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
Ecdysteroid hormones link the juvenile environment to alternative adult life histories in a seasonal insect
Oostra, V. ; Mateus, A.R.A. ; Burg, K.R.L. van den; Piessens, T. ; Eijk, M. van; Brakefield, P.M. ; Beldade, P. ; Zwaan, B.J. - \ 2014
American Naturalist 184 (2014)3. - ISSN 0003-0147 - p. E79 - E92.
butterfly bicyclus-anynana - drosophila-melanogaster - phenotypic plasticity - developmental temperature - adaptive responses - thermal plasticity - wing pattern - lepidoptera - diapause - nymphalidae
The conditional expression of alternative life strategies is a widespread feature of animal life and a pivotal adaptation to life in seasonal environments. To optimally match suites of traits to seasonally changing ecological opportunities, animals living in seasonal environments need mechanisms linking information on environmental quality to resource allocation decisions. The butterfly Bicyclus anynana expresses alternative adult life histories in the alternating wet and dry seasons of its habitat as endpoints of divergent developmental pathways triggered by seasonal variation in preadult temperature. Pupal ecdysteroid hormone titers are correlated with the seasonal environment, but whether they play a functional role in coordinating the coupling of adult traits in the alternative life histories is unknown. Here, we show that manipulating pupal ecdysteroid levels is sufficient to mimic in direction and magnitude the shifts in adult reproductive resource allocation normally induced by seasonal temperature. Crucially, this allocation shift is accompanied by changes in ecologically relevant traits, including timing of reproduction, life span, and starvation resistance. Together, our results support a functional role for ecdysteroids during development in mediating strategic reproductive investment decisions in response to predictive indicators of environmental quality. This study provides a physiological mechanism for adaptive developmental plasticity, allowing organisms to cope with variable environments