Breeding System Evolution in Leavenworthia: Breeding System Variation and Reproductive Success in Natural Populations of Leavenworthia Crassa (Cruciferae)

Abstract

Populations of Leavenworthia crassa (Cruciferae) studied for 3 years exhibited among‐ and within‐population genetic variation for a suite of floral and reproductive traits (flower width, petal length, anther position, ability to set seeds in the absence of pollinators, time to first flowering) associated with breeding system. We used electrophoretic markers to show that a population with small, monomorphically colored flowers with introrse anthers had a significantly lower outcrossing rate (t = 0.03) than did a population with larger, polymorphically colored flowers with extrorse anthers (t = 0.33). In the more‐outcrossing population the correlation between higher maternal plant outcrossing rate and the suite of six traits approached significance (P < 0.067), with greater petal size, greater flower width, and reduced ability to set seeds in the absence of pollinators contributing significantly. Plants in selfing populations had a generally higher reproductive success, with a higher number of flowers per plant, a smaller proportion of unfertilized ovules, a smaller proportion of fertilized ovules aborted, a higher rate of fruit set, and overall a larger number of seeds matured than did plants from the more outcrossing populations. Pollen limitation did not appear to account for lower reproductive success in outcrossing populations. Resource limitation did not differ substantially between populations. However, within‐ovary patterns of fertilization, abortion, and seed weight were significantly less random in outcrossing populations than in selfing populations, suggesting that differential gamete and embryo success may be responsible for lower reproductive success in outcrossing populations.

Phylogenetic Relationship between Degree of Self-compatibility and Floral Traits in Lilium longiflorum Thunb. (Liliaceae)

“…Quantitative variation of SI among individuals has often been observed within species (Kokubun et al, 2006;Levin, 1996;Lloyd, 1968;Reinartz and Les, 1994;Stebbins, 1957;Stephenson et al, 2003), and the geographic distribution of individuals categorized by SI strength was also confirmed (Goodwillie and Ness, 2005;Inoue, 1988;Kokubun et al, 2006;Lipow et al, 1999;Lloyd, 1968;Lyons and Antonovics, 1991;Ortiz et al, 2006;Stone et al, 2006;Tsukamoto et al, 1999). These previous studies, however, covered only a few populations (but see Kokubun et al, 2006;Lloyd, 1968) and estimated SI/SC as a qualitative trait, but not a quantitative trait.…”

“…The change of these floral traits is often accompanied by mating system evolution from outcrossing to selfing. Increase in the selfing rate is often associated with smaller flowers (Goodwillie and Ness, 2005;Lyons and Antonovics, 1991;Wyatt, 1984), resulting from the decrease of investing cost in sexual organs. Autonomous selfing in some self-compatible populations in the Ryukyu Archipelago is suggested by a significant excess of homozygous genotypes in the same allozyme loci and relatively high fixation indices of the population (Hiramatsu et al, 2001a) and, in fact, a high selfing rate and lack of outcrossing were observed in the field in self-compatible populations on Yakushima Island and Kikaijima Island in the Ryukyu Archipelago (M. Hiramatsu, unpublished data).…”

“…Loss of selfincompatible individuals from a population is often associated with changes to the mating system, particularly selection favoring selfing, and the loss of SI may be accompanied by changes in the floral traits that promote or are associated with increased rates of selfing. For example, an increase in the rate of selfing at species and population level has been associated with lower pollen: ovule ratios (Cruden, 1977;Galloni et al, 2007;Jürgens et al, 2002), reduced investment in floral attractants (Lyons and Antonovics, 1991;Tang and Huang, 2007;Wyatt, 1984), reduced heterogamy (Takebayashi et al, 2006), and close anther-stigma separation (Holtsford and Ellstrand, 1992). In four Hypochaeris species, self-compatible species have smaller flower heads than self-incompatible species (Ortiz et al, 2006), and a high frequency of selfcompatible individuals in Leptosiphon jepsonii populations is associated with shorter corolla tubes and smaller corolla lobes (Goodwillie and Ness, 2005).…”

Genetic diversity in Leavenworthia populations with different inbreeding levels

“…L. stylosa and some populations of L. crassa are self-incompatible, while most L. crassa populations are self-compatible, with varying frequencies of self-fertilization, and L. uni£ora is uniformly highly inbreeding (Lloyd 1965;Rollins 1963;Solbrig & Rollins 1977;Lyons & Antonovics 1991). At least two independent comparisons between more outcrossing and more inbreeding populations are thus possible.…”

Breeding system and maternal success of a perennial hermaphrodite,Discaria americana(Rhamnaceae)

“…The occurrence of a lower frequency of single-seeded fruits in D. americana, than that expected if ovule survival were at random, thus seems to be consistent with the hypothesis of resource limitation. Excess of multiseeded fruits was also interpreted as evidence of resource limitation in Leavenworthia crassa (Lyons & Antonovics 1991).…”