The snake Dasypeltris atra feeds on bird eggs by engulfing an egg in its mouth a

Question

The snake Dasypeltris atra feeds on bird eggs by engulfing an egg in its mouth and crushing it in its throat. In one area, the usual small birds were replaced by aggressive starlings. Starlings lay larger eggs that are difficult for most D. atra to swallow. Before the starlings took over, the mean gape size in 73 snakes was 31 mm, and in 33 snakes that survived after starlings arrived it was 35 mm. It offspring of the surviving snakes had gapes that were on average 6% larger than the population before the starlings, what was the narrow-sense heritability of gape size? Show the formula and all calculations.

Explanation / Answer

Narrow sense heritability, h2 is defined as the ratio of response to selection(R) to the selection differential(S).

i.e h2= R/S

where R= (mean value of the offspring of the selected individuals) - ( mean value of the selected individuals )

S=(Mean value after selection) - (mean value before selection)

here the selected indiviuals means those individuals survived after selection.

In this case, selection process is the replacement of small birds by aggressive starlings.

1. Since it is given that the offsprings had a mean gape size which is 6% larger than the population before selection,

Mean gape size of the offsprings of the selected snakes= 31+ 6% of 31 = 31+[(6/100)*31] = 31+1.86 = 32.86

Mean gape size of snakes after selection= 35

So, R= 32.86 - 35 = -2.14

Mean gape size of snakes before selection= 31

Therefore, S= 31- 35 = -4

h2= -2.14/ -4 = 0.535

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