The role of inbreeding depression and mating system in the evolution of heterostyly

We investigated the role of morph-based differences in the expression of inbreeding depression in loss of the mid-styled morph from populations of tristylous Oxalis alpina as proposed by theoretical analyses. The extent of self-compatibility of reproductive morphs, the degree of self-fertilization, and the magnitude of inbreeding depression were investigated in three populations of O. alpina differing in their tristylous incompatibility relationships. All three populations exhibited significant inbreeding depression. In two populations with highly modified tristylous incompatibility, manifested as increased reciprocal compatibility between short- and long-styled morphs, substantial self-compatibility and self-fertilization of mid-styled morphs was detected, and expected to result in expression of inbreeding depression in the progeny of mid-styled morphs in the natural populations. In contrast, significant self-fertility of the mid-styled morph was absent from the population with typical...