Migration pulsedness alters patterns of allele fixation and local adaptation in a mainland-island model

Geneflow across populations is a critical determinant of population genetic structure, divergence, and local adaptation. While evolutionary theory typically envisions geneflow as a continuous connection among populations, many processes make it fluctuating and intermittent. We analyze a mainland-island model where migration occurs as recurrent "pulses." We derive mathematical predictions regarding how the level of migration pulsedness affects the effective migration rate, for neutral and selected mainland alleles. We find that migration pulsedness can either decrease or increase geneflow, depending on the selection regime. Pulsedness increases geneflow for sufficiently (counter)selected alleles (s