Question

Which example provides evidence of migration, but NOT of gene flow? After fledging, a male toucan disperses to another forest patch on the other side of a mountain range. This high-quality male finds mates easily in this new population. All of its offspring survive to breed in the next year in the same forest patch. A bearcat eats the fruit of a strangler fig tree and defecates seeds 10 km away among a different population of strangler figs. A hiker gets mustard seeds stuck in their shoe. They travel across the country and hike a different trail unintentionally dispersing mustard seeds into the current population of mustard plants. These seeds develop into plants that then contribute to the next generation. A couple of snakes from the mainland are swept away by a storm and carried to a nearby island. On the island, these snakes breed with the same species and produce viable offspring.

Answer 1

Migration is the large scale movement of organisms from one environmental condition to another. it may be seasonal or occasional. It is done by diverse group of organisms to cope up with adverse condition of habitat (migration of Siberian Cranes), to search for a better feeding and breeding (migration of Salmon fish from sea to fresh water body for breeding). Migration is a relatively temporary movement which necessarily do not account for the change in allele frequency of existing population, which is termed as the Gene Flow. Gene flow occurs when the genetic material of one population is transferred to another population. Gene flow is the indirect measure of extent of Migration in that specific sub-population. But, every migration does not lead to gene flow.

From the above examples, those which are migration but do not contribute to gene flow are listed below:

i- A bearcat eats the fruit of a strangler fig tree and defecates seeds 10 km away among a different population of strangler figs.

Only the dispersal of seed does not account for gene flow. Genetic variability comes only if there is mating between individuals of two population.

ii- A couple of snakes from the mainland are swept away by a storm and carried to a nearby island. On the island, these snakes breed with the same species and produce viable offspring.

As breeding is occurring between the same species, no genetic variability will be seen, and so there is no evidence for gene flow.

In all other examples, migrating organisms mate with the individuals of existing population to give birth to viable progenies, introducing new sets of alleles in the population, thus contributing to gene flow.