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Abstract
Winter ecology of natural enemies has a great influence on the level and efficiency of biological control at spring. The hoverfly Episyrphus balteatus (DeGeer) (Diptera: Syrphidae) is one of the most important natural predators of crop aphids in Europe. Three different overwintering strategies coexist in this species which makes it a good model in order to study ecologically-based speciation processes. The purpose of this study was to determine whether E. balteatus populations with alternative overwintering strategies are genetically differentiated. To that aim, we developed 12 specific microsatellite markers and evaluated the level of neutral genetic differentiation between E. balteatus field populations that overwinter in the three different ways described in this species (i.e. migration, local overwintering at a pre-imaginal stage, and local overwintering at adult stage). Results showed a lack of neutral genetic differentiation between individuals with different overwintering strategies although there are strong ecological differences between them. All pair-wise FST values are below 0.025 and non-significant, and Bayesian clustering showed K = 1 was the most likely number of genetic clusters throughout our sample. The three overwintering strategies form one unique panmictic population. This suggests that all the individuals may have genetic material for the expression of different overwintering phenotypes, and that their commitment in one particular overwintering strategy may depend on environmental and individual factors. Consequently, the prevalence of the different overwintering strategies would be potentially modified by landscape engineering and habitat management which could have major implications for biological control.
Highlights
Insect body temperature varies in relation with the environmental temperature
Ecological differences between E. balteatus individuals overwintering with different strategies led us to hypothesize reproductive isolation among them
According to the classification proposed by Rundle and Nosil [31], E. balteatus winter ecology is likely to produce three forms of reproductive isolation involved in ecological speciation: habitat isolation, temporal isolation and natural selection against immigrants
Summary
Insect body temperature varies in relation with the environmental temperature. This results in insect life cycles being highly dependent on climatic conditions. In temperate regions, adaptation to winter conditions is an important life history trait that may influence the ecological and evolutionary success of insects. To cope with adverse winter conditions, insects have developed a great variety of ecological strategies including migration [1,2] and diapause [3] that can occur simultaneously in the same species [4]. Alternative overwintering strategies may lead to allopatry or allochrony in reproduction between individuals adopting distinct strategies, resulting in a reduction of genetic mixing. Migration is notably known in birds to be involved in genetic divergence between sedentary and migratory populations, or between populations displaying different migration patterns [5,6]
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