Monarch butterflies reared under autumn‐like conditions have more efficient flight and lower post‐flight metabolism

Abstract

1. Many migratory animals undergo physiological and behavioural changes to prepare for and sustain long‐distance movements. Because insect migrations are common and diverse, studies that examine how migratory insects meet the energetic demands of long‐distance movements are badly needed. 2. Monarch butterflies (Danaus plexippus) migrate up to 4000 km annually from eastern North America to wintering sites in central Mexico. Autumn generation monarchs undergo physiological and behavioural changes in response to environmental cues to initiate migration. In particular, exposure to cooler temperatures and shorter day lengths in early autumn causes monarchs to enter the hormonally induced state of reproductive diapause. 3. This study examined differences in flight‐associated metabolic rate (MR) and flight performance metrics for monarchs experimentally reared under autumn‐like conditions (typically experienced before the southward migration) relative to monarchs reared under summer‐like conditions. 4. Adult monarchs reared under autumn‐like conditions showed lower post‐flight MRs, greater flight efficiency, and lower measures of reproductive activity relative to monarchs reared under summer‐like conditions. Increases in post‐flight metabolism were associated with monarch body weight, age, and flight velocity. 5. These findings suggest that a trans‐generational shift in flight energetics is an important component of the monarch's complex migratory syndrome, and that physiological changes that accompany reproductive diapause facilitate energy conservation during flight.

Locust density shapes energy metabolism and oxidative stress resulting in divergence of flight traits

“…1 H ). Based on average flight speed and flight muscle mass, flight kinetic energy was generated ( 28 ). Solitary locusts showed significantly higher flight muscle kinetic energy at time points within 0.25 h. During longer flight tests (over 0.25 h) there was no significant difference between gregarious and solitary locusts ( Fig.…”

“…Based on the mass and flight data, we estimated the flight kinetic energy (KE) during flight process as KE = 1/2 × mass × velocity 2 (joules) ( 28 ). Flight muscle mass was determined indirectly by cutting the thorax (shorn of legs) and removing trace nonmuscular features such as fats and components of the digestive tract.…”

Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies

“…We measured monarch flight indoors during May-June 2018 using a tethered flight mill (see Figure S1 for schematic) in a 9 m 2 room at 29.7 • C (range 27.8-31.4 • C) between 1000 and 1730 h. Five to six days post-eclosion, we glued lightweight steel wires (15 lb test) to the dorsal side of each monarchs' thorax using rubber cement, following Bradley and Altizer [58]. As per Schroeder et al [59], the average mass of the wire attachment was 0.19 g (range 0.10-0.33 g). Monarchs were placed into 0.6 m 3 mesh cages to adjust to the weight of the wire, with 20% honey-water provided ad libitum).…”

Sex-related interannual plasticity in wing morphological design in Heliconius charithonia enhances flight metabolic performance

“…Post-flight metabolic rate (PFMR). Since it was not possible to measure actual flight metabolic rate in H. charithonia we assessed post-flight metabolic rate as estimator of the metabolic cost of flight activity after a brief flight [46,47]. The day following measurement of the RMR, each individual was selected randomly and placed in a new polyester cylindrical mesh cage (70 x 120 cm), in which the butterfly was forced to fly continuously for a period of 90 seconds preventing them from landing by blowing short bursts of air with a manual pump if necessary.…”

“…As an estimator of the PFMR, the integral of the effort was used (i.e. total CO 2 production from the second minute of post-activity up until seven minutes were completed within the chamber of the respirometer [50], as well as the PFMR maximum (PFMRmax; average of the second minute of CO 2 production) [46].…”