Question

2. Morran et al. 2011 tested the Red Queen Hypothesis with an experiment on populations of the roundworm Caenorhabditis elegans. Populations of C. elegans include both males and "hermaphrodites" (individuals capable of producing both male and female gametes). Hermaphrodites can reproduce alone (termed selfing i.e., asexual reproduction) or mate with males (termed outcrossing i.e., sexual reproduction). The rate of outcrossing in a population can be used as an index of how much selection is favoring sexual reproduction (outcrossing) over asexual reproduction (selfing). : To test the Red Queen Hypothesis, researchers placed 5 replicate lab populations of C. elesans in each of the following treatments: - • "Control": no exposure to the infectious bacterium Serratia marcescens • "Evolution": periodic exposure to S. marcescens from a frozen (non-evolving) source population. 3 "Coevolution": periodic exposure to s. marcescens from a population allowed to evolve to become more infectious.. The researchers allowed all 15 populations C. elegans to evolve for 30 generations in each treatment. They monitored what percentage of the population was composed of males as a way to measure how often sexual reproduction (outcrossing) was occurring. The results of the experiment are presented in the graph below: 3

Answer 1

a. Results of all three treatments

Control: Here the populations of Caenorhabditis elegans have no exposure to the infectious bacterium Serratia marcescens. The percentage of males evolved in further generations did not show much variance. That means selection favoring sexual reproduction which will help the organism to adopt did not progress much as there was no negative consequence environmentally.

Evolution : In the second set of population, when C. elegans were periodically exposed to non-evolving strains of S.marcescens , we could see there are various spikes and dips in the graph. That means their periodic exposure did have an impact on the outcrossing rate. That explains when the environment is adverse, there could be occasional favoring of sexual reproduction(outcrossing), however there was a dip by the 30th generation, because of the fact that strains of the bacterium are less virulent and C.elegans already evolved to resist the same.

Coevolution : Here C.elegans was exposed to the strain of S.marcescens that evolved to be more toxic and infectious. The graph clearly indicates an overall increase in the outcrossing rate, which favors sexual reproduction, allowing the worms to evolve to the adverse environment.

b. Red Queen Hypothesis mentions that organisms must constantly evolve, adapt and proliferate in order to survive in adverse environments when they are with constantly evolving organisms in an environment that changes constantly. In the experiment, when the worm was kept with the bacterium that was most virulent and evolving we could see the maximum rate of outcrossing which helps the worms to reproduce sexually and hence taking the advantage of co-evolution of sexual reproduction to evolve in the harsh environment. Hence it absolutely supports Red Queen Hypothesis.

c. The evolution treatment shows that the ability of an organism to evolve is directly proportional to the adverse conditions in the environment. It is important to test RQH as it helps to study predator-prey relationships as predators and preys have to constantly evolve to avoid extinction. It can be applied to aquaculture and farming where the host can escape parasites by adopting.