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Asymmetric life-history decision-making in butterfly larvae.

Friberg M, Aalberg Haugen IM, Dahlerus J, Gotthard K, Wiklund C - Oecologia (2010)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Stockholm University, Stockholm, Sweden. magne.friberg@zoologi.su.se

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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Comparison of the asymmetric ability to change pathway to fit the new environment between larvae transferred from a diapause-inducing condition (short daylength) into an environment that triggers direct development (long daylength) (filled squares) and larvae transferred in the opposite direction (open circles) in aP. napi, bA. levana and cP. aegeria. Data shown are the proportions of larvae (± binomial 95% CI) that managed to adjust to the new environment when transferred between environments in the penultimate and ultimate larval instars
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Fig1: Comparison of the asymmetric ability to change pathway to fit the new environment between larvae transferred from a diapause-inducing condition (short daylength) into an environment that triggers direct development (long daylength) (filled squares) and larvae transferred in the opposite direction (open circles) in aP. napi, bA. levana and cP. aegeria. Data shown are the proportions of larvae (± binomial 95% CI) that managed to adjust to the new environment when transferred between environments in the penultimate and ultimate larval instars

Mentions: Pieris napi larvae of both sexes (Table 1) behaved similarly in both replicates, and the pathway decision was strongly dependent on the timing of the transfer between cabinets (Table 1). Larvae that were transferred to their final cabinet as eggs or in instars I–III typically followed the larval pathway triggered in that final cabinet, as did the majority of larvae transferred in instar IV (Table 1). Larvae that were transferred in instar V typically did not switch their developmental response in accordance with the new daylength to which they had been transferred (Table 1). There was no difference in the ability to adjust to the new environment between the different sexes (χ12 = 0.36, P = 0.85) or replicates (χ12 = 0.81, P = 0.37), and these factors were thus removed from the model. Instead, the larval potential to respond to the new daylength depended on the transfer direction, and larvae that came from a long daylength into a short daylength were typically more reluctant to respond to the new environment by entering diapause development. By contrast, most larvae that were moved from the short to the long daylength in the penultimate instar switched pathways and entered direct development, and a substantial fraction (39%) were able to adjust their decision to the new daylength when the transfer took place as late as in the last instar (instar moved χ12 = 95.3, P < 0.001; transfer direction χ12 = 22.4, P < 0.001; all interactions were nonsignificant and removed from the model; Fig. 1a).Fig. 1


Asymmetric life-history decision-making in butterfly larvae.

Friberg M, Aalberg Haugen IM, Dahlerus J, Gotthard K, Wiklund C - Oecologia (2010)

Comparison of the asymmetric ability to change pathway to fit the new environment between larvae transferred from a diapause-inducing condition (short daylength) into an environment that triggers direct development (long daylength) (filled squares) and larvae transferred in the opposite direction (open circles) in aP. napi, bA. levana and cP. aegeria. Data shown are the proportions of larvae (± binomial 95% CI) that managed to adjust to the new environment when transferred between environments in the penultimate and ultimate larval instars
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3021710&req=5

Fig1: Comparison of the asymmetric ability to change pathway to fit the new environment between larvae transferred from a diapause-inducing condition (short daylength) into an environment that triggers direct development (long daylength) (filled squares) and larvae transferred in the opposite direction (open circles) in aP. napi, bA. levana and cP. aegeria. Data shown are the proportions of larvae (± binomial 95% CI) that managed to adjust to the new environment when transferred between environments in the penultimate and ultimate larval instars
Mentions: Pieris napi larvae of both sexes (Table 1) behaved similarly in both replicates, and the pathway decision was strongly dependent on the timing of the transfer between cabinets (Table 1). Larvae that were transferred to their final cabinet as eggs or in instars I–III typically followed the larval pathway triggered in that final cabinet, as did the majority of larvae transferred in instar IV (Table 1). Larvae that were transferred in instar V typically did not switch their developmental response in accordance with the new daylength to which they had been transferred (Table 1). There was no difference in the ability to adjust to the new environment between the different sexes (χ12 = 0.36, P = 0.85) or replicates (χ12 = 0.81, P = 0.37), and these factors were thus removed from the model. Instead, the larval potential to respond to the new daylength depended on the transfer direction, and larvae that came from a long daylength into a short daylength were typically more reluctant to respond to the new environment by entering diapause development. By contrast, most larvae that were moved from the short to the long daylength in the penultimate instar switched pathways and entered direct development, and a substantial fraction (39%) were able to adjust their decision to the new daylength when the transfer took place as late as in the last instar (instar moved χ12 = 95.3, P < 0.001; transfer direction χ12 = 22.4, P < 0.001; all interactions were nonsignificant and removed from the model; Fig. 1a).Fig. 1

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, Stockholm University, Stockholm, Sweden. magne.friberg@zoologi.su.se

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.

Show MeSH