On the fate of seasonally plastic traits in a rainforest butterfly under relaxed selection
Oostra, V. ; Brakefield, P.M. ; Hiltemann, Y. ; Zwaan, B.J. ; Brattström, O. - \ 2014
Ecology and Evolution 4 (2014)13. - ISSN 2045-7758 - p. 2654 - 2667.
sexual size dimorphism - bicyclus-anynana - phenotypic plasticity - reaction norms - life-history - evolutionary significance - artificial selection - geographic-variation - resource-allocation - thermal plasticity
Many organisms display phenotypic plasticity as adaptation to seasonal environmental fluctuations. Often, such seasonal responses entails plasticity of a whole suite of morphological and life-history traits that together contribute to the adaptive phenotypes in the alternative environments. While phenotypic plasticity in general is a well-studied phenomenon, little is known about the evolutionary fate of plastic responses if natural selection on plasticity is relaxed. Here, we study whether the presumed ancestral seasonal plasticity of the rainforest butterfly Bicyclus sanaos (Fabricius, 1793) is still retained despite the fact that this species inhabits an environmentally stable habitat. Being exposed to an atypical range of temperatures in the laboratory revealed hidden reaction norms for several traits, including wing pattern. In contrast, reproductive body allocation has lost the plastic response. In the savannah butterfly, B. anynana (Butler, 1879), these traits show strong developmental plasticity as an adaptation to the contrasting environments of its seasonal habitat and they are coordinated via a common developmental hormonal system. Our results for B. sanaos indicate that such integration of plastic traits – as a result of past selection on expressing a coordinated environmental response – can be broken when the optimal reaction norms for those traits diverge in a new environment
Quantitative genetic analysis of responses to larval food limitation in a polyphenic butterfly indicates environment- and trait-specific effects
Saastamoinen, M. ; Brommer, J.E. ; Brakefield, P.M. ; Zwaan, B.J. - \ 2013
Ecology and Evolution 3 (2013)10. - ISSN 2045-7758 - p. 3576 - 3589.
bicyclus-anynana - phenotypic plasticity - life-history - adaptive responses - reaction norms - evolution - growth - genotype - evolvability - canalization
Different components of heritability, including genetic variance (VG), are influenced by environmental conditions. Here, we assessed phenotypic responses of life-history traits to two different developmental conditions, temperature and food limitation. The former represents an environment that defines seasonal polyphenism in our study organism, the tropical butterfly Bicyclus anynana, whereas the latter represents a more unpredictable environment. We quantified heritabilities using restricted maximum likelihood (REML) procedures within an “Information Theoretical” framework in a full-sib design. Whereas development time, pupal mass, and resting metabolic rate showed no genotype-by-environment interaction for genetic variation, for thorax ratio and fat percentage the heritability increased under the cool temperature, dry season environment. Additionally, for fat percentage heritability estimates increased under food limitation. Hence, the traits most intimately related to polyphenism in B. anynana show the most environmental-specific heritabilities as well as some indication of cross-environmental genetic correlations. This may reflect a footprint of natural selection and our future research is aimed to uncover the genes and processes involved in this through studying season and condition-dependent gene expression
Translating environmental gradients into discontinuous reaction norms via hormone signalling in a polyphenic butterfly
Oostra, V. ; Jong, M.A. de; Invergo, B.M. ; Kesbeke, F. ; Wende, F. ; Brakefield, P.M. ; Zwaan, B.J. - \ 2011
Proceedings of the Royal Society. B: Biological Sciences 278 (2011)1706. - ISSN 0962-8452 - p. 789 - 797.
bicyclus-anynana - phenotypic plasticity - developmental plasticity - drosophila-melanogaster - starvation resistance - artificial selection - eyespot size - evolution - responses - canalization
Polyphenisms—the expression of discrete phenotypic morphs in response to environmental variation—are examples of phenotypic plasticity that may potentially be adaptive in the face of predictable environmental heterogeneity. In the butterfly Bicyclus anynana, we examine the hormonal regulation of phenotypic plasticity that involves divergent developmental trajectories into distinct adult morphs for a suite of traits as an adaptation to contrasting seasonal environments. This polyphenism is induced by temperature during development and mediated by ecdysteroid hormones. We reared larvae at separate temperatures spanning the natural range of seasonal environments and measured reaction norms for ecdysteroids, juvenile hormones (JHs) and adult fitness traits. Timing of peak ecdysteroid, but not JH titres, showed a binary response to the linear temperature gradient. Several adult traits (e.g. relative abdomen mass) responded in a similar, dimorphic manner, while others (e.g. wing pattern) showed a linear response. This study demonstrates that hormone dynamics can translate a linear environmental gradient into a discrete signal and, thus, that polyphenic differences between adult morphs can already be programmed at the stage of hormone signalling during development. The range of phenotypic responses observed within the suite of traits indicates both shared regulation and independent, trait-specific sensitivity to the hormone signal.
Quantitative genetic variation in an island population of the speckled wood butterfly (Pararge aegeria)
Windig, J.J. ; Veerkamp, R.F. ; Nylin, S. - \ 2004
Heredity 93 (2004)5. - ISSN 0018-067X - p. 450 - 454.
sexual size dimorphism - bicyclus-anynana - fluctuating asymmetry - inbreeding depression - evolutionary genetics - natural-selection - reaction norms - wing pattern - trade-offs - inachis-io
Evidence of changes in levels of genetic variation in the field is scarce. Theoretically, selection and a bottleneck may lead to the depletion of additive genetic variance (VA) but not of nonadditive, dominance variance (VD), although a bottleneck may converse VD to V A. Here we analyse quantitative genetic variation for the Speckled Wood butterfly Pararge aegeria on the island of Madeira about 120 generations after first colonisation. Colonisation of the island involved both a bottleneck and strong natural selection, changing the average value of traits. Several life history and morphological traits with varying levels of change since colonisation were analysed. In accordance with expectations, all traits except one showed relatively low levels of VA, with an average heritability (h2) of 0.078. Levels of VD for these traits were relatively high, 20-94% of total variance and on average 80% of VG. The exception was a morphological trait that probably had not experienced strong natural selection after colonisation, for which a h2 of 0.27 was found. Another interesting observation is that the population seems resistant to inbreeding effects, which may be the result of purging of deleterious alleles.