Selection for reproduction under short photoperiods changes diapause-associated traits and induces widespread genomic divergence.

The incidence of reproductive diapause is a critical aspect of life history in overwintering insects from temperate regions. Much has been learned about the timing, physiology and genetics of diapause in a range of insects, but how the multiple changes involved in this and other photoperiodically regulated traits are inter-related is not well understood. We performed quasinatural selection on reproduction under short photoperiods in a northern fly species, , to trace the effects of photoperiodic selection on traits regulated by the photoperiodic timer and/or by a circadian clock system.

Direct and correlated responses to bi-directional selection on pre-adult development time in Drosophila montana.

Selection experiments offer an efficient way to study the evolvability of traits that play an important role in insects' reproduction and/or survival and to trace correlations and trade-offs between them. We have exercised bi-directional selection on Drosophila montana flies' pre-adult development time under constant light and temperature conditions for 10 generations and traced the indirect effects of this selection on females' diapause induction under different day lengths, as well as on the body weight and cold tolerance of both sexes. Overall, selection was successful towards slow, but not towards fast development.

Strength of sexual and postmating prezygotic barriers varies between sympatric populations with different histories and species abundances.

The impact of different reproductive barriers on species or population isolation may vary in different stages of speciation depending on evolutionary forces acting within species and through species' interactions. Genetic incompatibilities between interacting species are expected to reinforce prezygotic barriers in sympatric populations and lead to cascade reinforcement between conspecific populations living within and outside the areas of sympatry. We tested these predictions and studied whether and how the strength and target of reinforcement between Drosophila montana and Drosophila flavomontana vary between sympatric populations with different histories and species abundances.

Diapause affects cuticular hydrocarbon composition and mating behavior of both sexes in Drosophila montana.

Environmental cues, mainly photoperiod and temperature, are known to control female adult reproductive diapause in several insect species. Diapause enhances female survival during adverse conditions and postpones progeny production to the favorable season. Male diapause (a reversible inability to inseminate receptive females) has been studied much less than female diapause.

Circadian clock of Drosophila montana is adapted to high variation in summer day lengths and temperatures prevailing at high latitudes.

Photoperiodic regulation of the circadian rhythms in insect locomotor activity has been studied in several species, but seasonal entrainment of these rhythms is still poorly understood. We have traced the entrainment of activity rhythm of northern Drosophila montana flies in a climate chamber mimicking the photoperiods and day and night temperatures that the flies encounter in northern Finland during the summer. The experiment was started by transferring freshly emerged females into the chamber in early and late summer conditions to obtain both non-diapausing and diapausing females for the studies.