Inbreeding depression and mating systems in two species of Linanthus (Polemoniaceae)

Theory predicts that, at equilibrium, the magnitude of inbreeding depression caused by recessive alleles should decrease as the level of self-fertilization increases, facilitating the evolution of even higher selfing rates. Data are presented on mating systems and inbreeding depression in multiple populations of two annual species in the genus Linanthus (Polemoniaceae). Outcrossing rates were found to be less than 0.075 in populations of a small-flowered species, L. bicolor, and ranged from 0.104 to 0.300 in populations of a larger-flowered species, L. jepsonii. Inbreeding depression for both species was low for all life history stages, with cumulative inbreeding depression less than 0.23 in all populations. Significant inbreeding depression for pollen fertility was found in L. jepsonii populations and may contribute substantially to total inbreeding depression. A competitive treatment had no significant effect on the expression of inbreeding depression for above-ground dry mass. In accordance with theoretical expectations, the magnitude of inbreeding depression was lower in L. bicolor, the more highly selfing species. The magnitude of inbreeding depression in L. jepsonii, although greater than that of L. bicolor, is not sufficient to prevent evolution of increased selfing rates in this species, according to some theoretical models of mating system evolution.