Female
Drosophila pseudoobscura are
polyandrous, meaning they mate with more than one male. By mating with multiple males, polyandrous females have more genetically diverse offspring.
Fitness benefits Prevention of extinction In the
D. pseudoobscura population, some males have a harmful chromosome called sex ratio (SR), where an inactive Y-chromosome is transmitted. If an SR male mates with a female, the female will produce only daughters. Monandry allows the spread of SR and increases the extinction risk in species having SR genes because the SR driver can spread quickly, enriching populations for females. Polyandry decreases the SR gene frequency because the non-SR male sperm outcompete the SR male sperm. Therefore, polyandry results in a decreased risk of extinction in the population.
Increased net offspring survival Monandrous female
D. pseudoobscura do not obtain sufficient sperm or a plenty of suitable sperm for the fertilization. Even though monandrous female experiencing multiple copulations can produce more eggs than polyandrous female experiencing multiple
copulations, monandrous females produce less offspring that survive into adulthood than polyandrous females do.
Evolutionary consequences Polyandry, in general, may have a few fitness consequences. Densely populated areas may have lower rates of polyandry due to environmental restraints such as geographic location and limited resources. This can greatly limit the survival and reproduction of offspring. Therefore, in population dense areas, polyandrous behavior may actually be a fitness consequence since the environment significantly controls the number of offspring that survive. As a result, attractive individuals are more likely to reproduce more often. However, since these individuals do not always contain adaptive genes, multiple mating events do not always result in the propagation of adaptive genes. == Pheromones ==