Clines in body size have been observed in many species, such as the latitudinal

Question

Clines in body size have been observed in many species, such as the latitudinal cline in moose.

Does a cline in body size necessarily result
from variation in allele frequencies at loci that
affect body size? Why or why not?

How might you determine whether a cline
in body size was caused by clines in allele
frequencies?

Say there is strong evidence that a latitudinal
cline in body size in a squirrel is caused by
variation in allele frequencies. Do you think
that data showing how rapidly the average
body size changes with latitude could by
themselves be used to determine how selection varies in space? Why or why not?

Explanation / Answer

Note that clines occur because of environmental heterogeneity. The change in environment can further cause change in allele for body size of moose. But it is not necessary that variation of the allele frequency at a particular locus is responsible for the cline change; simply the environmental factor can also cause the change.

If you want to determine clines for body size, then sequencing of alleles can be done. This will tell you whether the allele frequencies were responsible for body size change or not.

No, the data that shows that average body size varies (in squirrels) with variation in allele frequencies is not a complete indicator of selection in space.

Selection in space is dependent on natural selection, genetic drift, and migration also. Only cline difference/allele frequency difference is not responsible for selection of a particular group of organisms in space.

But you can say that natural selection, genetic drift and migration is monitored by certain geographical gradations, and these gradations are called as clines. So, partly your statement "the average body size changes with latitude could by themselves be used to determine how selection varies in space" is correct also.

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