Fig. 3.

Parallel speciation between marine and stream-resident strickleback. (A) Photo showing typical specimens from the marine (Upper) and stream-resident populations (Lower). The forms differ in defensive body armor and body size (both greater in the marine form), along with many other morphological traits. (Photo by J. McKinnon.) (B) Mating compatibility between males and females taken from different marine and stream stickleback populations around the Northern Hemisphere. Compatibility is measured by the proportion of mating trials reaching the penultimate stage of the courtship sequence. Fish were sampled from multiple populations in both the Atlantic and Pacific ocean basins. [Reproduced with permission from ref. 52 (Copyright 2004, Nature Publishing Group).]