Figure 1.—

Experimental design. See text for details of experimental procedure. Open circles indicate yellow snails and solid circles indicate brown snails. Comparison between half-sib broods of the common mother with different fathers was made by comparing SR1 and SR3 or SR2 and SR4. For the common father with different mothers, SR1 and SR4 or SR2 and SR3 were compared. Comparison was made between full-sib broods SR1 and SR5 or SR2 and SR6.