Key Area 2
(c) Co-evolution
In this section, we will learn about how the evolution of one species can exert selection pressures on another species, resulting in co-evolution.
Institute of Evolutionary Biology, University of Edinburgh
The Institute of Evolutionary Biology at the University of Edinburgh studies evolution "in the broadest sense possible". This includes research into viral and bacterial evolution, exploring methods of phylogenetic analysis (as discussed in Key Area 1) and host-parasite co-evolution. The research carried out relies on experts from a broad spectrum of disciplines including maths, physics, engineering, computer sciences, informatics, chemistry, biology and medicine. Today's cutting edge Science is truly inter-disciplinary. The best results are always achieved in collaboration with others.
Co-evolution is the process by which 2 or more species evolve in response to selection pressures imposed by each other. A change in the traits of one species acts as a selection pressure on the other species.
Co-evolution often results in symbiosis - co-evolved intimate relationships between members of 2 different species. There are three types of symbiotic relationships.
Mutualism
Both organisms in the interaction are interdependent on each other for resources or other services. As both organisms gain from the relationship, the interaction is (+/+).
The relationship between the sea anemone and clownfish is an example of mutualistic symbiosis. The clownfish is protected by the stinging tentacles of the anemone, and keeps zebrafish away, forming a mutualistic relationship.
Commensalism
Only one of the organisms benefit from the interaction (+/0).
An example is the relationship between pilot fish (Naucrates ductor) and a whitetip shark (Carcharhinus longimanus). The pilot fish swim alongside the shark for protection, without causing harm or benefit to the shark itself.
Parasitism
The parasite benefits in terms of energy or nutrients and the host is harmed as the result of the loss of these resources (+/-).
A crustacean called the tongue-eating louse targets fish, such sand steenbras (see image). It attaches itself to the base of the fish tongue until the tongue detaches due to blood loss. The louse then fastens itself to the tongue stub, functioning as the fish’s tongue from that point on.
Task 19
"I can't believe those sharks can be bothered with those wee fish hanging on the whole time. How is that a +/0 relationship?! It'd do my heid in if they wouldne leave me alone all day and night. Definitely be negative for me if I was the shark", Big Davie complained about the example posed for Commensalism.
Dr McRobbie went on to explain that the shark suffered no loss of resources, to which Big Davie complained that she had not factored in the shark's mental wellbeing. "Well, then Mr MacKay, perhaps you could come up with a more acceptable example in this next task".
He'd talked himself into another bloomin' task - he really didn't know how he did it so often!
"Right everyone, in box 19, describe one example of each symbiotic relationship we have explored - be very clear on why each has been assigned (+/+), (+/0) or (+/-)!
Suggested answers are here.
Co-evolution is frequently seen in pairs of species that have symbiotic interactions. This includes herbivores and plants; pollinators and plants; predators and prey; parasites and hosts. More details are given below.
Herbivores & plants
In the example above, old world swallowtail caterpillar feeds on the rue plant. The plant produces toxic oils to deter insects; the caterpillar has evolved tolerance to these oils to enable it to continue feeding.
Pollinators & plants
Symbiosis between plants and pollinators is an example of mutualism. Darwin's moth, shown above, has co-evolved with a particular orchid to ensure the moth receives nutritious nectar and then spreads pollen so both can reproduce.
Predators & prey
Predator-prey relationships are those involving predation, in which a predator eats its prey. Successful predators may have evolved adaptations, e.g. claws, teeth, fangs and poison. Prey species also evolved adaptations, including camouflage and speed to help them escape.
Parasites & hosts
Parasitism involves a relationship where a parasite lives on a host, gaining resources and a habitat. An example is the co-evolution between the parasite that causes malaria, the mosquito that acts as a vector for the parasite and humans, which are the host.
Fossil evidence suggests that the parasite responsible for causing malaria started to spread extensively approximately 100,000 years ago. This timeline aligns well with the first major migrations of humans.
DNA sequence analysis suggests that both the parasite and the mosquitoes have evolved rapidly, providing strong evidence for the co-evolution of each organism resulting from selection pressures placed on each by the other.
Another side of this rapid co-evolution is that human endeavours towards drug development against malaria can be thwarted. The parasites evolve resistance and malaria continues to pose grave threats globally - this is highlighted in the animation (left; white button).
Task 20
Conduct your own research into co-evolved pairs of species that have not been mentioned above. Your response must include:
a co-evolved herbivore and plant relationship
a co-evolved pollinator and plant relationship
a co-evolved predator and prey relationship
a co-evolved parasite and host relationship
Suggested answers are here.
Use the Padlet below to share some of your cool examples of co-evolution.
The Red Queen Hypothesis
The Red Queen hypothesis states that, in a co-evolutionary relationship, change in the traits of one species can act as a selection pressure on the other species.
This means that species in these relationships must adapt to avoid extinction.
The hypothesis states that both organisms must “keep running in order to stay still”.
In Alice in Wonderland, the Queen says to Alice that she can keep running but she will stay in the same place.
Dog Lover? If so, here is a fantastically interesting account of the domestication of dogs with some scientists suggesting they co-evolved with humans. Veterinarian Karen Becker explains their journey.
Task 21
Complete the questions in the slides below. The answers to these questions are in the final slides.
Now go to SCHOLAR to:
2.3 - Co-evolution
2.4 - Learning points
2.5 - End of topic test
Time to create your own content for our online class blog and become a published author! Write a piece that showcases your learning of Key Area 2 on Evolution.
Your teacher might now issue you with Learner Check 14 to check your learning of Topic 2, Key Area 2.
You have now completed Topic 2, Key Area 2. Fantastic work! You have earned from chill-out time, similar to these otters.
But, you are now ready to move onto Key Area 3, all about Variation and Sexual Reproduction!
