Mimamsa 2025
There are known to exist two populations of grasshoppers(A and B, both isolated from each other) on a faraway island. These grasshoppers are known to only breed once in their lifetime. Genetic analysis reveals a heritable trait in all grasshoppers of population B, that makes individuals mate exclusively with their full siblings, whereas grasshoppers of population A only mate with non-siblings. This trait is not present in any individual of population A, and doesn't (directly or indirectly) cause detrimental effects in B grasshoppers.
Assumptions:
Males can mate with multiple females during a single breeding season, but females can mate only once.
a. Assuming the populations have existed for a very long amount of time in stable environments, predict the sex ratio (males and females) in populations A and B. Assume the populations to be stable (i.e., neither increasing nor decreasing after a very long time).
Assume males and females to have the same survival rates, i.e., equal percentages of males and females survive to the reproductive phase.
b. How will your answer to (a) change if the percentage of males and females reaching the breeding season is different? Give a proper explanation for your answer.
c. Aditya introduces 5000 female and 1000 male grasshoppers from both populations into two isolated habitats, where a habitat comprises only individuals from the same population. The populations are then observed for multiple generations. Plot the variation in sex ratio for both habitats over time. Assume the initial B population contains many sets of siblings.
d. A subpopulation of 1000 individuals (having a sex ratio equal to the stable ratio calculated in part (a)) from population B is isolated. It is observed that for some reason, approximately half of the population has lost the sibling-mating trait and now mates only with non-siblings. Predict the change in sex ratio, and trait frequency (number of individuals who mate strictly with siblings / total population size) over a period of time. Assume that there exist sets of siblings in the subpopulation that have not lost the trait.
Assume populations A and B are identical in every aspect except mating behaviour, as outlined above.