TEMPERATURE AND THE RATE OF EMBRYONIC DEVELOPMENT
By C.B. Kimmel and B. Ullmann, Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403-1254, USA.
We have used the staging series (The Zebrafish Book, Edition 2.1, p. 3.27, 1994) to learn how zebrafish development varies as a function of incubation temperature. This information is useful because different studies do not all use the same temperature, and moreover, one might use temperature as a tool to change developmental rate, e.g. to bring embryos from one batch to two different stages at once for heterochronic transplantation.
We found that between 25°C and 33°C the relationship between development and temperature is approximately linear. In the accompanying figure, we show selected developmental stages along the ordinate and incubation time along the abscissa. Note that the time scale is expanded in A relative to B, but that the slopes of the lines are the same in both panels. (Data points represent averages from groups of embryos, as we plan to describe in more detail elsewhere.) Each figure is scaled so that the diagonal line (i.e. a line with a slope of 45°) corresponds to the rate of development at 28.5°C, the standard temperature described in the staging series. We reconfirmed the developmental rate at this temperature for a set of control embryos developing at 28.5°C (not shown).
Because of the apparent linearity, a simple calculation allows one to determine approximately when embryos developing at any temperature between 25°C and 33°C will reach a desired state of interest:
HT = h/(0.055T- 0.57)
where HT = hours of development at temperature T, and h = hours of development to reach the stage at 28.5°C, as set out below, and in more detail in Table 2 from the staging series.
We have not systematically investigated developmental rate outside of this temperature range. We selected these extremes because unpublished experiments from the Streisinger lab suggested they were near the limits at which development can proceed normally. In fact, 33°C appears to be at the upper limit (not shown), but development may be normal somewhat below 25°C (see Shiorone and Gross, 1968, J. Exp. Zool. 169, 43-52).
We did not find any differences in when or how various features of the embryo develop, relative to one another, at different temperatures. However, one should perhaps be cautious about making direct comparisons between embryos reared at different temperatures: there is no assurance that rates of development of more cryptic features, such as when a marker gene is expressed or when a cell becomes committed to this or that fate, are all coordinately regulated.
Stage abbreviations in the figure (including time to reach the stage at 28.5°C): 8c: 8-cell (1.25h), 64c: 64 cell (2 h), 1kc: 1,000-cell (3 h), d: dome (4.3 h), s: shield (6 h), 75%: 75%-epiboly (8 h), b: bud (10 h), 1s: 1 somite (10.3 h), 14s: 14-somite (16 h), 20s: 20 somite (19 h), p5: prim-5 (24 h), p15: prim-15 (30 h), p24: prim-24 (36 h), hb: high bud (42 h), lb: long bud (48 h), pf: pec fin (60 h), pm: protruding mouth (72 h). See also, The Zebrafish Book.
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