Effect of winter cold duration on spring phenology of the orange tip butterfly, Anthocharis cardamines

Abstract

The effect of spring temperature on spring phenology is well understood in a wide range of taxa. However, studies on how winter conditions may affect spring phenology are underrepresented. Previous work on Anthocharis cardamines (orange tip butterfly) has shown population-specific reaction norms of spring development in relation to spring temperature and a speeding up of post-winter development with longer winter durations. In this experiment, we examined the effects of a greater and ecologically relevant range of winter durations on post-winter pupal development of A. cardamines of two populations from the United Kingdom and two from Sweden. By analyzing pupal weight loss and metabolic rate, we were able to separate the overall post-winter pupal development into diapause duration and post-diapause development. We found differences in the duration of cold needed to break diapause among populations, with the southern UK population requiring a shorter duration than the other populations. We also found that the overall post-winter pupal development time, following removal from winter cold, was negatively related to cold duration, through a combined effect of cold duration on diapause duration and on post-diapause development time. Longer cold durations also lead to higher population synchrony in hatching. For current winter durations in the field, the A. cardamines population of southern UK could have a reduced development rate and lower synchrony in emergence because of short winters. With future climate change, this might become an issue also for other populations. Differences in winter conditions in the field among these four populations are large enough to have driven local adaptation of characteristics controlling spring phenology in response to winter duration. The observed phenology of these populations depends on a combination of winter and spring temperatures; thus, both must be taken into account for accurate predictions of phenology.

Keywords: Chill duration effects; diapause; insect phenology; local adaptation; post‐diapause development; post‐winter development; respirometry.

Figure 1

Anthocharis cardamines resting on one of its preferred host plant species Cardamine pratensis. Photographer: Sandra Stålhandske.

Figure 2

Temperature profiles for four localities in the United Kingdom and Sweden. Solid lines are mean temperatures for the years 2000–2009 (from the E‐OBS database). The transparent areas show the ranges of the average minimum and maximum temperatures over the same time period.

Figure 3

Effect of cold duration on post‐winter development. Error bars show the 95% confidence interval of the mean. (A, D) Effect of cold duration on development time from removal from winter conditions to hatching for the four populations. (B, E) Effect of cold duration on the time to development initiation following introduction to spring conditions. (C, F) Effect of cold duration on the time in post‐diapause development.

Figure 4

Example of weight loss and respiration of an individual from the 60‐day cold treatment (top row) and an individual from the 150‐day cold treatment (bottom row). (A, C) Weight (gray) and mass corrected CO ₂ production (blue) from day of introduction to warm treatment until hatching. (B, D) Mass corrected CO ₂ production per 45 min cycle. 22–24 cycles were measured overnight. Here, each cycle is represented as a point on the graph. Dashed vertical lines show estimation of termination of diapause based on weight loss. Solid gray line shows cut‐off weight loss slope for diapause termination.