Latitudinal clines in the timing and temperature‐sensitivity of photoperiodic reproductive diapause in Drosophila montana

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.

Multiple paths to cold tolerance: the role of environmental cues, morphological traits and the circadian clock genevrille

“…However, females’ chill coma resistance (CT min ) showed a significant variation only in D. montana , where it was associated with latitudinally varying temperature (PC2) instead of photoperiod (latitude). Also this association is logical since non-diapausing D. montana females may face quite cold temperatures during the late spring and early autumn in the northern parts of the species distribution [72, 74]. Chill coma recovery time (CCRT) of both species was associated with photoperiod (latitude), as hypothesized.…”

“…1) with raster package v. 2.8-19 [94]. In addition, we obtained growing season length (days) for each site from article by [74] and www.weatherbase.com. Growing season is defined as the average number of days per year when the average daily temperature is at least 5 °C.…”

“…We performed RNAi studies using only the more cold-tolerant D. montana, which has become a model species for studying cold adaption at phenotypic and genetic level (e.g. [63,74,97]). Here, we used females of a mass-bred cage population originating from Seward (Alaska, North America; see in Seward population [74], and thus the females emerging in LD 18:6 can be expected to develop ovaries.…”

“…[63,74,97]). Here, we used females of a mass-bred cage population originating from Seward (Alaska, North America; see in Seward population [74], and thus the females emerging in LD 18:6 can be expected to develop ovaries. After ~4 weeks, we collected newly emerged females (≤ 1 day old) using light CO2 anaesthesia and placed them back in malt-vials into the above-mentioned conditions.…”

Insect photoperiodism: Seasonal development on a revolving planet

“…The fi rst indication of this was provided by Thiele (1977) who showed 'positive' resonance effects (multiple peaks of high diapause incidence in NH experiments) in a strain of the beetle Pterostichus nigrita in Germany (51°N) but 'negative' hourglass-like responses in a strain from Swedish Lapland (64 to 66°N). Hourglass-like NH responses have now been recorded in several species of Drosophila in Finland including D. ezoana (Vaze & Helfrich-Förster, 2016) and D. montana (Kauranan et al, 2019;Tyukmaeva et al, 2020).…”