Chapter 17, Problem 1NS.1QC

Summary Introduction

To determine:

How microevolutionary changes in BMP4 and $CaM$ genes lead to speciation in finches.

Introduction:

BMP4 (bone morphogenetic protein 4) is a gene that is responsible for the beak depth in the finches. On the other hand, $CaM$ is a gene called calmodulin that determines the length of the beaks in finches. These genes’ activity is not limited to finches only.

Explanation of Solution

Speciation happens when macroevolution happens. Macroevolution is the culmination of many small microevolutions. The causal forces behind these are selection, mutation, migration and more. The following example can illustrate how microevolutionary changes in BMP4 and $CaM$ genes lead to speciation in finches:

The environment of a finch population has large seeds. The finches have long and shallow beaks to feed on these. Due to dry climate, large seeds decline and small seeds increase. To consume these, the beaks must be short and deep.

Thus, the expression of BMP4 increases to deepen the beak and activity of $CaM$ reduces to shorten the beak. If the dry climate extents to a longer period, the gene expression modifies permanently as mentioned to produce a species of finches that have short and deep beaks to feed on small seeds. Even when the conditions turn back to normal and large seeds are available again, they will still feed on small seeds. Thus a new population has originated (speciation) via macroevolution by the accumulation small evolutionary changes in the BMP4 and $CaM$ genes over time.

Conclusion

When microevolutionary changes accumulate over time, it pulls two populations so far apart that they form new species (macroevolution).