Adaptation to a seasonally varying environment: a strong latitudinal cline in reproductive diapause combined with high gene flow in Drosophila montana

Abstract

Adaptation to seasonal changes in the northern hemisphere includes an ability to predict the forthcoming cold season from gradual changes in environmental cues early enough to prepare for the harsh winter conditions. The magnitude and speed of changes in these cues vary between the latitudes, which induces strong selection pressures for local adaptation.We studied adaptation to seasonal changes in Drosophila montana, a northern maltfly, by defining the photoperiodic conditions leading to adult reproductive diapause along a latitudinal cline in Finland and by measuring genetic differentiation and the amount of gene flow between the sampling sites with microsatellites. Our data revealed a clear correlation between the latitude and the critical day length (CDL), in which half of the females of different cline populations enter photoperiodic reproductive diapause. There was no sign of limited gene flow between the cline populations, even though these populations showed isolation by distance. Our results show that local adaptation may occur even in the presence of high gene flow, when selection for locally adaptive life-history traits is strong. A wide range of variation in the CDLs of the fly strains within and between the cline populations may be partly due to gene flow and partly due to the opposing selection pressures for fly reproduction and overwinter survival. This variation in the timing of diapause will enhance populations’ survival over the years that differ in the severity of the winter and in the length of the warm period and may also help them respond to long-term changes in environmental conditions.

Latitudinal clines: an evolutionary view on biological rhythms,

“…Positive correlations between CPP and latitude were later described in many other diapausing insects (figure 3a; reviewed by Tauber et al [8] and Danks [12]). Latitudinal clines in CPP have further been demonstrated in adult reproductive diapause in the Japanese flower bug Orius [19] and in Finnish malt flies Drosophila montana [21], in pupal diapause in the butterfly Sericinus montelus [13] and in maternally induced larval diapause in the parasitoid wasp Nasonia vitripennis [20]. The combined data reveal a general positive correlation between CPP and latitude, with an increased slope above approximately 408 N ( figure 3a).…”

Diapause termination of Rhagoletis cerasi pupae is regulated by local adaptation and phenotypic plasticity: escape in time through bet‐hedging strategies

“…Adults from K. Nera are known to emerge earlier than those from Dafni in local field conditions, and reciprocal transplant experiments (between these two populations in field) revealed a genetic basis to geographical variation of diapause intensity (Papanastasiou et al ., ), implying that the above populations are not ecologically exchangeable, despite the presence of gene flow (Rader et al ., ). Thus, the existence of local adaptation in the timing of diapause termination of R. cerasi pupae, even under conditions of ongoing gene flow, is in agreement with recent related studies regarding to the yellow dung fly and Drosophila montana (Demont et al ., ; Tyukmaeva et al ., ). Nevertheless, conditions experienced mostly by egg and larvae in the field before being brought back to the laboratory for collecting pupae remain uncontrolled (the initial rearing environment cannot be controlled in R. cerasi s because of lack of efficient rearing methodology; Köppler et al ., ) and might add some variability in diapause responses.…”

Myo-inositol as a main metabolite in overwintering flies: seasonal metabolomic profiles and cold stress tolerance in a northern drosophilid fly

“…At least in the Kemi population, which is approximately 100km south of Oulanka, the few females that emerge during early July are known to develop their ovaries (Aspi et al, 1993). The second set of flies was transferred into the experimental conditions at a photoperiod of 16h:8h light:dark, corresponding to August, when the emerging females of the wild population enter diapause in northern Finland (Aspi et al, 1993;Tyukmaeva et al, 2011). In addition to the flies from the mass-bred population, we used two sets of males from three isofemale strains (see above).…”