Infectious diseases can influence evolutionary mechanisms in a variety of ways, including extinction of host populations. While disease is rarely considered as a forcing agent in extinction, whether alone or in combination with co factors (e.g., climate change), it is nevertheless obvious from modern examples that disease can have extraordinary effects on the fitness of natural populations.
In this proposal it is contended that: (1) extinctions due to disease have occurred in the recent past (late Pleistocene); (2) these losses were prompted by genetically naive populations of animals encountering infectious diseases brought from elsewhere by migrating humans, their commensals, or synanthropics), which quickly emerged thereafter in these new hosts, causing catastrophic mortality; and (2) empirical evidence of pathogens is recoverable from late Pleistocene material, utilizing molecular ("ancient" DNA) and immunological approaches (thereby permitting realistic tests of the hypothesis).
The target extinction event for this work is the major series of losses that occurred in North America and northern Asia ca. 11,000 years ago. The principal target taxon is Mammuthus primigenius, the woolly mammoth, chosen because it is represented by abundant, high-quality fossils (including soft tissues). This taxon is also being heavily investigated by molecular methods for systematic and phylogenetic purposes in a number of labs, providing a good database for quality control of results. Other late Pleistocene taxa will also be utilized where feasible, as will remains other than bones (especially feces). The intent is to search for evidence of pathogenic entities (in particular, viruses) in well-preserved fossils collected by team members in the Taimyr Peninsula, Siberia, as well as other locales.
Hypotheses to be tested by relevant experiments are logically linked in a series of steps. Experiments may be grouped as follows:
Group 1 experiments are linked to the hypothesis that exogenous virus capsid proteins or host antibodies raised against virus infection can be detected immunochemically in tissues and feces of extinct species. Purpose of experiments is to use radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA), and immuno-PCR to detect DNA and RNA viruses.
Group 2 experiments are linked to the hypothesis that exogenous DNA viruses in fossil samples can be detected using ancient DNA techniques developed for single-copy nuclear DNA analysis. Purpose of experiments is to obtain sequence information on DNA viruses identified by RIA.
Group 3 experiments are linked to the hypothesis that mammoth populations may have suffered from reduced fitness (and therefore increased susceptibility to disease) as the result of genetic uniformity. Experiments are designed to analyze population genetics of geographically and temporally discrete mammoth samples, to look for evidence of genetic bottlenecking.
Any success in detecting and characterizing viral elements in fossil material will be groundbreaking, leading to the possibility of being able to empirically track evolutionary change in viruses at the gene level over periods of tends of thousands of years. Further, if the expected correlations between taxa, pathogens, and extinction times can be shown to be meaningful, this will have substantial impact on evolutionary biology, conservation biology, and virology. Dissemination of results through publications, symposia, and Web products is planned.