| Abstrakt: |
Monarch butterflies (Danaus plexippus) are well studied for their annual long‐distance migration from as far north as Canada to their overwintering grounds in Central Mexico. At the end of the cold season, monarchs start to repopulate North America through short‐distance migration over the course of multiple generations. Interestingly, some populations in various tropical and subtropical islands do not migrate and exhibit heritable differences in wing shape and size, most likely an adaptation to island life. Less is known about forewing differences between long‐ and short‐distance migrants in relation to island populations. Given their different migratory behaviors, we hypothesized that these differences would be reflected in wing morphology. To test this, we analyzed forewing shape and size of three different groups: nonmigratory, lesser migratory (migrate short‐distances), and migratory (migrate long‐distances) individuals. Significant differences in shape appear in all groups using geometric morphometrics. As variation found between migratory and lesser migrants has been shown to be caused by phenotypic plasticity, and lesser migrants develop intermediate forewing shapes between migratory and nonmigratory individuals, we suggest that genetic assimilation might be an important mechanism to explain the heritable variation found between migratory and nonmigratory populations. Additionally, our research confirms previous studies which show that forewing size is significantly smaller in nonmigratory populations when compared to both migratory phenotypes. Finally, we found sexual dimorphism in forewing shape in all three groups, but for size in nonmigratory populations only. This might have been caused by reduced constraints on forewing size in nonmigratory populations. Research Highlights: Monarch butterflies (Danaus plexippus) are well known for their annual long‐distance migration from as far north as Canada to their overwintering grounds in Central Mexico, followed by a multigenerational return at the end of the cold season. However, some tropical populations do not migrate and exhibit heritable differences in wing shape and size, most likely an adaptation to island life. Less is known about forewing differences between individuals which travel to the south (long distance) when compared with individuals which migrate north through several generations (short distance). We compared forewing shape between all three groups (long‐distance, short‐distance, and nonmigratory) and found differences between all groups measured, with short‐distance individuals being intermediate. As long‐ and short‐distance migratory monarch phenotypes have been shown to be caused by changes in the composition of their food source as a caterpillar, we suggest that genetic accommodation might be an important mechanism to explain the heritable variation found between migratory and nonmigratory populations. [ABSTRACT FROM AUTHOR] |
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