Which of the following is not an example of a prezygotic barrier to reproduction between two potentially separate species?
a. a race of flies raised on apple and a race of flies raised on hawthorn emerge in different seasons in response to the timing of fruit ripening.
b. eggs of chickens cannot be fertilized by the sperm of ducks.
c. the specialist pollinating wasps of fig species a are unable to access the flowers of fig species b, and vice versa
d. two closely-related species of anopheles mosquito can mate but cannot produce fertile progeny because they have different chromosome structures.
e. the courtship “waving signal” of male fiddler crabs is unique to each species so that females only respond to the mating display of males of their own species.

D

Explanation:

Prezygotic barriers prevent gametes from two potentially different species from fusing and forming a hybrid. The types of prezygotic barriers are ecological (differences in habitat), temporal (reproduction occurs at different times), mechanical (copulation is prevented due to differences in sexual organs or other anatomical differences), behavioral (mating behavior differs) and gametic (gametes are incompatible or are not attracted to each other).

In this question, A is an example of a temporal prezygotic barrier because the flies emerge at different times thus reproduction times between these two races of flies are not in sync.

B is an example of a gametic prezygotic barrier because the eggs of chickens are incompatible to the sperm of ducks.

C is an example of a mechanical prezygotic barrier because the wasps have specialized anatomical differences that prevent them from accessing the flowers of other species of wasps to mate.

E is an example of a behavioral prezygotic barrier because females of the fiddler crabs are only attracted to their own species courtship "waving signal"

D is not an example of a prezygotic barrier because the two species of mosquitoes can mate and do produce progeny, however there is a postzygotic barrier as the progeny are not fertile. This is an example of hybrid sterility.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation: