Latest finding - Evolutionary Biology
- How butterflies use hormones to predict the future
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Not only teenagers in their puberty seem to be ruled by hormones. Insects also have hormones that regulate behaviour, growth and reproduction in order to be and do the right thing at the right time. Vicencio Oostra and Maaike de Jong, two PhD students from the Evolutionary Biology lab, just published a paper showing how hormones regulate the adaptation to seasonal variation in the butterfly Bicyclus anynana (Proceedings of the Royal Society B. Online 8 Sep 2010).
- Butterflies living in seasonal environments
In the Evolutionary Biology lab, we study how the tropical butterfly Bicyclus anynana copes with seasonal changes in food availability. During the season of food shortage, reproduction is better postponed rather than giving offspring a poor start in life. Instead, it’s a better strategy to time reproduction to coincide with the season of plentiful food supplies. During development, larvae adjust their metabolism and physiology to match the season in which they expect to emerge as an adult butterfly. In this way, they are well prepared for either food shortage or abundance. In order to anticipate the kind of environment they will emerge in as an adult, it is vital to pick up, during development, relevant signals from the environment indicating the coming change of seasons. In Malawi, this butterfly’s natural habitat, temperature decreases before the onset of the dry season. Larvae use temperature as an indicator for the season that they are in.
- Hormone as switch…
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People from this lab have now discovered that the steroid hormone Ecdysone plays a key role in how, during development, larvae use information from the environment to adjust their adult phenotype to the coming season. In this week’s Proceedings of the Royal Society B they describe how the hormone seems to work as a discrete switch.
- …between wet season or dry season morphs…
If the temperature during larval development remains below a certain threshold –corresponding to the transition to the dry season in the natural environment – Ecdysone is not active until relatively late in development, and the larva develops into a butterfly adapted to the harsh dry season. This butterfly invests relatively little energy in reproduction, but instead invests most energy in body reserves in order to survive this harsh season. If the temperature is above the threshold, Ecdysone is active earlier in development, and the larva develops into a butterfly that invest more energy in early reproduction instead of survival.
- …but only at the relevant temperature
This research shows that already during development there are discrete, hormonal differences between butterflies of the wet and of the dry season. The hormone only switches development between the alternate seasonal morhs at relevant temperature changes that are actually predictive of the transition to the next season.
Oostra V, de Jong MA, Invergo BM, Kesbeke F, Wende F, Brakefield PM and Zwaan BJ. Translating environmental gradients into discontinuous reaction norms via hormone signalling in a polyphenic butterfly. Proceedings of the Royal Society B. Online 8 Sep 2010.
