Directional selection on cold tolerance does not constrain plastic capacity in a butterfly

Kristin Franke,Klaus Fischer,Anneke Dierks

doi:10.1186/1471-2148-12-235

Abstract

BackgroundOrganisms may respond to environmental change by means of genetic adaptation, phenotypic plasticity or both, which may result in genotype-environment interactions (G x E) if genotypes differ in their phenotypic response. We here specifically target the latter source of variation (i.e. G x E) by comparing plastic responses among lines of the tropical butterfly Bicyclus anynana that had been selected for increased cold tolerance and according controls. Our main aim here was to test the hypothesis that directional selection on cold tolerance will interfere with plastic capacities.ResultsPlastic responses to temperature and feeding treatments were strong, with e.g. higher compared to lower temperatures reducing cold tolerance, longevity, pupal mass, and development time. We report a number of statistically significant genotype-environment interactions (i.e. interactions between selection regime and environmental variables), but most of these were not consistent across treatment groups. We found some evidence though for larger plastic responses to different rearing temperatures in the selection compared to the control lines, while plastic responses to different adult temperatures and feeding treatments were overall very similar across selection regimes.ConclusionOur results indicate that plastic capacities are not always constrained by directional selection (on cold tolerance) and therefore genetic changes in trait means, but may operate independently.

Highlights

Organisms may respond to environmental change by means of genetic adaptation, phenotypic plasticity or both, which may result in genotype-environment interactions (G x E) if genotypes differ in their phenotypic response
At the higher rearing temperature, larval time was longer in the control compared to the inbred groups (C: 28.0 ± 0.08 d > inbreeding 1 (I1): 27.1 ± 0.08 d = inbreeding 2 (I2): 27.1 ± 0.08 d), while there were no significant differences at 20°C (C: 50.5 ± 0.1 d = I1: 50.3 ± 0.1 d = I2: 50.9 ± 0.1 d; Tukey HSD; significant inbreeding level * rearing temperature interaction)
Regarding effects of temperature, feeding treatment, sex, inbreeding and selection regime our results are in good agreement with the hypotheses outlined in Table 1 and with earlier findings obtained in B. anynana and other insects

Summary

Introduction

Organisms may respond to environmental change by means of genetic adaptation, phenotypic plasticity or both, which may result in genotype-environment interactions (G x E) if genotypes differ in their phenotypic response. Enhanced resistance to temperature stress can be reached by means of phenotypic plasticity, i.e. nongenetic physiological changes as a direct response to environmental variation, or genetic adaptation [5,8]. High-altitude populations typically show a lower heat but a higher cold tolerance than low-altitude populations [14]. Such geographic variation in fitness-related traits provides strong evidence that these patterns have been shaped by natural selection [14,15]. Several species are known to respond readily to artificial selection on thermal tolerance traits, providing direct experimental proof for genetic adaptation in temperature stress resistance Several species are known to respond readily to artificial selection on thermal tolerance traits, providing direct experimental proof for genetic adaptation in temperature stress resistance (e.g. [2,16,17])

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Discussion

Conclusion