Defining behavioral and molecular differences between summer and migratory monarch butterflies

Abstract

Background: In the fall, Eastern North American monarch butterflies (Danaus plexippus) undergo a magnificent long-range migration. In contrast to spring and summer butterflies, fall migrants are juvenile hormone deficient, which leads to reproductive arrest and increased longevity. Migrants also use a time-compensated sun compass to help them navigate in the south/southwesterly direction en route for Mexico. Central issues in this area are defining the relationship between juvenile hormone status and oriented flight, critical features that differentiate summer monarchs from fall migrants, and identifying molecular correlates of behavioral state.

Neural Integration Underlying a Time-Compensated Sun Compass in the Migratory Monarch Butterfly

“…Throughout this journey monarchs constantly correct their flight direction to maintain a southerly orientation. Laboratory observations from a flight simulator, capable of tracking flight direction, show that migrant monarchs orient towards the southwest (SW) direction by visual cues, relying primarily on the horizontal (azimuthal) position of the sun (Mouritsen & Frost 2002; Froy et al 2003; Zhu et al 2009; Merlin et al 2009; Guerra et al 2012). Migrants use their circadian clocks to compensate for the changing sun position and thereby maintain a fixed flight bearing.…”

Intra- and inter-individual variations in flight direction in a migratory butterfly co-vary with individual mobility

“…This investigation is even more challenging for species with multi-generational migration patterns such as migrant butterflies [e.g. the large white Pieris brassicae (Spieth et al, 1998), the Monarch Danaus plexippus (Zhu et al, 2009) and the painted lady butterfly Vanessa cardui (Stefanescu et al, 2013)] especially when only a part of the population migrates [e.g. P. brassicae (Feltwell, 1982)].…”

Sensory basis of lepidopteran migration: focus on the monarch butterfly

“…Clock-shift experiments testing aspects of the sun compass used by monarchs supports the dominant position of the sun compass and the secondary nature of the magnetic compass in the hierarchy of orientation tools used by monarchs. Clock-shifted migrants will fly in the predicted, adjusted orientation direction during clear, sunny skies, even when the Earth's magnetic field is perceivable and remains unmanipulated [2–5]. During overcast evenings, the magnetic compass may also serve as a backup mechanism for nocturnal lepidopteran migrants that use night sky cues for orientation.…”

“…Recent research has elucidated critical aspects of migration, an evolved behavioral strategy used by several lepidopteran species, including both butterflies (e.g., the North American monarch butterfly, Danaus plexippus [2–7]; the painted lady butterfly, Vanessa cardui [8, 9]) and moths (e.g., the silver Y moth, Autographa gamma [10–12]). To reach their destinations during the migratory journey, migrants likely use either compasses alone or a map and compasses, for navigation [1].…”

“…A map sense allows migrants to know their location relative to their destination, whereas compasses provide migrants with the ability to orient in the proper migratory direction during travel. Although there is debate as to whether or not migrant lepidopterans can possess a map sense (e.g., the monarch; see below), a body of work exists that demonstrates that these species have various and separate compass senses [e.g., 2–7], in which they depend on reliable environmental cues to obtain directional information [13–14]. Having multiple modes for directionality may be advantageous for individuals, because they better inform and fine-tune navigational decision-making during migration.…”