Abstract
The ability of the site-frequency spectrum (SFS) to reflect the particularities of gene genealogies exhibiting multiple mergers of ancestral lines as opposed to those obtained in the presence of exponential population growth is our focus. An excess of singletons is a well-known characteristic of both population growth and multiple mergers. Other aspects of the SFS, in particular the weight of the right tail, are, however, affected in specific ways by the two model classes. Using minimum-distance statistics, and an approximate likelihood method, our estimates of statistical power indicate that exponential growth can indeed be distinguished from multiple merger coalescents, even for moderate sample size, if the number of segregating sites is high enough. Additionally, we use a normalised version of the SFS as a summary statistic in an approximate bayesian computation (ABC) approach to distinguish multiple mergers from exponential population growth. The ABC approach gives further positive evidence as to the general eligibility of the SFS to distinguish between the different histories, but also reveals that suitable weighing of parts of the SFS can improve the distinction ability. The important issue of the difference in timescales between different coalescent processes (and their implications for the scaling of mutation parameters) is also discussed.
