Outcrossing rates and inferred levels of inbreeding depression in gynodioecious Cucurbita foetidissima (Cucurbitaceae) (original) (raw)
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American Journal of Botany, 1999
Androdioecy, coexistence of hermaphrodites and males, is an extremely rare breeding system in angiosperms. In the present study, Schizopepon bryoniaefolius (Cucurbitaceae) was confirmed to be functionally androdioecious based on observations of floral and pollen morphology and bagging experiments. Six out of the 11 studied populations consisted of only hermaphrodites, while the other five populations were androdioecious and the frequencies of males were consistently lower than those of hermaphrodites (5.5-28.3%). To understand the consequences of an androdioecious breeding system, genetic variation was estimated using four polymorphic allozyme loci. The degree of genetic differentiation among 11 populations was high (G ST ϭ 0.688). Inbreeding coefficients (F IS) for all loci significantly deviated from zero. In particular, the F IS values averaged across the polymorphic loci in hermaphrodite populations were close to unity, suggesting that hermaphrodites are predominantly selfing in the absence of males. A significant negative correlation was found between the frequencies of males and inbreeding coefficients, indicating that outcrossing rates depend on the population sex ratio.
Reproductive biology of the andromonoecious Cucumis melo subsp. agrestis (Cucurbitaceae)
Annals of Botany, 2009
† Background and Aims Cucumis melo subsp. agrestis (Cucurbitaceae) is cultivated in many African regions for its edible kernels used as a soup thickener. The plant, an annual, andromonoecious, trailing-vine species, is of high social, cultural and economic value for local communities. In order to improve the yield of this crop, the first step and our aim were to elucidate its breeding system. † Methods Eight experimental pollination treatments were performed during three growing seasons to assess spontaneous selfing, self-compatibility and effects of pollen source (hermaphroditic vs. male flowers). Pollination success was determined by pollen tube growth and reproductive success was assessed by fruit, seed and seedling numbers and characteristics. The pollinator guild was surveyed and the pollination distance determined both by direct observations and by indirect fluorescent dye dispersal. † Key Results The species is probably pollinated by several Hymenoptera, principally by Hypotrigona para. Pollinator flight distances varied from 25 to 69 cm. No evidence for apomixis or spontaneous self-pollination in the absence of insect visitors was found. The self-fertility index (SFI ¼ 0) indicated a total dependence on pollinators for reproductive success. The effects of hand pollination on fruit set, seed number and seedling fitness differed among years. Pollen tube growth and reproductive success did not differ between self-and cross-pollinations. Accordingly, a high self-compatibility index for the fruit set (SCI ¼ 1. 00) and the seed number (SCI ¼ 0. 98) and a low inbreeding depression at all developmental stages (cumulative d ¼ 0. 126) suggest a high selfing ability. Finally, pollen origin had no effect on fruit and seed sets. † Conclusions This andromonoecious species has the potential for a mixed mating system with high dependence on insect-mediated pollination. The selfing rate through geitonogamy should be important.
Inbreeding Depression in Androdioecious Populations of Datisca glomerata (Datiscaceae)
American Journal of Botany, 1993
Several workers have suggested that the rarity of androdioecy (the presence of males and hermaphrodites in a breeding population) in nature is due to the large fitness gain required by male plants in order to be maintained by selection. As part of an ongoing investigation of this hypothesis, we tested the effects of selfing on fitness in functionally androdioecious populations of Datisca glomerata. We compared progeny from self-fertilizations, cross-fertilizations with pollen from male plants only, cross-fertilizations with pollen from hermaphrodite plants only, and open-pollinated flowers for several measures of progeny fitness including seed weight, germination rate, and seedling weight. Significant inbreeding depression was observed for androdioecious populations of D. glomerata for both seed and seedling weights. However, no significant differences were observed across treatments for seed germination percentages. The observation of significant levels of inbreeding depression in this study, combined with prior evidence of threefold greater pollen production by males, may at least partially account for the large fitness increase required by males to be maintained by selection.
Evolution, 2011
Hermaphroditic individuals can produce both selfed and outcrossed progeny, termed mixed mating. General theory predicts that mixed-mating populations should evolve quickly toward high rates of selfing, driven by rapid purging of genetic load and loss of inbreeding depression (ID), but the substantial number of mixed-mating species observed in nature calls this prediction into question. Lower average ID reported for selfing than for outcrossing populations is consistent with purging and suggests that mixed-mating taxa in evolutionary transition will have intermediate ID. We compared the magnitude of ID from published estimates for highly selfing (r > 0.8), mixed-mating (0.2 ≤ r ≥ 0.8), and highly outcrossing (r < 0.2) plant populations across 58 species. We found that mixed-mating and outcrossing taxa have equally high average lifetime ID (δ = 0.58 and 0.54, respectively) and similar ID at each of four life-cycle stages. These results are not consistent with evolution toward selfing in most mixed-mating taxa. We suggest that prevention of purging by selective interference could explain stable mixed mating in many natural populations. We identify critical gaps in the empirical data on ID and outline key approaches to filling them.
2018
In order to estimate the mean heterosis, mid parent heterosis and heterobeltiosis (HB), three diallel crossings of Cucurbita moschata were evaluated, each formed by six parents with three levels of inbreeding (S0, S1, S2). A randomized complete block experimental design was used with four replicates, arranged in split plots. The variables yield per plant (YPP) and average fruit weight (AFW) were analyzed. The hybrids between S1 or S2 inbred lines presented heterotic superiority regarding to those between S0 parents for the variables YPP and AFW. Likewise, the hybrids between S2 inbred lines reported heterotic superiority in comparison to those among S1 inbred lines, for such variables. The hybrids between S2 inbred lines that reported the highest expression levels of HB for YPP were P1xP3, P2xP6 and P1xP2, with values ranging between 131.42 and 98.24%; while the hybrids among S1 inbred lines that recorded the highest values of HB, for this same variable, were P3xP5 and P1xP5 with va...
Ecological and Evolutionary Consequences of Clonality for Plant Mating
Annual Review of …, 2010
Many flowering plants exhibit dual reproductive modes, producing both sexual and asexual offspring. The commonest form of asexual reproduction is clonal growth, in which vegetative modules (ramets) are produced by the parental genotype (genet). In plants, sexual and asexual reproduction usually occur simultaneously, and this can lead to allocation trade-offs and antagonism between reproductive modes. Our review considers the ecological and evolutionary consequences of functional interactions between clonal reproduction and pollination and mating. Clonal reproduction is commonly associated with mass flowering, restricted pollen dispersal, and geitonogamous self-pollination, processes that can result in inbreeding depression and pollen discounting. We review evidence for the correlated evolution of clonality and sexual systems, particularly self-incompatibility, and identify several floral mechanisms that function to reduce mating costs by limiting selfing and pollen discounting. We conclude by discussing the loss of sexuality in clonal plants and consider the genetic and environmental basis of sexual dysfunction. 193 Annu. Rev. Ecol. Evol. Syst. 2010.41:193-213. Downloaded from www.annualreviews.org by Universidad Nacional Autonoma de Mexico on 02/01/11. For personal use only. Click here for quick links to Annual Reviews content online, including: • Other articles in this volume • Top cited articles • Top downloaded articles • Our comprehensive search Further ANNUAL REVIEWS Ramet: the unit of clonal growth in plants, corresponding to a shoot that can be vegetative or reproductive 194 Vallejo-Marín · Dorken · Barrett Annu. Rev. Ecol. Evol. Syst. 2010.41:193-213. Downloaded from www.annualreviews.org by Universidad Nacional Autonoma de Mexico on 02/01/11. For personal use only. 196 Vallejo-Marín · Dorken · Barrett Annu. Rev. Ecol. Evol. Syst. 2010.41:193-213. Downloaded from www.annualreviews.org by Universidad Nacional Autonoma de Mexico on 02/01/11. For personal use only. G: number of genets N: number of plants (ramets)
Journal of Ecology, 2005
1 Male steriles (MS) must have a fitness advantage relative to hermaphrodites (H) if they are to be maintained in gynodioecious species. We report experiments in which we disentangle the relative contributions of seed size, inbreeding and maternal sex to the fitness advantage of male steriles in Plantago coronopus L. 2 Seed size effects were observed throughout growth experiments in the glasshouse and were reflected in all biomass measurements. In the field, seed size effects resulted in a fourfold increase in standardized seed production per initial buried seed after 2 years between small (mean weight = 0.13 mg) and large (0.20 mg) seeds. 3 Inbreeding depression, calculated from seed to seed was δ = 0.37 after one generation of selfing and δ = 0.93 after the second generation of selfing. Regression of log(1 − δ ) on inbreeding level suggested synergistic epistasis in fitness. 4 Even after taking into account the effects of seed size and inbreeding level, the offspring of a male sterile mother had a 16% advantage over a hermaphrodite, but this disappeared when the progeny sex ratio (the ratio of MS : H individuals among the offspring) was taken into account. 5 In the field, offspring of large seeds had both a higher overall incidence of flowering, and a higher probability of flowering in their first year, thus generating an extra cohort of individuals. The high inbreeding depression in fitness after two generations of selfing was also due to a very low incidence of flowering among the S2 individuals. Flowering probability therefore appears to be a critical trait in this system. 6 In the field, the contributions of seed size variation (15%) and inbreeding (9%) combine with 48% higher seed production to give a total fitness advantage of 70% of male steriles relative to hermaphrodites. This is probably sufficient for maintenance of gynodioecy under nuclear-cytoplasmic inheritance of male sterility. 7 Both inbreeding effects (as a consequence of the sexual system) and pleiotropic effects (of the genes coding for male sterility) play a role in the maintenance of gynodioecy in this species, with an apparently greater role for the latter.
Demographic Consequences of Pollen Limitation and Inbreeding Depression in a Gynodioecious Herb
International Journal of Plant Sciences, 2007
In a gynodioecious plant population, where female and hermaphroditic plants co-occur, females must produce more seeds or better-quality offspring than hermaphrodites to be maintained. Further, differences in the magnitude of pollen limitation and inbreeding depression between females and hermaphrodites may affect the relative fitness of the gender morphs and consequently population dynamics. We integrated demographic data into data on pollen limitation and inbreeding depression in a gynodioecious herb. Using a matrix model approach, we then examined the effects of pollen limitation and inbreeding depression on population growth rate and sex ratio. Hermaphrodites tended to contribute more to population growth rates than females. Because of the insensitivity of population growth rates to variation in annual fecundity, pollen limitation of either females or hermaphrodites had a negligible effect on population sex ratio. Inbreeding depression expressed simultaneously in three fitness components of the offspring produced by hermaphrodites reduced stochastic population growth rate and increased female frequency. Given that population growth rates are insensitive to fecundity transitions and that hermaphrodites have moderate selfing rates, our results suggest that inbreeding depression plays a larger role in the maintenance of females in gynodioecious populations than pollen limitation.