Alright. Our example here says that below are three descriptions of hybrid zones. For each, read the description to the side of describing reinforcement, stability, or fusion in the hybrid zone. Write your answer on the line provided not all answers may be represented, and answers may be used more than once. So let's check it out.

The first one says that sea urchins are broadcast spawners, meaning they release sperm and eggs into the water to reproduce. Allopatric sea urchin species show no gametic reproductive isolation and can form hybrids in the lab. However, sympatric populations do show gametic isolation, and the sperm and egg from different species do not hybridize. So what does that sound like? Reinforcement, stability, or fusion?

Alright. Well, strong prezygotic barriers, that's the mark of reinforcement. Right? Where they are in sympatry, you have strong prezygotic barriers, making sure that these organisms don't waste their time mating with the wrong species. Where they're in allopatry, you don't have them, because you don't need them.

Then B says, Townsend and hermit warblers are closely related species found in Western North America. In areas of sympatry, hybrids regularly form, though they have lower fitness. It is thought that new adults move into the hybrid zone regularly from the parent populations, though gene flow out of the hybrid zone is much less common. Alright.

What do you think is going to happen there? Well, to me, that sounds like a stable hybrid zone. So I'm going to write stability here. Right? You have stability.

You have gene flow into the hybrid zone, but it says that new adults move into the hybrid zone regularly from the parent population, though gene flow out of the hybrid zone is much less common. So you're going to keep making hybrids, but there's not enough gene flow back into the parent populations to erase those species boundaries, a stable hybrid zone. Alright. Finally, C here says, on the Galapagos Islands, the small ground finch (we don't need to worry about the species) and the large ground finch show strong mating preference for members of the same species in sympatry, but not allopatry.

What do you think? Well, again, that has the hallmark of reinforcement. Right? Those sympatric populations show strong mating preferences for members of their own species, right? That's that behavioral isolation, but it doesn't happen in allopatry.

That's a clear sign of reinforcement. Alright. With that, practice after this. I'll see you there.