Experiments with Drosophila Ampelophila concerning Evolution

Experiments with Drosophila Ampelophila concerning Evolution

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Experiments with Drosophila Ampelophila concerning Evolution

Experiments with Drosophila Ampelophila concerning Evolution

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Practically all the experimental studies of inheritance have extended through but few, rarely more than 6, generations and have been concerned with pairs of non-intergrading characters. In the present work more than 70 generations have been reared. This was possible for two reasons: Drosophila ampelophila Loew has a very short life-history, and it can be kept breeding throughout the year. The character abnormal wing-venation, the inheritance of which was studied, may be made to exhibit extreme variability, passing from less venation than normal through normal to extra venation, so great that the additional veins almost equal the normal in extent.

At the Boston (1907) meeting of the International Zoölogical Congress a preliminary report was presented upon this subject, 6 generations having been obtained. During the summer of 1908 a report upon the work (covering about 25 generations) done at the Station for Experimental Evolution was submitted to the Director, but I deferred publication because I wished to test more in detail certain points, especially sexual selection and the further fate of the abnormal strains. This additional work was done at the American Museum of Natural History. Incidentally I obtained confirmation of the previous work, but for the most part the present paper includes only the Cold Spring Harbor data and the conclusions drawn are as given in the 1908 report, except where otherwise indicated.

MATERIAL AND METHODS.

Drosophila ampelophila (the small red-eyed "pomace-fly") is very common about cider-mills, ripe fruit, vinegar-barrels, and the like. The larvæ normally live in the pulp of rotting fruits, especially during the acetic-acid stage of decay. They will, however, thrive on the side of a tumbler containing fruit-juices, and I have reared them through several generations on stale beer. At a temperature of 25° C. the eggs hatch in 40 hours or less. The duration of the larval period is, on the average, 5 days, and of the pupal period 4⅔ days. The adults become sexually mature about 48 hours after emergence when kept at this temperature. They live for about 3 weeks. The mean number of eggs is close to 200. Copulation is repeated and frequent.

Most of the flies discussed in this paper were bred in an incubator, where an average temperature of 25.5° C. was maintained. A thermographic record was kept. Since the temperature of the incubator was so nearly that of the working-room, absolute constancy was not obtained. The amount of variation is shown in fig. 1, which gives the frequencies . . .

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