Latitudinal variation in diapause duration and post-winter development in two pierid butterflies in relation to phenological specialization

Abstract

Diapause plays a central role in insect life cycles by allowing survival during adverse seasonal conditions as well as synchronizing life cycles with the period of mate and food availability. Seasonal timing is expected to be particularly important for species that are dependent on resources available during a short time window-so-called phenological specialists-and latitudinal clines in seasonality are expected to favor local adaptation in phenological timing. However, to what degree latitudinal variation in diapause dynamics and post-winter development due to such local adaptation is influenced by the degree of phenological specialization is not well known. We experimentally studied two pierid butterfly species and found that the phenological specialist Anthocharis cardamines had shorter diapause duration than the phenological generalist Pieris napi along a latitudinal gradient in Sweden. Moreover, diapause duration increased with latitude in P. napi but not in A. cardamines. Sensitivity of the two species to winter thermal conditions also differed; additional cold temperature during the winter period shortened diapause duration for P. napi pupae but not for A. cardamines pupae. In both species, post-winter pupal development was faster after longer periods of cold conditions, and more southern populations developed faster than northern populations. Post-winter development was also invariably faster at higher temperatures in both species. We argue that the observed differences in diapause dynamics between the two species might be explained by the difference in phenological specialization that influences the costs of breaking diapause too early in the season.

Energy and lipid metabolism during direct and diapause development in a pierid butterfly

“…The results also suggest that the maximal diapause duration is likely to be under 12 months in the field and are in line with previous data on the same population (Posledovich et al, 2015). Endogenous diapause is important as it decreases the risk of early emergence as a result of heat spells during autumn and early winter months (Danks, 2007).…”

“…Pupae were kept for 2, 4, 6 or 12 months at 2°C before being moved to 20°C. According to previous research (Posledovich et al, 2015), the 2 month point should precede diapause termination, while the 4 month and later time points should represent post-termination where development has probably already resumed. Pupae were weighed to the nearest 0.1 mg (Sauter RE1614) and placed individually into 20 ml syringes that acted as respirometry chambers throughout the experiment.…”

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

“…3A and D), in agreement with previous results from Swedish populations that included an overlapping winter duration treatment of 90 days (Posledovich et al. 2015). The time showed a steep decline with increasing duration of cold; there was approximately a halving of the time spent in post‐winter development from 60 days to 120 days in cold.…”

“…2014), but the studies that have looked at winter temperatures did not find any effect (Sparks and Yates 1997; Posledovich et al. 2015). However, Posledovich et al.…”

“…However, Posledovich et al. (2015) found an effect of winter duration for Swedish A. cardamines , in the form of an increased post‐winter development rate ( r P ) between 90 and 150 days of winter duration treatment. Here, we have focused on shorter winter durations, from 30 to 120 days, which should be ecologically relevant for UK populations, and we have compared UK and Swedish populations.…”