Asymmetric life-history decision-making in butterfly larvae |
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Authors: | Magne Friberg Inger M Aalberg Haugen Josefin Dahlerus Karl Gotthard Christer Wiklund |
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Institution: | (1) Department of Zoology, Stockholm University, 10691 Stockholm, Sweden |
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Abstract: | In temperate environments, insects appearing in several generations in the growth season typically have to decide during the
larval period whether to develop into adulthood, or to postpone adult emergence until next season by entering a species-specific
diapause stage. This decision is typically guided by environmental cues experienced during development. An early decision
makes it possible to adjust growth rate, which would allow the growing larva to respond to time stress involved in direct
development, whereas a last-minute decision would instead allow the larva to use up-to-date information about which developmental
pathway is the most favourable under the current circumstances. We study the timing of the larval pathway decision-making
between entering pupal winter diapause and direct development in three distantly related butterflies (Pieris napi, Araschnia levana and Pararge aegeria). We pinpoint the timing of the larval diapause decision by transferring larvae from first to last instars from long daylength
(inducing direct development) to short daylength conditions (inducing diapause), and vice versa. Results show that the pathway
decision is typically made in the late instars in all three species, and that the ability to switch developmental pathway
late in juvenile life is conditional; larvae more freely switched from diapause to direct development than in the opposite
direction. We contend that this asymmetry is influenced by the additional physiological preparations needed to survive the
long and cold winter period, and that the reluctance to make a late decision to enter diapause has the potential to be a general
trait among temperate insects. |
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