Founder-flush speciation in Drosophila pseudoobscura: a large-scale experiment

Abstract

A founder-flush-crash model of speciation has been proposed that may particularly apply to island and other colonizations. Forty-five experimental and 12 control Drosophila pseudoobscura populations were studied during seven successive founder-flush-crash cycles, or c50 generations. Sexual isolation tests yield significantly positive assortative mating in a few tests between pairs of experimental populations. Populations with fewer founders (N = 1 or 3) yield more significant instances of assortative mating than those with more founders (n = 5, 7, or 9), and this difference becomes statistically significant for pooled data. Only one of 15 population pairs tested three times (generations 25, 32, and 46) shows positive assortative mating in all three tests. No significant assortative mating occurs between control populations, including highly inbred ones. Although founder events may occasionally lead to the evolution of assortative mating and hence to speciation, results do not support the claim that the founder-flush-crash model identifies conditions very likely to result in speciation events. -from Authors