PARENT SESSION
Poster Session # 21: Biogeography, Biodiversity, Populations, and Genetics.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Geographic variation among monarch butterfly populations: Migratory behavior and the evolution of wing morphology.

Davis, Andrew^*,1, Altizer, Sonia¹, Vitone, Nicholas¹, ¹ Dept. of Environmental Studies, Atlanta, GA, USA

ABSTRACT- Native and introduced monarchs populate islands and continents worldwide, including North and South America to Hawaii, Australia, and New Zealand. In parts of North America and Australia, monarchs undergo an annual migration (traveling up to 2000 km to overwintering sites), whereas monarchs in resident populations breed continuously and do not migrate. For decades, scientists have assumed that monarchs from these different regions were genetically distinct, yet almost no empirical studies have addressed this issue directly. We examined geographic variation in wing morphology among monarch butterfly populations in 2 migratory and 2 non-migratory populations in N. America. We used both wild-caught monarchs and captive-reared progeny from eastern N. America (migratory), western N. America (migratory), southern Florida (resident), and Hawaii (resident). We scanned the forewings of monarchs from each of these populations and quantified size, color and shape characteristics using image analysis software. Based on comparisons of migratory and non-migratory bird species, we predicted that monarchs from migratory populations will have more sharply angled and more pointed forewings, while non-migratory populations would have more rounded wings. Consistent with our predictions, monarchs from resident populations had shorter forewings (and smaller wing areas) than monarchs from migratory populations. We further detected significant population-level differences in wing shape, with the highly migratory eastern monarchs having the most angular and pointed wing design, similar to that found in migratory bird species. Finally, we found that monarchs from both resident populations had significantly darker forewings than monarchs from migratory populations. Comparison of wild and captive-reared butterflies indicates that these differences are not solely environmentally driven and are heritable between generations. This study increases our understanding of the genetic basis of population divergence among insect populations separated by geographic barriers or migratory divides.

Key words: migration, evolution, monarchs, wing morphology