Stickleback Case Study

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Stickleback Case Study Katherine Hale BIOL 112-02 2/14/23 1. What are the four mechanisms of genetic divergence ? What is a short definition of each? a. The four mechanisms of genetic divergence include mutation, which applies to any change in the DNA sequence of a cell , natural selection, the process of populations of living organisms adapt and change, the founder effect, and genetic drift . The founder effect is when a small group of individuals become isolated from a larger population, where the smaller group may establish a new population whose gene pool isn't reflective of the source population . Whereas genetic drift is the change in frequency of an existing gene variant in the population due to random chance. Part II– Interaction Between Benthic and Limnetic Sticklebacks 1. Define F1 and F2.Why are both crosses necessary (this what the definition of a species is)? a. F1 represents the children of the parents while the F2 represents the offspring of the F1 generation and are the grandchildren of the P generation. It is necessary to include both crosses because it allows us to see if the new hybrids can not only survive, but successfully reproduce with each other. 2. What can we conclude from the data in Table 1? a. We can conclude that the generations of hybrids can successfully reproduce with each other, which gives the indication that there is a good chance of the hybrids successfully creating their own species. 3. What can we conclude from the data in table 2? (i.e.Can they reproduce? What does this mean? Do they reproduce regularly?) a. When comparing the hybrids’ data to the benthic and limnetic sticklebacks’ numbers, it is clear over the three years the hybrids’ reproduction and survival rate have not yet become as dependable as the 2 other established species. However, the increase in their population between year 2 and 3 proves that they can in fact reproduce. 4. Are the sticklebacks physiologically different (give examples)? How do hybrids compare? a. It is evident that the physiology of the two sticklebacks are very different where they do not share one anatomical similarity out of the 7 categories that were measured. The benthic’s population have a significantly larger percent of having 2 dorsal spines and no pelvic girdle, while the Limnetic population have a higher average of lateral plates and gill rakers that are also superior in length compared
to the benthics. The hybrids’ morphology revealed that their anatomy is a median between the differing traits of benthic and limnetic sticklebacks. 5. What are two (2) reasons why hybrid numbers are so low in Paxton Lake? a. The hybrids’ low population in Paxton Lake could be a result of their morphological traits being an average of the benthic and limnetic’s genes instead of being passed down its parents anatomical benefits, which could make them less fit and decrease their chances of survival against predators. Another reason hybrid sticklebacks are rare is because sexual contact between limnetic and benthic sticklebacks is far more rare compared to intra-species mating within their seperate groups (i.e., limnetic with limnetic and benthic with benthic sticklebacks). 6. Given the data from Tables 1–3, which of the three possible outcomes (i.e., one species, two species, or speciating) best describes the interaction between benthic and limnetic sticklebacks? In other words, do they form one species, separate species, or are they in the process of speciation?Why? a. Given the data from all three tables, I believe that the benthic and limnetic sticklebacks are factually one species. I think this is the case because in table 1 it gives the survival rate for the F1 fertilized eggs and F2 hybrid fertilized eggs. Of the 659 F1 fertilized eggs, 626 of those eggs survived for a survival rate of 95%. Of the 525 F2 hybrids fertilized eggs, a total of 504 eggs survived for a survival rate of 96%. If the species was in the process of speciation, the survival rating for the F1 hybrids should be significantly lower and the F2 hybrids even lower than the F1 hybrids, if the F2's are even possible in the first place. In Table 3, its shown that the F2 hybrids also share almost half of the qualities and anatomy of both the benthic and limnetic sticklebacks, lending support that the limnetic and benthic sticklebacks are currently one species. However, based off of Table 2 where the hybrid sticklebacks account for approximately 1% of the population of each year for the three-year period, it can also be presumed that the two groups could begin the process of speciation, if they do not increase their frequency of reproduction with eachother.
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