HZAM (Hybrid Zone with Assortative Mating) videos (August 2019 bioRxiv version and final published AmNat version)

This page contains simulation videos that may be of interest to readers of this paper:

Irwin, D.E. Assortative mating in hybrid zones is remarkably ineffective in promoting speciation. American Naturalist, published online May 4, 2020: https://doi.org/10.1086/708529

The earlier bioRxiv manuscript was:

Irwin, D.E. 2019. Assortative mating in hybrid zones is remarkably ineffective in promoting speciation. bioRxiv https://doi.org/10.1101/637678

Here is a simulation showing what happens when two populations come into contact, with strong assortative mating but no problems with hybrids (hybrids have high survival just like the parental forms): a complete continuum between the species develops:

Contact zone with strong (10x) assortative mating and no specified postzygotic isolation.

In contrast, here is a a simulation in which there is zero assortative mating, but hybrids have 10% lower fitness than “pure” individuals from the two populations. There is lots of hybridization at the start, but the width of the zone stays narrow:

Contact zone with 10% lower fitness of hybrids, and no assortative mating.

We can fit a cline (the blue line) to how the hybrid index (HI) depends on location, and define the width of the zone as being between HI=0.1 and HI=0.9. We can run the simulation for 1000 generations (with a frame every 5 generations), and see this line fluctuate but the width stays narrow:

Contact zone with 10% lower fitness of hybrids, and no assortative mating (with frames every 5 generations for 1000 generations)