Question

Two subspecies of salamanders in Southeast Asia, salamander S1 and Salamander S2, are thought to have diverged genetically and morphologically through run speciation. At the souther tip of their respective native ranges, they can co-occur in secondary contact. They can mate successfully and produce viable, fertile offspring; the offspring can therefore also reproduce. However, the hybrid offspring have a coloration that is disproportionately attractive and easily detectable by predators, leading to decreased survival.

The relatively low fitness of the S1 x S2 hybrid salamander would be an example of:

a. post zygotic behavioral isolation

b. gametic incompatibility

c. mechanical isolation

d. reinforcement

e. prezygotic isolation

Assuming that mating occurs freely in secondary contact, what is the fitness of the parent salamanders S1 and S2 in the scenario?

a. low. fitness involves reproductive success and survival; if survival is low in the offspring, the parents cannot pass their genes on to future generations

b. zero.

c. high. fitness involves reproductive success and survival, the parents are reproductively successful and able to survive

d. high. fitness of the parents is not related to fitness the progeny

e. none of the above

Answer 1

Question 1 answer - d. Reinforcement.

Explanation- The low viability of hybrid in this case is due to reinforcement selection which promotes speciation and prevents gene flow between members of S1 and S2 and also tries to maintain intactness of these groups. Therefore the progeny produced by each group S1 or S2 separately are more viable and progeny produced by hybridization of S1 & S2 are are less viable. This mechanism for "reinforcing" hybridization barriers in sympatric populations is also known as the "Wallace effect", as it was first proposed by Alfred Russel Wallace at the end of the 19th century, and it has been experimentally demonstrated in both plants and animals.

Question 2 answer- d. High. Fitness of parent salamander is not related to fitness of progeny.

Explanation - As explained in previous question also that S1 and S2 are fit independently and their pure breeding of offsprings are also viable but the progeny produced by cross between S1 and S2 are less viable which is due to reinforcement selection and their low viability is not related to fitness of their parents.