ADAPTATIONS TO TEMPERATE CLIMATES AND EVOLUTION OF OVERWINTERING STRATEGIES IN THE DROSOPHILA MELANOGASTER SPECIES GROUP

Abstract

The Drosophila melanogaster species group is considered to have originated in the tropics and only recently invaded temperate habitats. The temperate species of this group that were studied here may be subdivided into the warm-temperate species (D. lutescens and D. rufa) and the cool-temperate species (species of the auraria complex). The warm-temperate species were more cold-hardy than were their tropical relatives (D. takahashii or D. melanogaster) at the larval and imaginal stages, and the cool-temperate species were more cold-hardy than the warm-temperate species, although only at the imaginal stage. However, these species showed little or no intraspecific variation in cold-hardiness, in spite of great variation in winter temperature within the species' ranges. It is assumed that cold-hardiness is one of the main factors restricting their distributions at high latitudes and that it is the key for evolution of the warm- and cool-temperate species from their subtropical or warm-temperate ancestors. Both warm- and cool-temperate species had photoperiodically controlled reproductive diapause. In the cool-temperate species, the development of cold-hardiness was affected by diapause, but diapause had little or no effect on cold-hardiness in the warm-temperate species. Critical daylengths and the diapause rates varied from species to species according to variation in their overwintering plans and also varied geographically in consequence of their adaptation to local climates. Species showed different responses to temperature in preimaginal and ovarian development. These differences are considered to reflect adaptation to different environmental temperatures.

Cold and heat tolerance of drosophilid flies with reference to their latitudinal distributions

“…In addition, no difference was observed in cold tolerance between the Sapporo and Tokyo strains of D. auraria and D. suzukii. Also in other drosophilid species including the present experimental species (D. takahashii, D. lutescens and D. rufa), geographic variation in cold tolerance has been reported to be negligible or small (Kimura 1982(Kimura , 1988(Kimura , 2001Kimura et al 1994;Coyne et al 1983;Hoffmann and Parsons 1991;Hoffmann et al 2003;David et al 2003). Thus, evolutionary capacity of a drosophilid species to increase cold tolerance seems to be limited.…”

“…temperature that immobilizes animals) which is assumed to be an ecologically more relevant measure of temperature adaptation (Berrigan and Hoffmann 1998). Moreover, the adult stage is more tolerant to cold than any other developmental stages in drosophilid species except for those that overwinter at the larval or pupal stage (Tucic 1979;Kimura 1988;Kimura and Beppu 1993;Kimura et al 1994). Furthermore, the effect of the diapause state on LT 50 is not so large (Ohtsu et al 1998(Ohtsu et al , 1999Hori and Kimura 1998;Goto et al 1998Goto et al , 1999.…”

“…This may raise a question as to the appropriateness of the present results in assessment of overwintering ability of experimental species or strains. For example, cold-tolerance changes by acclimation (Kimura 1988;Hoffmann et al 2003), and therefore it may be more appropriate to compare their overwintering ability with maximum tolerance. However, the ability of acclimation has been reported to be rather constant among drosophilid species (Ohtsu et al 1998(Ohtsu et al , 1999Hori and Kimura 1998;Goto et al 1998Goto et al , 1999, indicating that species showing higher cold-tolerance in the present experiments are also higher in maximum tolerance.…”

“…If they have such capacities, they would become more coldhardy and expand beyond the boundary. In a number of insects including several species of Drosophila, no or a very low level of geographic variation has been observed in cold tolerance (Danilevskii 1965;Eger et al 1982;Coyne et al 1983;Kimura 1988Kimura , 2001Kimura et al 1994), suggesting that they have limited capacities to increase their cold tolerance. However, a number of studies (reviewed by Hoffmann et al 2003;David et al 2003) observed in some other species of Drosophila that cold tolerance increases with the latitude of source population.…”

Rhythmic components of photoperiodic time measurement in the pitcher-plant mosquito, Wyeomyia smithii

“…In temperate Japan, the incidence of diapause in D. auraria at a fixed temperature and photoperiod, as well as the critical photoperiod (CPP), increases with latitude (Kimura 1984(Kimura , 1988Pittendrigh and Takamura 1987). The similarity between the latitudinal cline of the eclosion pacemaker of D. auraria Takamura 1987, 1989) and the latitudinal cline in the amplitude and temperature dependency of the PPRC of adult diapause lead Pittendrigh et al (1991) to propose an ''amplitude hypothesis'' for PTM.…”