Figure 1.

Experimental crossing design. Adult urchins were conditioned for four months to either non-upwelling conditions (N) or upwelling conditions (U). Gametes from two males and two females from each condition were crossed reciprocally, generating four distinct crosses, each replicated four times. Two replicates from each cross were reared in the same condition as the parents (NN, UU) or the opposite condition (NU, UN). Two by two crosses for each parental condition were performed five times in succession for a total of 40 unique crosses. Spicule length and body length were measured in prism stage larvae, pictured. (Online version in colour.)