Mixed mating model

Abstract: ▪ Abstract Mixed mating, in which hermaphrodite plant species reproduce by both self- and cross-fertilization, presents a challenging problem for evolutionary biologists. Theory suggests that inbreeding depression, the main selective factor opposing the evolution of selfing, can be purged with self-fertilization, a process that is expected to yield pure strategies of either outcrossing or selfing. Here we present updated evidence suggesting that mixed mating systems are frequent in seed plants. We outline the floral and pollination mechanisms that can lead to intermediate outcrossing, review the theoretical models that address the stability of intermediate outcrossing, and examine relevant empirical evidence. A comparative analysis of estimated inbreeding coefficients and outcrossing rates suggests that mixed mating often evolves despite strong inbreeding depression. The adaptive significance of mixed mating has yet to be fully explained for any species. Recent theoretical and empirical work suggests that...

Abstract: A mixed mating model for many unlinked loci is described. A procedure for estimation of the model parameters (outcrossing rate and gene frequencies), based on a multilocus maximum likelihood equation, is discussed and analyzed for bias, variance, and robustness. Genotypic data from families of known or unknown maternal parentage, or data from progenies of known maternal parentage, are used for estimation. The procedure is applicable to dominant or co-dominant Mendelian genes with two or three alleles per locus, and should be particularly useful in studies where the effort in scoring more loci is less than the effort in scoring more progeny. Variances of the multilocus estimates of outcrossing rate and pollen pool gene frequencies decrease when more loci are included in the estimation. Monte Carlo simulations showed the estimates to be unbiased when model assumptions are not violated, but the bias introduced by various violations is reduced when more loci are included in the estimate. Often the variance of a three or four locus estimate closely approaches the minimum variance possible (the variance of an estimate using infinitely many loci), setting a practical limit to the number of loci needed for a nearly minimum variance estimate. An example from some work on Limnanthes is presented to illustrate the use of multilocus model and its fit to data from natural populations.

Abstract: Following principles used by A. J. Bateman, we identify the relationship between fecundity and mating success as the central feature in the operation of mating systems. Using selection theory from the field of quantitative genetics, we define the sexual selection gradient as the average slope of the relationship between fecundity and mating success and show how it can be estimated from data. We argue that sexual selection gradients are the key to understanding how the intensity of sexual selection is affected by mate provisioning, parental investment, and sex ratio.

Abstract: Previous reviews of plant outcrossing rate survey data have agreed that predominant selfing and predominant outcrossing are alternative stable states of mating system evolution. We reanalyzed the most recent data and plot outcrossing rates as a continuous variable rather than as a class variable. Wind-pollinated species are indeed bimodal. However, the shape of the distributions for animal-pollinated species reveals that intermediate rates of outcrossing are common (49% of species fall between 20% and 80% outcrossing). Consequently, we suggest that mating system is best considered a continuous rather than a discrete character of plant populations.