18
1. Since the beetles’ environments are different colors, there will be different phenotypes that are considered “most fit.” For example, on the side with dark soil and not much grass, those beetles that happen to have a darker exoskeleton would be more camouflaged and have a better chance at surviving (not being eaten). This would lead to a change in the gene pool to have a higher percentage of dark-colored beetles. The opposite would occur on the side with more grass coverage; the beetle population would evolve to have a higher percentage of green-colored exoskeletons. If these two populations of beetles are no longer able to interbreed because brown beetles only choose to mate with other brown beetles (and green beetles mate only with green beetles), speciation has occurred!
2. One species of flower can be fertilized by another species of flower, but once the egg and sperm fuse, their differing chromosome numbers prevents the formation of a viable zygote. This is an example of offspring viability, a type of post-zygotic barrier that prevents the production of offspring between two different species.
3. About 200 years ago, an ancestral population of flies laid their eggs on tree fruits called hawthorns. Once domestic apple trees were introduced, some flies in the population chose to lay their eggs on apples, instead. The maggots that developed in the hawthorn fruit grew into adult flies who preferred to mate with other hawthorn-reared flies; maggots from apples developed into flies who preferred to mate with other apple-grown flies. This is an example of behavioral isolation, a type of pre-zygotic barrier that prevents the production of offspring between two different species.
4. Both terms refer to a genetic change in a species over time. Microevolution focuses on a change occurring in the gene pool of a specific species, whereas macroevolution looks at the bigger picture of how different species arise from an ancestral species (due to changes in their gene pools).
5. In order for speciation to occur, there needs to be some sort of barrier that divides the current population’s gene pool, thus interrupting the gene flow between the two resulting groups. Next, the isolated gene pools need to change/evolve in a way that renders them unable to interbreed if brought back together.
6. One species of field cricket mates in the spring, whereas a second species of field cricket mates in the fall. This is an example of temporal isolation, a type of pre-zygotic barrier that prevents the production of offspring between two different species.
7. c. Offspring viability means that even though fertilization did occur and an offspring was produced, the offspring was not healthy enough to survive.