Effects of cross and self-fertilization on progeny fitness in Lobelia cardinalis and L. siphilitica

Abstract

Measured inbreeding depression in both survival and fertility in two sympatric, short-lived, perennial herbs: hummingbird-pollinated Lobelia cardinalis (two populations) and bumblebee-pollinated L. siphilitica (one population). In all three populations, selfing had nonsignificant effects on the number and size of seeds. Lobelia siphilitica and one population of L. cardinalis exhibited significant levels of inbreeding depression between seed maturation and germination, excluding the consideration of possible differences in dormancy or longterm viability in the soil. There was no inbreeding depression in subsequent survival in any population. In the field, significant survival differences between selfed and outcrossed progeny occurred only in two years and in only one population of L. cardinalis. For both survival and fertility there was little evidence for the expected differences among families in inbreeding depression. Compared to survival, inbreeding depression in fertility (flower number) tended to be much higher. By first-year flower production, the combined effects on survival and flower number caused inbreeding depression in net fertility to reach 54%, 34% and 71% for L. siphilitica and the two populations of L. cardinalis. By the end of the second year of flowering in the field, inbreeding depression net fertility was 53% for L. siphilitica and 54% for one population of L. cardinalis. For the other population of L. cardinalis, these values were 76% through the second year of flowering and 83% through the third year. Such high levels of inbreeding depression should strongly influence selection on those characters affecting self-fertilization rates in these two species. -from Author