Longer and warmer prewinter periods reduce post‐winter fitness in a diapausing insect

Abstract

Diapause is considered an important adaptation for survival of winter; however, insects often enter diapause long before its onset. Thus, diapausing insects must also be able to survive these prewinter conditions which warm temperatures could make quite energetically taxing despite relative inactivity. We tested for both immediate and delayed fitness effects of prewinter conditions in diapausing Pieris napi butterfly pupae, experimentally exposing them to different prewinter treatments in a factorial design. We placed diapausing pupae at one of three temperatures (15, 20 and 25°C) for 1 to 16 weeks, followed by the same standardized winter for all individuals. We monitored survival of pupae at multiple points during the experiment, including after winter, as well as their change in mass. For a subset of individuals, we also made repeated metabolic measurements. We found substantial weight loss during prewinter warm periods, greater during longer prewinter treatments at higher temperatures. This weight loss was associated with elevated metabolic rates at higher temperatures which increased over the duration of the prewinter treatment. Although we found little prewinter mortality associated with these conditions, mortality was much greater post‐winter for individuals in long, warm prewinter treatments and the dry mass of adults that did survive these conditions was lower, highlighting the need to understand chronic or delayed effects of stress on fitness. Ultimately, we found substantial fitness consequences of prewinter conditions for a diapausing insect. Given that climate change will make these prewinter periods both longer and more intense, it will be important to understand how dormant organisms tolerate or reduce the length of these dormant, inactive periods. Read the free Plain Language Summary for this article on the Journal blog.

Ecological and life‐history traits predict temporal trends in biomass of boreal moths

“…However, increase in voltinism is maladaptive if environmental change results in emergence of extra generations so late in the season that overwinter survival fails (Blackshaw & Esbjerg, 2018; Pöyry et al, 2011; Van Dyck et al, 2014). Species overwintering as a pupa are vulnerable to extension of the warm period in the end of summer and autumn (Nielsen et al, 2022), and this may hold for egg‐overwinterers too. Our results suggest that egg‐ and adult‐overwinterers are smaller in southern than northern Finland.…”

“…Duration and temperature of the growing season determine the physiological time available for insect growth and development and the number of generations appearing per year (i.e., voltinism) (Kivelä et al, 2013(Kivelä et al, , 2016Pöyry et al, 2011), which affects abundance. In addition to conditions during the growing season, winter conditions likely affect insect abundance in boreal environments too, both through cold mortality (Leather et al, 1993) and increased energy expenditure during diapause due to climate warming (Bosch et al, 2010;Nielsen et al, 2022). All resident species living in the boreal region are adapted to winter conditions, but overwinter survival may be compromised under exceptional winters (Abarca et al, 2019).…”

Microclimatic variation affects developmental phenology, synchrony and voltinism in an insect population

“…Additionally, individuals that enter diapause relatively early in the season (all predominantly univoltine sites in e.g. Figure 6) have blocked their ability to move around, eat and accumulate resources, while they at the same time risk depleting their resources before winter as they enter diapause when temperatures are still high (Irwin & Lee, 2003; Nielsen et al, 2022; Williams et al, 2012). On the other hand, the decision to not go into diapause and instead develop directly in the late season will most likely lead to death before reproduction can occur, since diapause is crucial to cope with cold conditions (Van Dyck et al, 2015).…”

Burrowing depth mediates the extent of metabolic suppression in a soil‐overwintering insect

“…Devlin et al, 2022;Roberts et al, 2021;Williams et al, 2003Williams et al, , 2015. Furthermore, individuals that survive warm winters may suffer negative effects on post-dormancy development, fecundity and survival (Nielsen et al, 2022;Williams et al, 2003). For instance, gall fly (Eurosta solidaginis) larvae that overwinter in cooler, snow-free microhabitats save more energy and have higher survival and potential fecundity than those in warmer, subnivean microclimates (Irwin et al, 2003).…”