. The Biological bulletin. Biology; Zoology; Marine biology. 182 R. G. STROSS AND J. C. HILL Critical photoperiod The switch to sexual reproduction was transitional at hours of light at 19° C. (Fig. 3). One-half of the reproduction was in the form of sexual broods at L:D 12f:llJ. Temperature influenced the critical photoperiod only slightly. At 12° one-half of the broods were sexual at 13:11, a shift of 15 minutes, with a temperature change of seven degrees. Sexual reproduction was maximally intense at L:D 12:12. The response was not so intense in cultures of the Peter Lake stock when tes
. The Biological bulletin. Biology; Zoology; Marine biology. 182 R. G. STROSS AND J. C. HILL Critical photoperiod The switch to sexual reproduction was transitional at hours of light at 19° C. (Fig. 3). One-half of the reproduction was in the form of sexual broods at L:D 12f:llJ. Temperature influenced the critical photoperiod only slightly. At 12° one-half of the broods were sexual at 13:11, a shift of 15 minutes, with a temperature change of seven degrees. Sexual reproduction was maximally intense at L:D 12:12. The response was not so intense in cultures of the Peter Lake stock when tested at the standard density of 5 individuals/20 ml. Nevertheless, the capacity 1-. HOURS OF LIGHT PER DAY Figure 3. Photoperiod and sexual reproduction in cultures of D. pulex (Paul Lake strain) started with young born at the indicated photoperiod. A standard density of 5 individ- uals was maintained in each replicate throughout the experiment (30 days). Figures 3 and 4 reproduced by permission of Science, volume 150, p. 1462, 1965. Copy- right 1965 by the American Association for the Advancement of Science. of cultures from Peter Lake to produce ephippia under short-day photoperiods is demonstrated. In short days (L:D 12:12) at 19° C, of the broods were ephippial. No sexual broods were produced at L:D 16:8. At 12° the cultures produced a maximum of 32% sexual broods at L:D 12:12 and 13:11 and none at longer photoperiods. The response of Paul Lake cultures under identical condi- tions was to produce all sexual broods at L:D 12:12 and 50% sexual broods at 13:11. That photoperiodic control is involved was shown by the use of so-called skeleton photoperiods in testing Peter Lake stock. Asymmetric skeletons, con-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lilli
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