Monarchs are shifting their migration patterns to live year-round in locations where the plants they need are always available to them, according to research from the Center for Population Biology at UC Davis. Now new investigations show that the non-migrating populations that live in the Caribbean, Central and South America, and on islands in the Pacific and Atlantic oceans actually have smaller wingspans.
The most recent is led by UC Davis graduate student, Micah Freedman, who conducted a thorough analysis of museum collections of different monarch populations. Freedman determined that while monarchs that forged the ways for new, non-migrating populations the large wings typical of the butterfly species. But over time, shows Freedman, the wings of these non-migrating populations got smaller.
Freedman’s work, which was published recently in Proceedings of the National Academy of Sciences, explains that migration naturally selects for the characteristic of longer, larger forewings; meanwhile those individuals that do not migrate do not require this characteristic, resulting in smaller wings.
Yet to test this theory, Freedman and other collaborators needed first to discard the hypothesis that environmental factors like weather, humidity, or available food sources weren’t what was influencing monarch wing size.
To do so, Freedman raised Monarch butterflies from non-migrating populations in Hawaii, Guam, Australia and Puerto Rico outside in California with native migrating Monarchs. Freedman showed that the non-migrating butterflies in fact did retain their smaller wings, meaning that the effect is due to genetics and not the environment.
"Our findings provide a compelling example of how migration-associated traits may be favored during the early stages of range expansion, and also the rate of reductions in those same traits upon loss of migration," the authors wrote.