Abstract
Seasonal polyphenism in Drosophila suzukii manifests itself in two discrete adult morphotypes, the “winter morph” (WM) and the “summer morph” (SM). These morphotypes are known to differ in thermal stress tolerance, and they co‐occur during parts of the year. In this study, we aimed to estimate morph‐specific survival and fecundity in laboratory settings simulating field conditions. We specifically analyzed how WM and SM D. suzukii differed in mortality and reproduction during and after a period of cold exposure resembling winter and spring conditions in temperate climates. The median lifespan of D. suzukii varied around 5 months for the WM flies and around 7 months for the SM flies. WM flies showed higher survival during the cold‐exposure period compared with SM flies, and especially SM males suffered high mortality under these conditions. In contrast, SM flies had lower mortality rates than WM flies under spring‐like conditions. Intriguingly, reproductive status (virgin or mated) did not impact the fly survival, either during the cold exposure or during spring‐like conditions. Even though the reproductive potential of WM flies was greatly reduced compared with SM flies, both WM and SM females that had mated before the cold exposure were able to continuously produce viable offspring for 5 months under spring‐like conditions. Finally, the fertility of the overwintered WM males was almost zero, while the surviving SM males did not suffer reduced fertility. Combined with other studies on D. suzukii monitoring and overwintering behavior, these results suggest that overwintered flies of both morphotypes could live long enough to infest the first commercial crops of the season. The high mortality of SM males and the low fertility of WM males after prolonged cold exposure also highlight the necessity for females to store sperm over winter to be able to start reproducing early in the following spring.
Highlights
Phenotypic plasticity can be defined as the ability of a given genotype to produce different phenotypes in response to environmental stimuli (Davidson, Jennions, & Nicotra, 2011; Gibert, Peronnet, & Schlötterer, 2007)
summer morphotype (SM) males had the highest mortality compared to the other groups of flies, with 7% of them dying during the 8-day pre-cold acclimation, and another 9% dying during the 31-day cold exposure at 5°C (Figure 2b)
We analyzed how D. suzukii seasonal morphotypes differed in mortality and reproduction during and after a prolonged period of cold exposure resembling winter and spring conditions in temperate climates
Summary
Phenotypic plasticity can be defined as the ability of a given genotype to produce different phenotypes in response to environmental stimuli (Davidson, Jennions, & Nicotra, 2011; Gibert, Peronnet, & Schlötterer, 2007). The striking phenotypic differences between SM and WM of D. suzukii affect their individual performances under prevailing conditions, they may have an impact on their seasonal population dynamics Individuals of both seasonal morphotypes co-occur in autumn and in spring (Leach, Stone, Van Timmeren, & Isaacs, 2019; Panel et al, 2018; Shearer et al, 2016), but they are expected to have different life-history strategies, in particular regarding the investment in reproduction and survival. Our goal was to better understand the population dynamics of D. suzukii in early spring, a crucial period for population build-up and initial host infestation
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