A novel mating system analysis for modes of self-oriented mating applied to diploid and polyploid arctic Easter daisies (Townsendia hookeri)

Abstract

We have developed a new model for mating system analysis, which attempts to distinguish among alternative modes of self-oriented mating within populations. This model jointly estimates the rates of outcrossing, selfing, automixis and apomixis, through the use of information in the family structure given by dominant genetic marker data. The method is presented, its statistical properties evaluated, and is applied to three arctic Easter daisy populations, one consisting of diploids, the other two of tetraploids. The tetraploids are predominantly male sterile and reported to be apomictic while the diploids are male fertile. In each Easter daisy population, 10 maternal arrays of six progeny were assayed for amplified fragment length polymorphism markers. Estimates, confirmed with likelihood ratio tests of mating hypotheses, showed apomixis to be predominant in all populations (ca. 70%), but selfing or automixis was moderate (ca. 25%) in tetraploids. It was difficult to distinguish selfing from automixis, and simulations confirm that with even very large sample sizes, the estimates have a very strong negative statistical correlation, for example, they are not independent. No selfing or automixis was apparent in the diploid population, instead, moderate levels of outcrossing were detected (23%). Low but significant levels of outcrossing (2-4%) seemed to occur in the male-sterile tetraploid populations; this may be due to genotyping error of this level. Overall, this study shows apomixis can be partial, and provides evidence for higher levels of inbreeding in polyploids compared to diploids and for significant levels of apomixis in a diploid plant population.

Study of quantitative genetics of gum arabic production complicated by variability in ploidy level of Acacia senegal (L.) Willd

“…Reproduction with only few male donors and perhaps even self-pollinations and apomixes as suggested for polyploid Ngane is in line with the general observation of selfing and apomixis often being associated with polyploidy (Hörandl 2010). Polyploids are reported to exhibit higher rates of self-fertilization than related diploid species and 99 % of the known apomictic plants are reported to be polyploids (Thompson and Ritland 2006). As newly formed polyploids in the beginning will represent minority cytotypes in the nature, uniparental mating provided by self-fertilization and apomixis is likely to increase the ability of newly formed polyploids to establish in an environment mainly represented by diploid plants (Husband 2000) and persist because backcrossing with the parental diploid species often results in sterile progeny (Stebbins 1971;Grant 1981).…”

Quantifying inbreeding in natural populations of hermaphroditic organisms

“…Dominance imposes PAA as the only possible method for estimating the selfing rate with AFLPs. Very few studies have been published to date (for example, Thompson and Ritland, 2006).…”

“…Formal maximum likelihood estimation was initiated by Fyfe and Bailey (1951), and later extended to co-dominant loci (allozymes) by RW Allard and associates (for example, Brown and Allard, 1970;Clegg et al, 1978). A key insight was to incorporate multilocus information (Ritland and Jain, 1981;Shaw et al, 1981), and a good part of subsequent developments of the maximum likelihood method is due to the continuous efforts of Ritland (Ritland, 1986(Ritland, , 1989(Ritland, , 2002Thompson and Ritland, 2006), and others (for example, Schoen and Clegg, 1986). This was paralleled by a marked increase in the number of studies estimating the selfing rate in natural plant populations (see Schemske and Lande, 1985;Goodwillie et al, 2005).…”

“…Extensions were developed for tetraploids with tetrasomic inheritance and no double reduction at meiosis (Murawski et al, 1994;Thompson and Ritland, 2006), automixis and apomixis (Thompson and Ritland, 2006), and dominant markers (Ritland, 1990b;Thompson and Ritland, 2006). S can be estimated at different sampling levels, for example individuals and/or families (Ritland and El Kassaby, 1985).…”

A maximum-likelihood estimation of pairwise relatedness for autopolyploids

“…However, diploid models cannot be applied to polyploids that display polysomic inheritance, that is, autopolyploids. Thus, few models apply directly to autopolyploids (cf Murawski et al, 1994;Thompson and Ritland, 2006). Here we focus on polyploids displaying polysomic inheritance, and introduce a maximum-likelihood method for estimating coefficients of relatedness for co-dominant markers in panmictic populations.…”