Abstract
Reproductive diapause is a primary mechanism used by arthropods to synchronize their life cycle with seasonal changes in temperate regions. Our study species, Drosophila montana, represents the northern insect species where flies enter reproductive diapause under short day conditions and where the precise timing of diapause is crucial for both survival and offspring production. We have studied clinal variation in the critical day length for female diapause induction (CDL) and their overall susceptibility to enter diapause (diapause incidence), as well as the temperature sensitivity of these traits. The study was performed using multiple strains from four latitudinal clines of the species – short clines in Finland and Alaska and long clines in the Rocky Mountains and the western coast of North America – and from one population in Kamchatka, Russia. CDL showed strong latitudinal clines on both continents, decreasing by one hour per five degrees decline in latitude, on average. CDL also decreased in all populations along with an increase in fly rearing temperature postponing the diapause to later calendar time, the effects of temperature being stronger in southern than in northern population. Female diapause incidence was close to 100% under short day/low temperature conditions in all populations, but decreased below 50% even under short days in 19°C in the southern North American western coast populations and in 22°C in most populations. Comparing a diversity of climatic data for the studied populations showed that while CDL is under a tight photoperiodic regulation linked with latitude, its length depends also on climatic factors determining the growing season length. Overall, the study deepens our understanding of how spatial and environmental parameters affect the seasonal timing of an important biological event, reproductive diapause and helps to estimate the evolutionary potential of insect populations to survive in changing climatic conditions.
Highlights
Species living in seasonally varying environments need to be able to anticipate the arrival of harsh season and have enough time to behaviorally and/or physiologically prepare themselves
photoperiodic response curves (PPRCs) drawn for different cline populations in 13°C, 16°C/17°C and 19°C were based on female diapause incidenses under several LDs, while in 22°C female diapause incidence was measured only in one LD where it had been found to be close to 100% at lower temperatures
Information on the CDLs estimated from the PPRCs of individual strains/populations under different temperatures is available in Supplementary material Appendix 2 Table A4
Summary
Species living in seasonally varying environments need to be able to anticipate the arrival of harsh season and have enough time to behaviorally and/or physiologically prepare themselves In this process the ‘token stimuli’ that do not represent the. In the southern latitudes, where seasonal variation in the day length is small, temperature changes may have a higher predictive value than the photoperiod. In both cases, current climate change may complicate organisms’ ability to adjust their life cycle according to seasonal changes, if the environmental variables that serve as token cues no longer correlate with the environment causing selection (Visser et al 2010). High within-population variation in the timing of reproductive diapause is likely to be beneficial for both sexes in environments, where the length of the warm period varies between years
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