Migration distance as a selective episode for wing morphology in a migratory insect

Abstract

BackgroundSelective pressures that occur during long-distance migration can influence morphological traits across a range of taxa. In flying insects, selection should favour individuals that have wing morphologies that increase energy efficiency and survival. In monarch butterflies, differences in wing morphology between migratory and resident populations suggest that migratory populations have undergone selection for larger (as measured by length and area) and more elongated (as measured by roundness and aspect ratio) forewings. However, selection on wing morphology may also occur within migratory populations, particularly if individuals or populations consistently migrate different distances.ResultsUsing 613 monarch butterflies that were collected on the Mexican wintering grounds between 1976 – 2014, we tested whether monarch wing traits were associated with migratory distance from their natal areas in eastern North America (migration range: 774–4430 km), as inferred by stable-hydrogen (δ 2H) and -carbon (δ 13C) isotopic measurements. Monarchs that migrated farther distances to reach their overwintering sites tended to have longer and larger wings, suggesting positive selective pressure during migration on wing length and area. There was no relationship between migration distances and either roundness or aspect ratio.ConclusionsOur results provide correlative evidence that the migratory period may act as a selective episode on monarch butterfly wing morphology, although selection during other portions of the annual cycle, as well as extensive mixing of individuals from various natal locations on the breeding grounds, likely counteracts directional selection of migration on morphology.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-017-0098-9) contains supplementary material, which is available to authorized users.

Phytochemical changes in milkweed induced by elevated CO2 alter wing morphology but not toxin sequestration in monarch butterflies

“…Therefore, our data substantiate previous studies demonstrating strong selection for larger wings imposed by migration distance within this population (Altizer & Davis, ; Li et al, ). Forewing size is likely more important to migration success than wing shape because it is conserved among all our treatments and is selected for in the migratory populations of monarchs (Altizer & Davis, ; Flockhart et al, ; Li et al, ). However, aerodynamic theory suggests that wing shape can be important for manoeuvrability and energy conservation (Pennycuick, ).…”

“…In addition to sequestration, the seasonal migration of monarchs may also reduce mortality imposed by natural enemies. In eastern North America, monarchs migrate up to 4,500 km from their summer breeding grounds to overwintering sites in Mexico every fall (Urquhart & Urquhart 1978;Brower & Malcolm, 1991;Flockhart et al, 2017). For many flying animals, foraging, escape and migration are strongly influenced by wing size, shape and wing loading, the ratio between body mass and wing area (Berwaerts, Van Dyck, & Aerts, 2002;Dudley, 2002).…”

Patterns of parasitism in monarch butterflies during the breeding season in eastern North America

“…(), the model calculated a probability of natal origin to each pixel (resolution: 0.1667°) in our study area based on the correspondence between δ 2 H and δ 13 C values in wing tissue to the isoscape‐predicted values of monarch δ 2 H and δ 13 C wing tissue of each geographically indexed cell in the landscape from Flockhart et al . (). Details of probabilistic assignment of natal origin follow those presented in Wunder () and Flockhart et al .…”

“…Details of probabilistic assignment of natal origin follow those presented in Wunder () and Flockhart et al . ().…”

“…We used multivariate normal distribution assignment models to calculate the probability of natal origin to each pixel in a continuous landscape that spanned the monarch breeding distribution (Royle & Rubenstein, 2004;Miller et al, 2011). For each butterfly in Flockhart et al (2013), the model calculated a probability of natal origin to each pixel (resolution: 0.1667 ∘ ) in our study area based on the correspondence between 2 H and 13 C values in wing tissue to the isoscape-predicted values of monarch 2 H and 13 C wing tissue of each geographically indexed cell in the landscape from Flockhart et al (2017b). Details of probabilistic assignment of natal origin follow those presented in Wunder (2010) and Flockhart et al (2017b).…”