Genetic variation and covariation in floral allocation of two species of Schiedea with contrasting levels of sexual dimorphism

Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697, USA.
Evolution (Impact Factor: 4.61). 11/2010; 65(3):757-70. DOI: 10.1111/j.1558-5646.2010.01172.x
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ABSTRACT The evolution of sexual dimorphism depends in part on the additive genetic variance-covariance matrices within females, within males, and across the sexes. We investigated quantitative genetics of floral biomass allocation in females and hermaphrodites of gynodioecious Schiedea adamantis (Caryophyllaceae). The G-matrices within females (G(f)), within hermaphrodites (G(m)), and between sexes (B) were compared to those for the closely related S. salicaria, which exhibits a lower frequency of females and less-pronounced sexual dimorphism. Additive genetic variation was detected in all measured traits in S. adamantis, with narrow-sense heritability from 0.34-1.0. Female allocation and floral size traits covaried more tightly than did those traits with allocation to stamens. Between-sex genetic correlations were all <1, indicating sex-specific expression of genes. Common principal-components analysis detected differences between G(f) and G(m) , suggesting potential for further independent evolution of the sexes. The two species of Schiedea differed in G(m) and especially so in G(f) , with S. adamantis showing greater genetic variation in capsule mass and tighter genetic covariation between female allocation traits and flower size in females. Despite greater sexual dimorphism in S. adamantis, genetic correlations between the two sexes (standardized elements of B) were similar to correlations between sexes in S. salicaria.

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Available from: Diane R Campbell, Jul 25, 2014
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    • "Although cytoplasmic factors are responsible for male sterility in many plant species, we have no evidence to suggest the involvement of cytoplasmic factors in sex expression in Schiedea. Extensive inter-and intraspecific crosses (Weller et al., 2001; Sakai et al., 2008; Campbell et al., 2011) did not show female excesses in the progeny , a characteristic feature of crosses where cytoplasmic female-sterility factors are not matched by nuclear fertility-restoring factors. Hybrids between species of Schiedea are often highly fertile (Weller et al., 2001), indicating that natural hybridization could lead to transfer of male-sterility alleles from gynodioecious, subdioecious or dioecious species to hermaphroditic species. "
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    ABSTRACT: Hybrid zones may serve as bridges permitting gene flow between species, including alleles influencing the evolution of breeding systems. Using greenhouse crosses, we assessed the likelihood that a hybrid zone could serve as a conduit for transfer of nuclear male-sterility alleles between a gynodioecious species and a hermaphroditic species with very rare females in some populations. Segregation patterns in progeny of crosses between rare females of hermaphroditic Schiedea menziesii and hermaphroditic plants of gynodioecious Schiedea salicaria heterozygous at the male-sterility locus, and between female S. salicaria and hermaphroditic plants from the hybrid zone, were used to determine whether male-sterility was controlled at the same locus in the parental species and the hybrid zone. Segregations of females and hermaphrodites in approximately equal ratios from many of the crosses indicate that the same nuclear male-sterility allele occurs in the parent species and the hybrid zone. These rare male-sterility alleles in S. menziesii may result from gene flow from S. salicaria through the hybrid zone, presumably facilitated by wind pollination in S. salicaria. Alternatively, rare male-sterility alleles might result from a reversal from gynodioecy to hermaphroditism in S. menziesii, or possibly de novo evolution of male sterility. Phylogenetic analysis indicates that some species of Schiedea have probably evolved separate sexes independently, but not in the lineage containing S. salicaria and S. menziesii. High levels of selfing and expression of strong inbreeding depression in S. menziesii, which together should favour females in populations, argue against a reversal from gynodioecy to hermaphroditism in S. menziesii.
    Journal of Evolutionary Biology 01/2014; 27(2). DOI:10.1111/jeb.12312 · 3.23 Impact Factor
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    • "imorphic overall (Wyman and Rowe, unpublished results). By contrast, most studies that have measured sex-specific G matrices demonstrate that they are dimorphic (Holloway et al., 1993; Guntrip et al., 1997; Ashman, 2003; Jensen et al., 2003; Rolff et al., 2005; McGuigan & Blows, 2007; Sakai et al., 2007; Steven et al., 2007; Dmitriew et al., 2010; Campbell. Such et al. 2010; Lewis et al., 2011). Such differences are due to the fact that the multivariate formulation can take into account both the size of the genetic variance and how it is oriented between the sexes (Fig. 1). Previous authors have pointed out that g max will always explain more variance than any single univariate genetic variance by default "
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    ABSTRACT: Sexual differences are often dramatic and widespread across taxa. Their extravagance and ubiquity can be puzzling because the common underlying genome of males and females is expected to impede rather than foster phenotypic divergence. Widespread dimorphism, despite a shared genome, may be more readily explained by considering the multivariate, rather than univariate, framework governing the evolution of sexual dimorphism. In the univariate formulation, differences in genetic variances and a low intersexual genetic correlation (rMF) can facilitate the evolution of sexual dimorphism. However, studies that have analysed sex-specific differences in heritabilities or genetic variances do not always find significant differences. Furthermore, many of the reported estimates of rMF are very high and positive. When monomorphic heritabilities and a high rMF are present together, the evolution of sexual dimorphism on a trait-by-trait basis is severely constrained. By contrast, the multivariate formulation has greater generality and more flexibility. Although the number of multivariate sexual dimorphism studies is low, almost all support sex-specific differences in the G (variance-covariance) matrix; G matrices can differ with respect to size and/or orientation, affecting the response to selection differently between the sexes. Second, whereas positive values of the univariate quantity rMF only hinder positive changes in sexual dimorphism, positive covariances in the intersexual covariance B matrix can either help or hinder. Similarly, the handful of studies reporting B matrices indicate that it is often asymmetric, so that B can affect the evolution of single traits differently between the sexes. Multivariate approaches typically demonstrate that genetic covariances among traits can strongly constrain trait evolution when compared with univariate approaches. By contrast, in the evolution of sexual dimorphism, a multivariate view potentially reveals more opportunities for sexual dimorphism to evolve by considering the effect sex-specific selection has on sex-specific G matrices and an asymmetric B matrix.
    Journal of Evolutionary Biology 10/2013; 26(10):2070-80. DOI:10.1111/jeb.12188 · 3.23 Impact Factor
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    • "The more easily estimated matrix of phenotypic variances and covariances P can be used as a surrogate for G, especially in the case of high heritability morphological characters [1-4]. Comparisons between covariance matrices are carried out in the study of a wide array of evolutionary problems, such as the stability of G in the presence of selection and drift [5-7], the role of genetic constraints on determining evolutionary trajectories in adaptive radiations [8], the response of genetic architecture to environmental heterogeneity [9], the evolution of phenotypic integration [4,10], multi-character phenotypic plasticity [11] and sexual dimorphism [12,13]. "
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    ABSTRACT: Background Comparing the covariation patterns of populations or species is a basic step in the evolutionary analysis of quantitative traits. Here I propose a new, simple method to make this comparison in two population samples that is based on comparing the variance explained in each sample by the eigenvectors of its own covariance matrix with that explained by the covariance matrix eigenvectors of the other sample. The rationale of this procedure is that the matrix eigenvectors of two similar samples would explain similar amounts of variance in the two samples. I use computer simulation and morphological covariance matrices from the two morphs in a marine snail hybrid zone to show how the proposed procedure can be used to measure the contribution of the matrices orientation and shape to the overall differentiation. Results I show how this procedure can detect even modest differences between matrices calculated with moderately sized samples, and how it can be used as the basis for more detailed analyses of the nature of these differences. Conclusions The new procedure constitutes a useful resource for the comparison of covariance matrices. It could fill the gap between procedures resulting in a single, overall measure of differentiation, and analytical methods based on multiple model comparison not providing such a measure.
    BMC Evolutionary Biology 11/2012; 12(1):222. DOI:10.1186/1471-2148-12-222 · 3.37 Impact Factor
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