Question

Assuming that mutant mosquitoes were rare prior to the introduction of DDT, sequence the events that may have initially caused mosquito populations to develop resistance to DDT.

1) DDT was sprayed on surfaces regularly contacted by mosquitoes.
2) Mosquito populations became highly resistant to DDT.
3) Scientists believe that DDT resistance first evolved with a mutation in genes coding for sodium ion channels in mosquito neurons.
4) Mutant mosquitoes were rare prior to the introduction of DDT.

Answer 1

Mosquito populations initially developed resistance to DDT through a combination of factors. Mutations caused the allele for DDT resistance to appear, and the wide use of DDT favored fruit flies with DDT resistance, making them more evolutionarily fit. Additionally, female mosquitoes chose to mate with male mosquitoes that had the allele, increasing the frequency of DDT resistance in offspring.

Step-by-step explanation:

1. The wide use of DDT meant that fruit flies with DDT resistance were more evolutionarily fit than their counterparts without DDT resistance.
2. Mutations from the application of DDT caused the allele conferring DDT resistance to appear in the population.
3. Female mosquitoes chose to mate with male mosquitoes that had the allele conferring DDT resistance because it would make their offspring more fit.

The development of DDT resistance in mosquito populations began with a genetic mutation that provided resistance to the pesticide. This resistance became an evolutionary advantage as DDT was widely used, allowing resistant mosquitoes to survive and reproduce more effectively than non-resistant ones, thereby spreading the resistance allele throughout the population.

The sequence of events leading to mosquito populations developing resistance to DDT starts with a random mutation. Mutations may have initially caused the resistance to DDT, as suggested by scientists, due to a change in the genes coding for sodium ion channels in mosquito neurons. This genetic alteration occurs prior to the widespread use of DDT. When DDT was sprayed regularly to control mosquito populations, it was effective because of its persistence and resistance to environmental breakdown.

Unfortunately, this also meant that mosquitoes with the resistance allele had a survival advantage. Since DDT killed off a large proportion of mosquitoes without resistance, the ones with the allele were more likely to survive and reproduce. This resulted in the allele for DDT resistance becoming more common in the population. Subsequent generations saw an increase in DDT-resistant mosquitoes, making the chemical less effective over time and leading to a high level of resistance in populations.

Female mosquitoes are more likely to choose mates that possess this resistance allele, as it increases the fitness of their offspring in an environment where DDT is present. The result is a rapid spread of resistance through the mosquito population. This is an example of microevolution, where the genetic composition of the population changes in response to an environmental pressure—in this case, the application of DDT. This resistance development was also observed in other insect species, similar to the reports of houseflies in Sweden in 1946.

In conclusion, a combination of genetic mutation, selective survival due to pesticide application, and reproductive choices led to the widespread development of DDT resistance among various insect populations.