NEGATIVE CORRELATION BETWEEN MALE ALLOCATION AND RATE OF SELF-FERTILIZATION IN A HERMAPHRODITIC ANIMAL

Sex-allocation theory predicts that the evolution of increased rates o f self-fertilization should be accompanied by decreased allocation to male reproduction (sperm production and broadcast). This prediction ha s found support in plants but has not previously been tested in animal s, which, in contrast to biotically pollinated plants, are free of com plications associated with incorporating the costs of attractive struc tures such as petals. Here we report rates of self-fertilization as we ll as proportional allocation to male reproductive tissues within popu lations of the simultaneous hermaphrodite Utterbackia imbecillis, a fr eshwater mussel. Individuals from populations with higher selfing rate s devoted a lower proportion of reproductive tissue to sperm productio n (correlation = -0.99), in support of theory.