Some Butterflies Have Smaller Wings, Less Color Because They Didn't Eat Enough As Caterpillars
Next time you see a less-than-colorful monarch butterfly, it is quite likely that it may have starved as a caterpillar. This, according to Haley Johnson and colleagues from University of Jamestown, who conducted experiments on the monarch butterfly and found that deprivation of food, may impact wing size and coloration, both of which are indicators of migratory success. Their research was published in the open access journal PLOS ONE on Wednesday, according to a press release.
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The monarch butterfly, probably the most famous of all American butterflies is known by its large wing size and characteristic orange and black pattern. The monarch migrates hundreds to thousands of miles during late summers or autumn to escape the harsh winter. In the United States, the monarch migrates southward to Mexico and coastal California. During spring it returns northward.
For an insect, travelling such long distances is quite a feat. And to accomplish this, the monarch requires a lot of energy, which it derives from food during early stages of its growth cycle. Ample nourishment during the caterpillar or larvae stage ensures that the adult butterfly develops proper morphology like bright coloration and appropriate wing shape and size so that it can complete its journey successfully.
The scientists came to this conclusion when they deprived late-stage larvae of milkweed, its only source of food in the wild. There were three test groups of larvae; one group had no food restriction. The second group had a 24-hour food restriction, categorized as low-stress group, and the third group had a 48-hour restriction categorized as high-stress group.
After metamorphosis, scientists imaged and analyzed the forewing length, width, and surface area, as well as the brightness of the orange wing pigment and the intensity of black pigment.
Although the effect of food deprivation was not immediately apparent on wing color and shape, the wing size was definitely altered. The researchers found that a 48-hour larval food restriction may have caused a small but clear reduction in the adult wing size, by approximately 2 percent.
So, they concluded that when larvae had limited access to milkweed, adult butterflies grew stunted wings which could ultimately result in lower success during migration. The authors also found that the quality of wing pigmentation in monarch butterflies was partly influenced by larval food supply, although the effects were unclear and require further study. Similarly, the effect on wing shape was also not easily-interpretable.
This study will have huge implications for monarch butterfly conservation efforts. Migration is a key stage in the life cycle and hence survival of a monarch. And destruction of milkweed in the larval habitat can greatly affect their populations.
Andy Davis, a member of the team, added, "There is increasing scientific and public concern over the loss of milkweeds throughout the range of monarchs in North America. Our study provides some answers to what can happen when monarch caterpillars run low on food"
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