Explain the following: Lamarck\'s lizards live on the beaches of Eberhart Island

Question

Explain the following:

Lamarck's lizards live on the beaches of Eberhart Island, where there are black, grey, and white rocks. The lizards come in three colors; black (Genotype BB), grey (Bb), and white (bb). The allele frequencies are 0.5 and 0.5. While the population is preyed upon by Darwin's Hawks, predation is random. The population is in Hardy Weinberg equilibrium.

A number of the lizards are brought to Sullivan island, which also has Darwin's hawks, but only black and white rocks. The number of lizards was large enough and the genotype frequencies the same, so Genetic Drift, including the Founder Effect, did not occur.

a) What sort of selection would act on the lizards living on Sullivan Island?

b)What behavioral adaptation might be favorable for the lizards on Sullivan Island but selectively neutral for those on Eberhart (hint: Think about the other H-W assumptions)? Why would this be favorable?

c) What may happen to the lizards on Sullivan, compared to those on Eberhart?

Explanation / Answer

Scenario:
Eberhart island - Black, grey and white rocks present. Black (BB), Grey (Bb) and White (bb) lizards.
Sullivan island - Black (BB), Grey (Bb) and White (bb) lizards. But only black and white rocks.

a) On Sullivan island the grey lizards will get selectively preyed upon. This is because white lizards have white stones and black lizards have black stones available for camouflage and hiding from the predator but gey lizard doesn't have this advantage (which it had on Eberhart island). Predatory pressure will act more on the grey lizard and their number will start to decrease.

b) The most important assumption of H-W assumption is that the mating is random. On Eberhart island the mating is random and it is selectively neutral because the predation is also random (no color specific advantage). But in the case of Sullivan island it is not so.
Hence, Sullivan lizards would behaviorally adapt such that black (BB) mates with black (BB), white (bb) mates with white (bb) and grey (Bb) mates withe grey (Bb). This behavioral adaptation will be favorable for the lizards because this will produce maximum amount of Black or White lizards and go on reducing the number of grey lizards (which have lesser selective advantage) every generation.
(BB x BB gives all black (BB) progeny, bb x bb gives all white (bb) progeny, Bb x Bb gives 25% black (BB), 25% white (bb) and 50% grey (Bb) progeny)

Thus we can see that a phenomenon called inbreeding is happening and it will go on reducing the heterozygous genotype (Bb).

c) As established in part b of the answer, Eberhart still has random mating but the Sullivan lizards have sought to inbreeding. Therefore, the Eberhart lizards will remain in H-W equilibrium.
On Sullivan island, predatory pressure along with the result of inbreeding will reduce the grey (Bb) population to zero. The behavioral adaption of mating with same color might persist even after the removal of grey lizards. This might result in formation of two biologically different species after sufficient generations.

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