Figure 1.
Geographic and climatic origin and phylogeny of analyzed Drosophila species.
(A) Ancestral ranges are shown for each species [17], [47],[48]. While D. melanogaster and D. simulans are now cosmopolitan and D. ananassae is expanding in the tropics (green), their presumed ancestral ranges are shown. D. virilis is holarctic (gray) and restricted from the tropics, with a poor understanding of its ancestral range. Other species are more or less found in their native ranges, covering a variety of climates. Sites of collection are noted by arrows. (B) The phylogeny of the sequenced Drosophila species. Many of the tropical species are closely related, though D. willistoni serves as a tropical out-group compared to the melanogaster and obscura groups. Branch lengths are based on evolutionary divergence times [49]. (C) Range sizes vary considerably between the species.
Table 1.
Drosophila species and strains.
Figure 2.
Developmental landmarks used in study.
Many images of each stage (examples on the left) were averaged to generate composite images (lateral view on the right) for each of the developmental stages, of which 29 are shown.
Table 2.
Major morphological events in Drosophila development.
Table 3.
Drosophila development videos.
Figure 3.
Developmental time of D. melanogaster varies with temperature.
(A) Images of developing D. melanogaster embryos at each temperature are shown for a selection of stages to highlight the overall similarity of development. (B) The time individual animals reached the various time-points are shown, with each event being a different color. Time 0 is defined as the end of cellularization, when the membrane invagination reaches the yolk. Between 17.5°C and 27.5°C the total time of embryogenesis, measured as the mean time between cellularization and trachea fill, has a logarithmic relationship to temperature described by
where T is temperature in °C (
). (C) The developmental rate in D. melanogaster changes uniformly with temperature, not preferentially affecting any stage. Timing here is normalized between the end of cellularization and the filling of the trachea.
Figure 4.
Drosophila species develop at different rates and respond to temperature in distinct ways.
(A) Images of developing embryos of each species are shown to scale. All species go through the same stages in the same order at all viable temperatures. (B) At 17.5°C all species show uniformly long developmental times, with D. virilis and D. mojavensis being significantly longer than other species. (C) At 22.5°C and (D) 27.5°C there is considerably more variation between species. While developmental times decrease with increasing temperature across all species, the effect is muted in the alpine species. (E) At 30°C, developmental rate has stopped accelerating and the alpine species are seeing considerable slow-down in development time.
Figure 5.
Temperature dependent developmental rates are climate specific.
The time between the end of cellularization and trachea fill are shown for all species at a range of temperatures. The climatic groups – tropical (warm colors), alpine (blues), temperate (purple), and sub-tropical (green) – clearly stand out from one another to form four general trends.
Figure 6.
Proportionality of developmental stages is not affected by non-heat-stress temperatures.
(A) Across species, development maintains the same proportionality. D. pseudoobscura stands out as not being co-linear at higher temperatures. Instead, the later part of its development is slowed and takes up a disproportionally long time. (B) Plotting proportionality across all species and all temperatures reveals the approximately normally distributed proportionality of all morphological stages.
Table 4.
The timing of specific developmental events can be predicted as a function of total developmental time.
Table 5.
The developmental time of embryos between 17.5°C and 27.5°C is a species-specific function of temperature.