Metabolome dynamics of diapause in the butterfly Pieris napi: distinguishing maintenance, termination and post-diapause phases

Abstract

Diapause is a deep resting stage facilitating temporal avoidance of unfavourable environmental conditions, and is used by many insects to adapt their life cycle to seasonal variation. Although considerable work has been invested in trying to understand each of the major diapause stages (induction, maintenance and termination), we know very little about the transitions between stages, especially diapause termination. Understanding diapause termination is crucial for modelling and predicting spring emergence and winter physiology of insects, including many pest insects. In order to gain these insights, we investigated metabolome dynamics across diapause development in pupae of the butterfly , which exhibits adaptive latitudinal variation in the length of endogenous diapause that is uniquely well characterized. By employing a time-series experiment, we show that the whole-body metabolome is highly dynamic throughout diapause and differs between pupae kept at a diapause-terminating (low) temperature and those kept at a diapause-maintaining (high) temperature. We show major physiological transitions through diapause, separate temperature-dependent from temperature-independent processes and identify significant patterns of metabolite accumulation and degradation. Together, the data show that although the general diapause phenotype (suppressed metabolism, increased cold tolerance) is established in a temperature-independent fashion, diapause termination is temperature dependent and requires a cold signal. This revealed several metabolites that are only accumulated under diapause-terminating conditions and degraded in a temperature-unrelated fashion during diapause termination. In conclusion, our findings indicate that some metabolites, in addition to functioning as cryoprotectants, for example, are candidates for having regulatory roles as metabolic clocks or time-keepers during diapause.

Monarch butterflies use an environmentally sensitive, internal timer to control overwintering dynamics

“…Although resolution of both of these properties requires elucidation of a diapause termination mechanism, termination remains poorly understood. Lehmann et al () outlined particular challenges of studying termination that are primarily a result of the complex interaction of environment and internal physiological control. By studying a combination of different source populations in different environmental chamber conditions over time, we were able to modularize individual components of termination and identify molecular controllers of specific termination processes.…”

“…Accumulation of small molecule cryoprotectants (e.g., sorbitol, alanine, etc) in response to cold exposure has been observed in diapause and implicated in diapause termination in other insects (e.g., Leal et al, 2018;Lehmann et al, 2018;Michaud & Denlinger, 2007;Wang, Egi, Takeda, Oishi, & Sakamoto, 2014). Calcium signalling mediates osmotic stress due to small molecule cryoprotectant accumulation in insects (Storey, 1990).…”

Termination of pupal diapause in the pine processionary moth Thaumetopoea pityocampa

“…Visually determining the timing of diapause termination is difficult or impossible. Therefore, investigating the physiological processes throughout diapause could repreent a pragmatic approach for determining and understanding its termination in insects (Soula & Menu, 2005;Sgolastra et al, 2010;Lehmann et al, 2018).…”

Developmental plasticity in metabolism but not in energy reserve accumulation in a seasonally polyphenic butterfly

“…These physiological differences culminate in the life stage that is capable of entering diapause, because surviving a long adverse period in the dormant state of diapause necessitates a very different physiology compared to direct development into reproductive adult (e.g. Han and Bauce, 1998; Hahn and Denlinger, 2007, 2011; Liu et al, 2007, 2016; Rozsypal et al, 2013; Lehmann et al, 2016, 2018).…”

“…Besides metabolic rate, the diapause and direct development pathways are expected to show also other pre-diapause physiological differences. Overwinter survival necessitates energy reserves that can fuel metabolism through the whole dormant period during which feeding is either not possible at all or insufficient to fully fuel metabolism (Tauber et al, 1986; Danks, 1987; Hahn and Denlinger, 2007, 2011; Lehmann et al, 2016, 2018; see Liu et al, 2016 for energy reserves for summer diapause). These energy reserves must be accumulated before the beginning of diapause, which may result in differences between pathways in the allocation of resources to building reserves (Tauber et al, 1986; Danks, 1987; Hahn and Denlinger, 2007, 2011; Liu et al, 2007).…”