Why was the rainy season not an ideal good time to study the finches eating habits
Author’s note: Are Darwin’s finches “a particularly compelling example of speciation” as well as “evolution in action”? In a series of posts, I offer some notes on the question of whether macroevolution is happening on the Galápagos Islands. Please find the full series here. Show It may perhaps sound a bit confusing and contradictory when we read (Lamichhaney et al. in Nature 2015, referred to in my last post) that, “After a year of drought the finches with slightly larger beaks survived earlier than those with smaller beaks,” and also: “When the weather is dry, bigger-beaked birds do better. When the rain returns, smaller-beaked birds return to previous levels,” etc., and that during the time of the drought: “the researchers found that the large-beak HMGA2 variant was more common in birds that starved to death, while the small-beak variant was more common in birds that survived” (emphasis added). Solving the RiddleThe solution to the riddle? First phase (for the Wikipedia article, see here):
Second phase (for the Wikipedia article that is the source for this and subsequent quotations, see here):
Third phase:
Events Repeated?Now you would expect that the events that happened in 1977 would be repeated, namely:
But far from it. Instead, the following was observed:
Note the SubjunctiveWhy? The authors offer the following selectionist explanation, which is nevertheless uncertain. Note the repeated use of the subjunctive:
So, the situation concerning natural selection is not as simple as usually presented in the textbooks or in the later deleted comment of the National Academy of Sciences, which I discussed in the first two posts in this series. Rather, there are obviously important open questions yet to be solved, including the possible (not even mentioned above) effects of hybridization between Geospiza magnirostris and G. fortis. Nevertheless, even if the competition hypothesis between these two species were true, it would change the “Sisyphean evolution of Darwin’s finches” only with regard to its length and the number of its steps to fulfill the Sisyphean cycle. The more extensive but misleading claim of Peter and Rosemary Grant is that “selection oscillates in a direction.” Even if this doubtful assertion were true, it would ultimately be irrelevant for the origin of primary species and higher systematic categories. A sieve (natural selection), after all, cannot create new grains. Next, “Island Evolution of Species: Typogenesis, Typostasis or Typolysis?” Editor’s note: This article was updated on November 30, 2020. What happened to the finches during the drought?Because the drought reduced the number of seeds and finches with bigger beaks were able to eat the larger and harder seeds so more of them survived.
Why was Daphne Major an ideal place to study finches?Daphne Major serves as an ideal site for research because the finches have few predators or competitors. (The only other finch on the island is the cactus finch.) The major factor influencing survival of the medium ground finch is the weather, and thus the availability of food.
How did the changes in environment affect the finches?The Grants found that the offspring of the birds that survived the 1977 drought tended to be larger, with bigger beaks. So the adaptation to a changed environment led to a larger-beaked finch population in the following generation.
How did the 1977 drought affect the finches?A major drought hit the island in 1977, and 85% of the birds died. Having big beak raised the odds of a bird surviving, because it meant the animal could crack the hard spiked seeds. The Grants discovered that within a few years the population of finches the recovered.
|