy Killer Disease

Amphibians constitute the class of vertebrates with the highest proportion of threatened species, with infectious diseases being considered among the greatest causes for their worldwide decline. Aquatic oomycetes, known as “water molds,” are fungus-like microorganisms that are ubiquitous in freshwater ecosystems and are capable of causing disease in a broad range of amphibian hosts. Various species of Achlya sp., Leptolegnia sp., Aphanomyces sp., and mainly, Saprolegnia sp., are responsible for mass die-offs in the early developmental stages of a wide range of amphibian populations through a disease known as saprolegniosis, aka, molding or a “Saprolegnia-like infection.” In this context, the main objective of the present review was to bring together updated information about saprolegniosis in amphibians to integrate existing knowledge, identify current knowledge gaps, and suggest future directions within the saprolegniosis–amphibian research field. Based on the available literature and data, an integrated and critical interpretation of the results is discussed. Furthermore, the occurrence of saprolegniosis in natural and laboratory contexts and the factors that influence both pathogen incidence and host susceptibility are also addressed. The focus of this work was the species Saprolegnia sp., due to its ecological importance on amphibian population dynamics and due to the fact that this is the most reported genera to be associated with saprolegniosis in amphibians. In addition, integrated emerging therapies, and their potential application to treat saprolegniosis in amphibians, were evaluated, and future actions are suggested.

Balancing selection and drift in a polymorphic salamander metapopulation

Understanding how genetic variation is maintained in a metapopulation is a longstanding problem in evolutionary biology. Historical resurveys of polymorphisms have offered efficient insights about evolutionary mechanisms, but are often conducted on single, large populations, neglecting the more comprehensive view afforded by considering all populations in a metapopulation. Here, we resurveyed a metapopulation of spotted salamanders (Ambystoma maculatum) to understand the evolutionary drivers of frequency variation in an egg mass colour polymorphism. We found that this metapopulation was demographically, phenotypically and environmentally stable over the last three decades. However, further analysis revealed evidence for two modes of evolution in this metapopulation-genetic drift and balancing selection. Although we cannot identify the balancing mechanism from these data, our findings present a clear view of contemporary evolution in colour morph frequency and demonstrate the importance of metapopulation-scale studies for capturing a broad range of evolutionary dynamics.

Leptolegnia chapmanii como alternativa biológica para el control de Aedes aegypti

Leptolegnia chapmanii is a facultative pathogen of many species of mosquitoes, among which species of the genus Aedes, Culex and Anopheles stand out for their medical and sanitary importance. The potential of L. chapmanii as an alternative to control lies in its virulence, pathogenicity and specificity against the larval stages of mosquitoes, and because of its harmlessness to non-target species such as fish and amphibians, among others. The natural presence of L. chapmanii had been reported in Argentina, Brazil and the United States. Its presence is possible in other countries throughout the American continent. The development of protocols to produce, formulate, store and apply products based on this microorganism is one of the objectives proposed for the group of Entomopathogenic Fungi at the Centro de Estudios Parasitológicos y de Vectores, Universidad Nacional de La Plata. The efficacy of L. chapmanii as controller is affected by external factors such as temperature, pH, salinity and radiation among others. The process of transfer from the research centers to industry implies many phases. In this way, our project with L. chapmanii is in an initial phase, where we are working on a laboratory scale in proof of concept. We hope to begin soon with the efficacy, efficiency, stability and ecotoxicological safety tests, at the laboratory, semi-field and field scale.

Persistence of an egg mass polymorphism in Ambystoma maculatum: differential performance under high and low nutrients

Polymorphisms play critical roles in allowing organisms to adapt to novel environments while enabling ecological speciation under divergent selection. Ambystoma maculatum, the spotted salamander, exhibits a unique polymorphism in the structure and appearance of its egg masses with two common morphs, white and clear. Amphibian egg jelly layers mediate interactions between embryos and the environment and are more responsive to ecological pressures of natural selection than other egg coat components. The A. maculatum egg mass polymorphism was hypothesized to be adaptive with regard to varying dissolved nutrient levels in ponds. We conducted two mesocosm experiments, collected field data, and constructed a population projection model to determine how dissolved nutrient levels affect embryonic and larval development and relate to the distribution of the morphs in natural ponds. We found that upon hatching there was an interaction between nutrient level and egg mass morph wherein individuals from white morphs were larger in low nutrient habitats. This interaction persisted throughout the larval stage, and along with the higher abundance of white morphs in ponds with low conductivity, we demonstrate that the white morph is advantageous in low nutrient environments. Our findings provide evidence for the role of environmental heterogeneity in enabling the persistence of a structural egg mass polymorphism, with maintenance occurring across multiple scales and persistence across its range. This indicates that polymorphisms can maximize performance in heterogeneous environments, while persisting over long timescales without leading to sympatric speciation.

Refugia and connectivity sustain amphibian metapopulations afflicted by disease

Metapopulation persistence in fragmented landscapes depends on habitat patches that can support resilient local populations and sufficient connectivity between patches. Yet epidemiological theory for metapopulations has largely overlooked the capacity of particular patches to act as refuges from disease, and has suggested that connectivity can undermine persistence. Here, we show that relatively warm and saline wetlands are environmental refuges from chytridiomycosis for an endangered Australian frog, and act jointly with connectivity to sustain frog metapopulations. We coupled models of microclimate and infection probability to map chytrid prevalence, and demonstrate a strong negative relationship between chytrid prevalence and the persistence of frog populations. Simulations confirm that frog metapopulations are likely to go extinct when they lack environmental refuges from disease and lose connectivity between patches. This study demonstrates that environmental heterogeneity can mediate host-pathogen interactions in fragmented landscapes, and provides evidence that connectivity principally supports host metapopulations afflicted by facultative pathogens.

The evolution of foraging rate across local and geographic gradients in predation risk and competition

Multiple theories predict the evolution of foraging rates in response to environmental variation in predation risk, intraspecific competition, time constraints, and temperature. We tested six hypotheses for the evolution of foraging rate in 24 spotted salamander (Ambystoma maculatum) populations from three latitudinally divergent sites using structural equation models derived from theory and applied to our system. We raised salamander larvae in a common-garden experiment and then assayed foraging rate under controlled conditions. Gape-limited predation risk from marbled salamanders solely explained foraging rate variation among populations at the southern site, which was dominated by this form of selection. However, at the middle and northern sites, populations evolved different foraging rates depending on their unique responses to local intraspecific density. The coupling of gape-limited predation risk from marbled salamanders and high intraspecific density at the middle site jointly contributed to selection for rapid foraging rate. At the northernmost site, intraspecific density alone explained 97% of the interpopulation variation in foraging rate. These results suggest that foraging rate has evolved multiple times in response to varying contributions from predation risk and intraspecific competition. Predation risk often varies along environmental gradients, and, thus, organisms might often shift evolutionary responses from minimizing predation risk to maximizing intraspecific competitive performance.