Dipterans (two-winged insects) are thought to have evolved from a four-winged ancestor that had wings on both T2 and T3 thoracic segments, as in extant butterflies and dragonflies. Describe an evolutionary scenario for the evolution of dipterans from four-winged ancestors. What types of mutations could lead to a butterfly developing with only two wings?

Question

Accepted Answer

Hi, everyone. Let's look at our next question. Dip, terrans are believed to have evolved from four winged predecessors by what mechanism? Choice? A speciation? B genetic drift, C dual function shift or D mutation. But when we look at our four answers, there are all ways in which species evolve and become different from each other. But in this case, we're asked for a specific mechanism by which dipteran which are not this year, they're flies with two wings. So where you transition from a species with four wings to two wings. So we're looking for a more specific term than our terms of choice. A speciation, just two different groups diverging from each other enough that they can no longer interbreed or D mutation, any change to the DNA. So, speciation and mutation are just far too broad to fall under the category of a mechanism by which something evolved. When we look at choice B genetic drift, genetic drift refers to a change in genotype frequency in a small population due to random chance. So you have a small isolated population where some genotypes are lost just randomly. Um but that's not the case with flies. We're talking about lots and lots of animals, not a small isolated population. So genetic drift, choice B is not the correct answer. So we've eliminated our incorrect answers. We're down to choice C dual function shift. And that is the correct description of the mechanism by which you ended up with two winged flies from four winged ancestors. Because dual function shift refers to the modification of a preexisting structure to serve a new function. So in this case, the second set of wings in the four winged ancestors evolving to become what are called the hal tiers or halteres in flies, which are these sort of little tiny residual wings. I guess that work as sort of gyroscopic sensors allowing the flies to keep their balance in flight. So you had a preexisting structure. The second set of wings modified to serve this new function of balance while flying. So that is the correct description of a mechanism by which flies evolve from forming predecessors. So choice C dual function shift is our correct answer. See you in the next video.

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Key Concepts

Evolutionary Modification of Thoracic Segments

Homeotic (Hox) Gene Mutations

Genetic and Developmental Mechanisms of Wing Formation