Many of us don’t think of the Galápagos as a place that is urbanized, but as we’ve discussed here on Life in the City previously, there is substantial human impact in the archipelago. An estimate from 2012 places the population size at 35,000 people — about 10 times the population just 4 decades earlier. Because researchers have been studying the evolutionary patterns of Darwin’s Finches for centuries, they are an exceptional system to study how urbanization influences evolution. If you’re unfamiliar with this group, Darwin’s Finches have evolved different beak sizes and shapes to feed on different foods. Two researchers at the Evolution 2019 meeting, Dr. Luis De Leon and Dr. Kiyoko Gotanda presented their recent work on the impacts of urbanization on Darwin’s Finches.
First, Dr. De Leon discussed how increased urbanization comes with an introduction of new anthropogenic foods to the Galápagos islands (a topic we discussed here recently). This introduction could weaken the selection that drives and maintains adaptive divergence. To investigate this question De Leon and colleagues conducted over 2,000 feeding trials in Darwin’s Finches. De Leon found a 24% overlap in diet trials conducted in non-urban areas and a 96% overlap in diet trials conducted at urban sites. Moreover, De Leon found that finch diet at urban sites is dominated by human foods. This means that finches at disturbed (urban) sites are no longer matching their morphological diet. De Leon left us with this bit to think about– Darwin wrote that species have been, “modified for different ends” but with current urbanization, species may be “modified for similar ends.”
You can watch Dr. De Leon’s full presentation here:
Later in the day, Dr. Gotonda discussed a cafeteria experiment with Darwin’s Finches. In this experiment trays of food (plastic Easter eggs filled with different food items and placed on a cardboard egg carton) were put outside. Trays were placed in three sites: one with no human presence, a beach with human presence but not permanent residents, and a town. Gotonda et al. found that at the site with no human presence finches ate all foods equally, but at the beach and town sites, finches preferred eating human foods — particularly chips, cookies, and rice. Next, researchers examined what tastes finches preferred: salty, sweet, bitter, oil, or neutral. Researchers found that finches at the town site preferred sweet foods. Because diet influences microbiome, researchers then examined the microbiome of finches among different sites using a “poop machine” or “craptraption”. Gotonda and colleagues found that small ground finches (Geospiza fuliginosa) have different microbiomes in areas with humans and human foods compared to areas without human food. The same is true for medium ground finches (Geospiza fortis). However, at sites with human foods, the microbiome of the two species is not similar.
Overall, this research is helping us understand the profound impacts that humans are having on species. If you want to learn more, you can read about the individual studies linked below.
De León, L. F., Sharpe, D. M. T., Gotanda, K. M., Raeymaekers, J. A. M., Chaves J. A., Hendry, A. P., Podos, J. (2018) Human foods erode niche segregation in Darwin’s finches. Evolutionary Applications
Knutie, S. A., Chaves, J.A., Gotanda, K. M. (2019) Human disturbances can influence the body mass and gut microbiota of Darwin’s finches. Molecular Ecology 28(9): 2441-2450
Featured photo: “Small Ground Finch (Geospiza fuliginosa)” by Victor W. Fazio III is licensed under CC BY-NC-SA 2.0
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