The early effects of conjugation on the division rate of Spathidium spathula

Abstract

Conjugation occurred readily in a pedigree culture of Spathidium spathula and therefore experiments were started to determine the effects of fertilization in the life history of the organism. During the first six months of the work, more than sixty lines were derived directly or indirectly from the parent line by conjugation. Some of the exconjugant lines studied represent the F₁, F₂, F₃, and F₄ generations. All the lines which are compared were bred under identical cultural conditions.

A comparison of the number of generations attained by each exconjugant line with that attained by its parent line during the first 15 days after the former's origin gives the following results. Forty-two exconjugant lines produced more generations, eight produced less generations and two produced essentially the same number of generations as their respective parent lines. The various cases in which the parent line did not survive the first fifteen days after the exconjugant line was derived from it are not comprised in these data. If such cases were included it obviously would increase the number of plus cases of exconjugant lines.

Analysis of the data thus far obtained inevitably leads to the conclusion that the exconjugant lines of this pedigree culture of Sputhidium, under the conditions of the experiment, exhibit, in the great majority of cases, a higher division rate for the first fifteen days after conjugation than the parent lines.

The evidence to date also indicates that exconjugant lines which are derived from old parent lines (i.e. from lines which have undergone many generations since conjugation) show a relatively greater increase in the division rate, during the first fifteen days, as compared with the parent lines, than do exconjugant lines which are derived from young parent lines (i.e., from lines which have more recently conjugated).