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

AbstractThe migration of monarch butterflies (Danaus plexippus) in North America has a number of parallels with long-distance bird migration, including the fact that migratory populations of monarchs have larger and more elongated forewings than residents. These characteristics likely serve to optimize flight performance in monarchs, as they also do with birds. A question that has rarely been addressed thus far in birds or monarchs is if and how wing characteristics vary within a migration season. Individuals with superior flight performance should migrate quickly, and/or with minimal stopovers, and these individuals should be at the forefront of the migratory cohort. Conversely, individuals with poor flight performance and/or low endurance would be more likely to fall behind, and these would comprise the latest migrants. Here we examined how the wing morphology of migrating monarchs varies to determine if wing characteristics of early migrants differ from late migrants. We measured forewing area, elongation (length/width), and redness, which has been shown to predict flight endurance in monarchs. Based on a collection of 75 monarchs made one entire season (fall 2010), results showed that the earliest migrants (n = 20) in this cohort had significantly redder and more elongated forewings than the latest migrants (n = 17). There was also a non-significant tendency for early migrants to have larger forewing areas. These results suggest that the pace of migration in monarchs is at least partly dependent on the properties of their wings. Moreover, these data also raise a number of questions about the ultimate fate of monarchs that fall behind

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Population-specific patterns of toxin sequestration in monarch butterflies from around the world

10.1101/2021.10.15.464593 ◽

2021 ◽

Author(s):

Micah Freedman ◽

Sue-Ling Choquette ◽

Santiago Ramirez ◽

Sharon Strauss ◽

Mark Hunter ◽

...

Keyword(s):

Genetic Variation ◽

Species Interactions ◽

Evolutionary History ◽

Host Plants ◽

Strong Support ◽

Population Level ◽

Oceanic Island ◽

Asclepias Syriaca ◽

Monarch Butterflies ◽

Toxin Sequestration

Monarch butterflies are one of the preeminent examples of a toxin-sequestering animal, gaining protection against predators via cardenolides obtained from their milkweed host plants. Although cardenolide sequestration by monarchs has been studied in ecological, physiological, and phylogenetic contexts, relatively little research has surveyed genetic variation in the ability to sequester, nor has monarch sequestration been studied in relation to divergent host plant assemblages or variation in exposure to predation. Here, we use the monarch's recent global range expansion to test hypotheses about how cardenolide sequestration evolves over relatively contemporary time scales. First, we test for whether sympatric monarch/milkweed combinations have a sequestration advantage by rearing six geographically disparate monarch populations on six associated milkweed host species and measuring levels of sequestered cardenolides in a set of 440 adult butterflies. Second, we use monarchs from Guam - an oceanic island where birds have been functionally extirpated for approximately 40 years - to test hypotheses about how exposure to avian predation affects cardenolide sequestration. We find little overall evidence for increased sequestration on sympatric hosts. However, one monarch population (Puerto Rico) shows strong support for cross-host tradeoffs in sequestration ability, primarily driven by limited sequestration of polar cardenolides from two temperate North American milkweeds (Asclepias syriaca and A. speciosa). Monarchs from Guam show some evidence for reduced cardenolide sequestration in both a cross-island comparison of wild-caught butterflies as well as population-level comparisons of greenhouse-reared butterflies. Our results suggest that there is substantial genetic variation in sequestration ability (both within and between monarch populations) and that evolutionary history and contemporary species interactions may influence patterns of cardenolide sequestration.

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Hox dosage contributes to flight appendage morphology in Drosophila

Nature Communications ◽

10.1038/s41467-021-23293-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Rachel Paul ◽

Guillaume Giraud ◽

Katrin Domsch ◽

Marilyne Duffraisse ◽

Frédéric Marmigère ◽

...

Keyword(s):

Drosophila Melanogaster ◽

Differential Expression ◽

Hox Genes ◽

Expression Profiles ◽

Fruit Fly ◽

Insect Species ◽

Wing Morphology ◽

Hox Proteins ◽

Spatial Expression ◽

Flying Insects

AbstractFlying insects have invaded all the aerial space on Earth and this astonishing radiation could not have been possible without a remarkable morphological diversification of their flight appendages. Here, we show that characteristic spatial expression profiles and levels of the Hox genes Antennapedia (Antp) and Ultrabithorax (Ubx) underlie the formation of two different flight organs in the fruit fly Drosophila melanogaster. We further demonstrate that flight appendage morphology is dependent on specific Hox doses. Interestingly, we find that wing morphology from evolutionary distant four-winged insect species is also associated with a differential expression of Antp and Ubx. We propose that variation in the spatial expression profile and dosage of Hox proteins is a major determinant of flight appendage diversification in Drosophila and possibly in other insect species during evolution.

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