Herbivorous insects tend to be highly specialized in their use of host plants. Populations of gall wasp B. treatae inhabit two s
ister species of live oak, Quercus virginiana and Q. geminata, which geographically overlap in the southeastern United States. The habitat of each oak differs slightly, with Q. virginiana occurring in sites that are more moist, more nutrient rich, and have higher pH. Q. virginiana has larger, tougher leaves and earlier flowering times. How can conditions in the live oak habitats lead to speciation in gall wasps?
There would be natural variation in a population of gall wasps. This would mean that some members would be at an advantage in the first kind of live oak while others in the population would have traits that provide them an advantage in the other kind of live oak. Over time, the gall wasps would become even more specialized to living in the specific live oaks. This habitat isolation would build a reproductive barrier that would allow the two gall wasp populations to become more genetically different over time. At some point, the populations will become different enough that they can no longer interbreed. At this point, they would be considered different species.
