IRCEB: Host-Pathogen Biology and the Global Decline of Amphibians

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9977063Collins et al. We propose an IRCEB in host-pathogen biology with a strong problem-solving focus designed to enhance collaboration and encourage pursuit of answers beyond the boundaries of traditional scientific disciplines. Host-pathogen interactions alternately fascinate and frustrate biologists. The fascination stems from the opportunities these systems offer as models for understanding at a basic level the complex mechanisms underlying organismal relationships. The frustration stems from not understanding these interactions sufficiently well to anticipate or react to epidemics or epizootics. Ecologists increasingly acknowledge a role for pathogens in population dynamics and in maintaining diverse communities and ecosystems. We have a poor understanding, however, of how pathogens alter host population dynamics, how pathogens infect hosts in a population, and how host and pathogen populations coevolve. In many populations, hosts and pathogens coexist and each shows regular increases and decreases in population size. At times, however, a pathogen nearly or completely decimates its host population. We propose testing the basic mechanisms underlying each of these patterns using amphibians as a model system. Most amphibian populations regularly fluctuate in numbers of individuals, but beginning about 1989 herpetologists became alarmed by reports that populations and even species were persistently declining, some to extinction. Extreme population fluctuations and declines are centered on a broad region of the Cordilleras of western North America from southern Saskatchewan south to Costa Rica and northern Panama, and the higher elevations of Australia from southeastern to north Queensland. Four main causes seem to be acting alone, sequentially, or synergistically: habitat destruction, exotic species, disease, and anthropogeneic environmental change due to toxic chemicals, UB radiation, or global climate change. Many regions with declines are conservation areas protected from exotic species and habitat destruction suggesting subtle, complex causes like environmental change or pathogens are at work. We have assembled an international research team to answer the question: Why are pathogens causing some amphibian populations to decline, even to extinction? The evidence suggests a pathogenic chytrid fungus causes populations to plummet, while another pathogen, an iridovirus causes amphibian populations to fluctuate. The proposed research will address the questions: How do pathogens influence host population dynamics? Are these newly-introduced amphibian pathogens, or has the virulence of historically benign amphibian associates changed? Have recent environmental changes altered amphibian-pathogen interactions? Except for some cases involving humans as hosts (e.g., cholera, malaria), few host-pathogen interactions have been dissected from molecular biology to population dynamics. Our team will do just that to advance basic host-pathogen biology with the goal of applying our findings to one of the most significant global biodiversity problems facing us today: Why are amphibian populations declining? Metaphorically, the declining amphibian problem is like a prism in reverse: instead of dispersing colors, it focuses research disciplines - ecology, evolution, organismal biology, genetics, pathology, and immunology - so that they no longer appear individually. Understanding the basic mechanisms of host-pathogen interactions is central to our proposal and essential for answering the question of why amphibians are declining. The point of this metaphor is that while a spectrum can be "divided" into its colors, the variation is continuous - "divisions" are artificial and at the origin they disappear. Amphibians are integral parts of ecosystems in ways that place them at this metaphorical core. Therefore, we need a diversity of disciplines and a diversity of investigators willing to collaborate on integrative research projects. The declining amphibian case in an exciting, but unfortunate, opportunity to explore the boundaries of host-pathogen biology, and the time is now to understand why amphibians are declining. The point of our IRCEB research program is to meld diverse disciplinary concepts, methods, and traditions in ways that advance our understanding of pathogens as a factor in amphibian declines, a key example of the general loss of biodiversity.