In 1983 a population of dark-eyed junco birds became established on the campus o
ID: 18317 • Letter: I
Question
In 1983 a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco’s normal habitat in the mixed-coniferous temperate forests in the mountains.Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males, and display it less often.
Based on the information given above, which of the following types of selection was most likely initially involved in the evolution of white outer tail feathers in juncos?
1. directional selection
2. stabilizing selection
3. disruptive selection
4. sexual selection
5. None of the above
Explanation / Answer
dear answer is : 4
Colonization of novel environments creates new selection pressures. Sexually selected traits are affected by the physical and social environment and should be especially susceptible to change, but this has rarely been studied. In southern California, dark-eyed juncos, (Junco hyemalis) naturally breed in mixed-coniferous temperate forests, typically from 1500 m to 3000 m in elevation. In the early 1980s, a small population became established in a coastal habitat, the University of California, San Diego campus, which has a mild, Mediterranean climate. I show that a sexually and socially selected signaling trait–the amount of white in the tail–has declined by approximately 22% as compared to mountain juncos. I address three main factors that could explain the difference between mountain and coastal juncos: phenotypic plasticity, genetic drift, and selection.
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