Color inheritance in Fundulus hybrids

Abstract

In the hybrids of Fundulus heteroclitus and Fundulus majalis it was found that, in general, wherever the color characters were not concerned with the rate of development, the F. heteroclitus characters were dominant over those of F. majalis. These dominant characters were:

1. Red yolk chromatophores large and abundant.

2. Black yolk chromatophores large and usually polygonal in shape.

3. An early first crop of head chromatophores is present, in addition to a later crop which is found in both pure species and both hybrids.

4. There is a row of red chromatophores on the lateral line shortly before and immediately after hatching. As soon as the fish hatch the red chromatophores begin to fade, and within a few days disappear entirely.

On the other hand, when the characters were concerned with the rate of development, the Mendelian dominance was partly or entirely obscured. These characters were:

5. In F. heteroclitus there are no or very few black chromatophores on the lateral line at hatching; but they increase rapidly during the first few days after hatching. In F. majalis there are 50 or 60 black lateral line chromatophores at hatching. The hybrids are intermediate.

6. In F. heteroclitus when the yolk chromatophores first appear they are uniformly distributed over the whole yolk; while in F. majalis they are confined to the hemisphere containing the embryo. The hybrids are intermediate.

7. Both with respect to time, and with respect to the stage of development of the embryo the yolk chromatophores appear first in F. heteroclitus, next in the F. heteroclitus egg hybrid, next in the F. majalis egg hybrid, and last in the pure F. majalis.

An apparent case of blended inheritance in the time of the first appearance of head pigment was found to be really a case of the combination of two crops of head chromatophores, one of which did not develop in the recessive species F. majalis.