What maintains mixed mating is an evolutionary enigma. Cleistogamy, the production of both potentially outcrossing chasmogamous, and obligately selfing cleistogamous flowers on the same individual plant, is an excellent system to study the costs of selfing. Inbreeding depression can prevent the evolution of greater selfing within populations, and heterosis in crosses between populations may further tip the balance in favor of outcrossing. Few empirical estimates of inbreeding depression and heterosis in the same system exist for cleistogamous species. We investigate the potential costs of selfing by quantifying inbreeding depression and heterosis in three populations of the cleistogamous perennialRuellia humilisNutt (Acanthaceae). We performed hand-pollinations to self, and outcross within and between populations, and measured seed number, germination, total flower production, and estimated cumulative fitness for the resulting progeny in a greenhouse experiment.We found moderate inbreeding depression for cumulative fitness (<30%) in two populations, but outbreeding depression for crosses within a third population (−26%). For between population crosses, there was weak to modest heterosis (11-47%) in two of the population combinations, but modest to strong outbreeding (−21 to −71%) depression in the other four combinations. Neither inbreeding depression nor heterosis was of sufficient magnitude to explain the continued production of CH flowers given the relative energetic advantage of CL flowers previously estimated for these populations. Outbreeding depression either within or between populations makes the maintenance of chasmogamous flowers even harder to explain. More information is needed on the genetic basis of cleistogamy in order to resolve this conundrum.

Freezing tolerance is likely to be an important adaptation for both natural populations and crop cultivars like winter wheat (Triticum aestivum L.). In the United States, winter wheat represents 80% of the total wheat production. Understanding the genetic basis of freezing tolerance in wheat furthers our knowledge of abiotic stress tolerance in plants and may inform breeding programs aimed at adjusting the level of freezing tolerance for a given region. We examined freezing tolerance in a 267-line panel of elite soft red winter wheat that has previously been used for genome-wide association study (GWAS) on agronomically important traits. We were specifically interested in determining the extent of genetic variation for freezing tolerance within the panel, what the genetic basis of that variation is, and if there are correlations between freezing tolerance and other agronomically important traits. We found significant variation in freezing tolerance among the lines, measured as survival through three total days at −8 ˚C. We performed a GWAS on freezing tolerance and identified 13 candidate loci, with nearby candidate genes involved in different functions potentially associated with freezing tolerance. In addition, we found significant correlations between freezing tolerance and seven previously published yield related traits. In summary, we found considerable variation in freezing tolerance in this panel that is associated with yield related traits. Thus, these lines may be useful for breeding programs seeking to optimize freezing tolerance for present and future climatic conditions. INTRODUCTIONWheat (Triticum aestivum L.) is one of the most important crops worldwide. It is cultivated in ∼200 million ha (http: //www.fao.org/faostat/en/#data/QC/visualize) (Zhao et al., 2013) and provided about 20% of all dietary calories consumed globally (