Evolution__3rd_Edition

(a) (b)
Plate 7
Prezygotic isolation by color differences in two cichlids. (a) In normal light, the two species differ in coloration. Pundamilia nyererei
(above) has red colors and P. pundamilia has blue (look at the tail fins, for instance). The red females mate only with red males, and
blue females only with blue males. (b) In an experiment with monochromatic orange light, the two species were indistinguishable.
Now the red females mated indiscriminately with red and blue males, as did the blue females. The offspring were all viable and fertile.
The experiment shows that the two species are held apart by the color-based mating preferences. It also suggests that the species have
evolved very recently because there is no postzygotic isolation (Section 13.3.3, p. 358). (Photos courtesy of Ole Seehausen.)