Olle Lindestad is currently a Ph.D. student in the Department of Zoology, Stockholm University. Olle will be defending his thesis this February. In this insight, Olle discusses with us his article “Variation in butterfly diapause duration in relation to volitinism suggests adaptation to autumn warmth, not winter cold”, how his interest in ecology was shaped, as well as his interests outside of research.
What’s your paper about?
We have used common-garden rearing and respirometry to measure the duration of diapause in butterfly pupae from different populations. Diapause is a resting state in which most temperate insects spend winter; during diapause, development toward adulthood is put on pause, and metabolic rate is greatly reduced. For many insects, an individual will leave diapause and become ready to resume development when some kind of internal biological “timer” has counted down. Populations of the same species often differ across geographic clines in the length of this “timer”, so that diapause intrinsically lasts longer for some populations than others. This could help insects adapt to different local climates (e.g. a longer or shorter winter), but the geographic pattern is often completely different for different species (sometimes longer winters correlate with a longer diapause; sometimes the opposite) which makes it difficult to infer precisely what climatic factors the insect populations have adapted to.
How did you come up with the idea for it?
This study is part of a larger research project concerned with how and why insect populations differ in their voltinism—the number of generations produced per year. We’d previously found that populations of the speckled wood butterfly, located within only 50-100 km of one another but differing somewhat in their local climate, differ in how they use daylength signals during larval development to control the number of generations produced (one generation/year in places where winter is long and summer short; two generations/year in places where summer is somewhat longer). This local adaptation includes differences in when diapause is initiated. Because of this, we were curious about whether these populations also differed genetically in how they behave once diapause is in progress. For example, breaking diapause early in the spring could be an adaptation that allows an extra generation to be fitted into the available growing season; this hypothesis would predict that populations experiencing short winters should also evolve an intrinsically shorter diapause. However, this is not at all what we found! Although populations did vary in the duration of diapause, they all appear to end their diapause so early that it shouldn’t differentially affect the timing of emergence in the spring.
What are the key messages of your article?
An idea that our results seem to support, and that we believe can help make sense of results across other insect species as well, is that variation in diapause duration is less tied to the length of winter as such and more tied to exposure to autumn warmth. Diapause can be understood as a way for insects to prevent developing too early. As autumn moves into winter, at a certain point the weather becomes cold enough that development is prevented simply by low temperatures; an insect can safely exit diapause at this point, and development will not resume until spring warmth arrives. True to this idea, when we estimated the time points at which diapause is initiated versus when winter cold arrives in nature, the lab-measured diapause durations for each butterfly population matched these values very well. Variation in the yearly number of generations complicates these optimal diapause durations. In some cases, extending the intrinsic duration of diapause or adding an additional generation can in fact be seen as two different solutions to the same problem of synchronizing development with the seasonal cycle.
Did you have any problems setting up the experiment/gathering your data?
We actually had to scrap the entire experiment and re-run it the following year. It turned out that hundreds of our butterfly pupae had in fact not entered diapause, as a result of one of the larval rearing cabinets being wrongly programmed (through human or machine error? We may never know). But I can’t be bitter about this, because when re-running the experiment for what ultimately became this paper, we also took the opportunity to modify the methods somewhat. The population differences discussed in the paper would not have been as clearly visible using our original design.
How did you get involved in ecology?
During my first year at university, it became clear that the parts of biology that excited me the most were those where organisms were considered in their natural context; I find the interplay between species and their environment endlessly fascinating. So for elective courses and degree projects, I sought out these kinds of subjects. My bachelor’s, master’s and PhD thesis projects have all dealt with quite different organisms (tick-borne bacteria; grasses; butterflies), but all of them have explored ecological questions. I was especially happy to get the chance to work with insects for my PhD project, as the tiny but dramatic world they inhabit has always been especially close to my heart.
What do you do in your spare time?
I draw comics, grow potatoes on my balcony, and am active in the climate protest movement.
Your can read Olle’s paper here