Demographic inference reveals African and European admixture in the North American Drosophila melanogaster population

Abstract

Drosophila melanogaster spread from sub-Saharan Africa to the rest of the world colonizing new environments. Here, we modeled the joint demography of African (Zimbabwe), European (The Netherlands), and North American (North Carolina) populations using an approximate Bayesian computation (ABC) approach. By testing different models (including scenarios with continuous migration), we found that admixture between Africa and Europe most likely generated the North American population, with an estimated proportion of African ancestry of 15%. We also revisited the demography of the ancestral population (Africa) and found-in contrast to previous work-that a bottleneck fits the history of the population of Zimbabwe better than expansion. Finally, we compared the site-frequency spectrum of the ancestral population to analytical predictions under the estimated bottleneck model.

Figure 1

Three-population models. Numbers in parentheses are the posterior probabilities of each model. The symbols are explained in Table 3.

Figure 2

Observed (solid) and predicted (shaded) site-frequency spectrum of the African population. To calculate the frequency classes Equation 4 was used.

Figure 3

Predicted summary statistics under models A, B, and C for the North American population based on the rejection method. The horizontal dashed line represents the observed value.

Figure 4

Probability density of the proportion of European admixture based on the regression method (solid line) and rejection method (dashed line). The horizontal dotted line represents the uniform prior distribution.