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Thesis (M.S.)—University of Nebraska—Lincoln, 1950. Department of Zoology.


Copyright 1950, the author. Used by permission.


This study attempted to show effects of competition in developmental stages on D. affinis and D. pseudoobscura when cultured together.One strain of affinis (Clarinda, Iowa) and two of pseudoobscura (Lincoln, Nebraska) were used.Eggs were counted into culture bottles, either all the eggs being of the same strain or half being from the affinis strain and half from one of the pseudoobscura strains.With respect to numbers of eggs, two series were run, using 300 and 600 eggs per culture bottle respectively.The temperature ranges were employed, with averages approximately 200 and 250 C. All combinations of these conditions (regarding kinds of eggs, degree of crowding, and temperature) were used.

The results were quite heterogeneous, probably partly because of the genetic variability of the stocks used.

There was no indication that either species had an effect on the other under the conditions of observation.It seemed to make little difference whether the flies were cultured one or two species per bottle.

There were no appreciable differences between the two strains of pseudoobscura.

Crowding had little effect on the adult hatch frequency but tended to reduce the rate of development in all three strains.

The species were observed to be different in the following way:

  1. Affinis had a more nearly constant hatch frequency under all the various conditions of the experiment than did pseudoobscura.

  2. Affinis seemed to have a larger proportion of females than did pseudoobscura, although, for all the strains, frequencies of females were generally in excess of frequencies of males; and

  3. The mean rate of development of affinis was regularly greater than that of pseudoobscura under corresponding conditions.

It is pointed out that, because of the likelihood of considerable natural variation in the genetic factors responsible for these characters, the observed differences between affinis and pseudoobscura may not be considered to be necessarily general for these species.

Advisor: Dwight D. Miller