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Evolutionary Biology
Cooperative coevolution
| Question | Answer |
|---|---|
| Social behaviours | Exchanges take place between an actor and a recipient and can have either positive or negative effects on the two parties |
| Social behaviours | In predatory/parasitic interactions, the actor (predator/parasite) gains fitness and the recipient (prey/host) loses fitness (because it is killed or made ill) |
| Competitive behaviours | The actor (competitor) loses fitness and the recipient (also competitor) loses fitness (because both harm each other) |
| Mutualistic behaviours | The actor (mutualist) gains fitness and the recipient (also mutualist) gains fitness (because both help each other) |
| Altruistic behaviours | The actor (altruist) loses fitness and the recipient (no special name) gains fitness (because the altruist helps the recipient at a cost to the altruist) |
| Altruism | • This is a behaviour that increases another individual’s fitness at a cost to one’s own fitness • On its own, altruism should not evolve because altruistic individuals lower their own fitness |
| Alarm calls | Reduces mortality risk for others + Increases mortality risk for self - |
| Nest helpers | Increases fecundity for others + Decreases fecundity for self - |
| Social insects | Increases fecundity for others + Zero fecundity for self - |
| Altruism should not evolve. But altruistic behaviours have evolved…how? | Short answer: altruistic behaviours only look altruistic (+/-). In reality, altruistic behaviours are mutualistic (+/+) |
| Kin selection | – natural selection can favour altruistic behaviour between kin e.g. Florida scrub jay |
| Reciprocity | – “You scratch my back, I’ll scratch yours” |
| Nest helping increases fecundity for parents + | Nest helping increase fitness for self through (1) additional siblings, (2) practice rearing offspring, and (3) increased probability of inheriting parents’ territory + |
| Allogrooming reduces parasite load for others + | Allogrooming reduces parasite load for self (when reciprocated in the future) + Requires memory and individual recognition “I will help those who have helped me (or others) before” |
| Mutualism | • Two different species: each species incurs a cost to benefit the other species • Often with animal/plant on one side and a microorganism on the other (bacteria, virus, fungi) |
| ie. Bobtail squid | • Squid provides food and housing (at a cost) to Vibrio fischeri bacteria • Bacteria glow (at a cost) • The glow lets the squid counter-illuminate the moon shadow, to avoid predation |
| ie. Upside-down jellyfish | • Jellyfish provides housing to algae • Algae give up some of their photosynthetic product to the jellyfish |
| Mutualism - cheating | • Imagine you have two kinds of individual on one side of a mutualism (helpers and cheaters) • The helper will have a lower fitness to the cheater, and the cheater genotype will go to fixation |
| Mutualism - cheating | • Kin selection cannot select for mutualism between different species • Reciprocity cannot select for mutualism when there is no individual recognition and memory |
| Trophic mutualism | • Partners specialised in obtaining energy and nutrients • E.g. Rhizobium and plant roots that form nitrogen fixing root nodules in exchange for sugars • Cellulose digesting bacteria in the rumens of cows |
| Defensive mutualism | Involve species that receive food or shelter from their partner in return for a defensive function • E.g. ants and antplants |
| Dispersal mutualism | • Involve animals that transport either: • Pollen in return for nectar • Seed in return for a fruit reward |
| Leafcutter ant-fungus mutualism | • Ants cut leaves and feed leaf fragments to a specialised fungus • Fungus digests the leaves and makes food to feed ant larvae - essentially the ants are fungus farmers |
| Leafcutter ant-fungus mutualism | • Different ant colonies keep different fungi • Fungus is vertically transmitted • i.e. the fungal cultivar is passed down through the generations of ant colonies |
| Leafcutter ant-fungus mutualism | • This creates an opportunity for parasites: Escovopsis mould A) is a healthy attine garden B) attine garden attacked by Escovopsis |
| So how to control the mould parasite? | • Ants host bacteria that produce antibiotics and protect the ant and the fungus |
| Co-evolution of Pseudonocardia and Escovopsis - explanation? | • Pseudonocardia (bacteria): constantly evolving more effective compounds to kill Escovopsis • Escovopsis (mould): constantly evolving resistance to antibiotics |
| Competing symbiosis models:1) Vertical transmission | One coevolved species: Pseudonocardia evolving in arms-race (Red Queen) fashion against Escovopsis |
| 2) Horizontal transmission | • Ant “recruits” many useful species of bacteria from the soil • No need for an arms race, but how does the ant selectively recruit useful bacteria, since most bacteria don’t make antibiotics? |
| Testing vertical transmission | • Phylogenetics • If specific Pseudonocardia species are passed down from colony to colony, we would expect that Pseudonocardia will speciate when their leafcutter ant hosts speciate. • The phylogenies should match, showing co-speciation |
| Conclusion | Cafaro et al. concluded that some Pseudonocardia species have been recruited from the soil and passed down the generations and co-diversified and coevolved with the attine ants |
| Conclusion | Vertical transmission is a viable explanation for Pseudonocardia, but probably not the only explanation |
| Conclusion | Worsley et al. show that vertical transmission model and the horizontal transmission model can work together to produce a microbiome of antibiotic-producing bacteria, which solves the problem of maintaining effective antibiotics against Escovopsis |
Created by:
reub8n
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