Resource-combining costs of being a diet generalist in the super-generalist protist predator Dictyostelium discoideum
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Abstract
Consumers lie on a continuum between diet specialization on few resources to being generalist feeders on many resources. Generalism has the clear advantage of having more resources to exploit, but the costs that limit generalism are less clear. We explore two understudied costs of generalism in a super-generalist amoeba predator, Dictyostelium discoideum , feeding on naturally co-occurring bacterial prey. Both involve costs of combining different prey. First, amoebas exhibit a reduction in growth rate when they switch from one species of prey bacteria to another, something we call resource-switching costs. These switching costs typically disappear within a day, indicating adjustment to new prey bacteria. Second, amoebas usually divide more slowly on mixtures of bacteria compared to on single bacteria, something we call resource-mixing costs. Both results support that idea that, although amoebas can consume a huge variety of prey, they must use partially different methods and thus must pay costs to handle multiple prey, either sequentially or simultaneously.
Significance Statement
Perhaps the most fundamental conflict in nature occurs when one organism consumes another. Diet generalists benefit from the advantage of eating many prey but then must deal with many prey defences. We explore costs associated with a broad diet in a protist microbial predator, Dictyostelium discoideum . These predators of bacteria show a delay in growth when switched from one bacteria to another, supporting the hypothesis that they must deploy different strategies. They also experience costs when grown on many bacteria at once, suggesting that the alternative strategies for consuming different prey are partly incompatible with each other. Our findings shed light on the nature of diet generalism and highlight the complexity of predation in the microbial world.
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Thus, it would be interesting to test if D. discoideum amoebas can avoid some concurrent costs by preferentially eating the most profitable prey bacteria first, but if they do, our data show that it is apparently not enough to fully overcome such cost
Interesting! Do you think this picky-eating theory could explain delayed growth? It takes longer to eat because they have to sort through the less-profitable prey to find their favorite meal?
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D. discoideum do not experience switching costs if they undergo spore formation before the prey switch
While not statistically significant as a whole, it does look like the Fg-Sm & Pv-At effects observed in Figure 3 are conserved after undergoing spore formation. Do you think certain bacterium might induce these genetic changes?
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10 OD600 bacterial suspension on starving agar
Were all 22 species of bacteria maintained in the same media? I could imagine different bacterial media components (even though low concentration) could impact Dicty's growth.
Similarly, do all 22 bacteria have similar doubling times? If Kp doubles 2x faster than Po, that could impact why amoeba double quicker on Kp than Po
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Discussion
There was a recent paper that showed differences in growth of a heterotrophic algae when fed different strains of the same genus! It would be interesting to see the variability of Dicty growth when fed different strains of the same species!
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We measured the growth rate of D. discoideum on 22 species of soil bacteria and the commonly used food bacterium K. pneumoniae.
Thank you for sharing this work as an open access preprint! It is a fun read and I learned a lot!
Each condition has 3 dots representing QS1, QS6, and QS9, correct? Are these strains maintained on K. pneumoniae in the lab, explaining their quickest doubling time on Kp?
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