EVOLUTIONARY QUANTITATIVE GENETICS: HOW LITTLE DO WE KNOW?

“Such models are recommended as best practice for studying phenotypic plasticity (Nussey et al. 2007) and genotype-by-environment interactions (e.g., Barton and Turelli 1989; Charmantier and Garant 2005; Kruuk et al. 2008) including tolerance (Graham et al. 2011; Kause 2011; Doeschl-Wilson et al.…”

“We kept our population sizes low to keep the model conservative (i.e., limiting for adaptation) and also faster-running, but compensated for this by assuming a mutation rate on the upper boundary of values reported in the literature, 10−5 per QTL per generation (Barton & Turelli, 1989).”

“Long-term changes depend on genetic facts about which we know almost nothing ( Barton & Turelli, 1989 ).”

“…tradeoffs between different types of heat resistance (Hoffmann et al., 1997; Berrigan & Hoffmann, 1998) could influence the outcome of selection (Barton & Turelli, 1989) and may explain the decreased heat resistance observed in our laboratory evolution experiment where fitness is shaped by many…”

“While much of the previous literature has focused on mechanisms for maintenance of genetic variance (Barton and Turelli 1989; Barton and Keightley 2002; Zhang et al. 2004), we also need to understand what maintains the existing levels of environmental variability.”

“…shown that the traits considered polygenic by more traditional studies might in fact be influenced by few quantitative trait loci (QTL) (reviewed in Barton and Turelli , 1989; Orr and Coyne, 1992; Mitchell-Olds, 1995), including Drosophila song (Williams et al, 2001) so here we ask whether there…”

“For instance, heterozygote advantage is essentially selection for genetic diversity and will maintain variation, including in species with nonoverlapping generations (Barton and Turelli 1989) and in many scenarios for species with overlapping generations (Ellner and Hairston 1994, Hedrick 2005).”

“the maintenance of genetic variation [6], the evolution of”

“traits makes the prediction of their response to selection immensely intricate, even under the simplest assumptions (e.g. additivity, equal eects of an allele on the trait, and linkage equilibrium) (Barton and Turelli 1989; Keightley and Hill 1990; Turelli and Barton 1994). Most traits seem to be under some form of st…”

“The 1980s were an era of debate in the theoretical quantitative genetics community between two competing schools of thought.(1) The question of interest was ‘‘What is the nature of genetic variation contributing to complex traits?’’ On one hand there was the infinitesimal school,(2) which argued that complex traits we…”

“Even earlier, in 1989, Barton and Turelli, two of the most prominent theoreticians in the field, published a rather skeptical article entitled: ‘Evolutionary quantitative genetics: how little do we know?’ The answer they arrived at – that in fact, we know very little about what we would like to know – has not changed…”

“Such a roadmap has been developed by several workers including Bulmer (1972), Barton and Turelli (1989), and Bürger (2000), and we follow this direction here to understand the rapid evolutionary dynamics of a single quantitative trait under stabilizing selection (Jain and Stephan 2015, 2017).”

“…developmental constraints has in the past primarily focused on genetic constraints, in particular on the potential of genetic covariation due to linkage disequilibrium or pleiotropy to constrain evolution (e.g. Barton & Turelli 1989, Kirkpatrick & Lofsvold 1992, Futuyma et al. 1995, Connor 2012).”

“Sample size estimates were based on the assumption that all QTLs have equal and additive effects (Fisher, 1918; Barton and Turelli, 1989).”

“However, the effect of stress on genetic variation is under dispute (Barton & Turelli, 1989) as the*Correspondence.”

“dtd" [ ]> Understanding the pleiotropic effects of adaptive mutations is central to comprehending evolutionary chang”

“Several forms of selection, particularly stabilizing selection, should deplete genetic variation (Barton and Turelli 1989; Roff 1997; Bürger 2000; Barton and Keightley 2002).”

“Because it is usually thought that temporarily fluctuating selection on phenotype can hardly maintain genetic variance (Hedrick 1986; Barton and Turelli 1989; but see Ellner and Hairston 1994), more studies are required to determine how colour polymorphism is maintained in species like the ladybird…”

“This assumption has long been the basis of most studies of quantitative genetic modeling (Lande, 1975; Barton and Turelli, 1989; Barton, 1990).”

“For example, Bull (1987) states that ‘‘genetic variance is not encouraged by fluctuating selection’’; Barton and Turelli (1989) state that ‘‘fluctuations in phenotypic fitnesses will not easily maintain variation’’ and that such fluctuations have only slight effects on the level of variation maintained by mutationsele…”

“Our estimates of , Vm and Vg do not alter the conclusion that simple mutation – stabilizing selection models for either direct or apparent stabilizing selection cannot maintain the observed amounts of segregating genetic variation with the observed mutational input and strong selection: the mutational variance is too…”

“Identification of QTLs with minor effects on complex traits remains a difficult issue in quantitative genetics [29].”

“This kind of information is vital for evaluating various models of the maintenance of segregating variation and adaptation ( Barton & Turelli, 1989; Orr, 1998; Agrawal et al., 2001).”

“…parameters, most importantly, the number of loci underlying mean trait values and reaction norms, the distribution of effects among these loci and the genomic organization of such genes (Barton & Turelli, 1989; Charlesworth, 1990; Clark & Koehn, 1991; Feder & Watt, 1991; Mitchell-Olds, 1995).”

“In general, exact predictions about the evolution of quantitative traits assuming Mendelian inheritance cannot be made unless a large amount of detailed information about the genetic basis of the trait is available ( Barton & Turelli, 1989 ).”

“Our knowledge of the actual genetics of quantitative traits is very limited (Barton and Turelli, 1989) genetic details may matter (Turelli, 1988) and simple expectations may be wrong.”

“…of variation in sexual signaling traits under strong stabilizing or directional selection remains a persistent problem in evolutionary biology (Barton and Turelli 1989; Barton and Keightley 2002; Blows and Hoffmann 2005) as strong directional selection or stabilizing selection depletes…”

“Analytical and simulation studies (Lande 1980; Turelli 1988; Barton and Turelli 1989; Reeve 2000; Jones et al. 2003, 2004) resulted in formulation of conditions promoting stability of G structure.”

“…lead to the erosion of genetic variation, whereas disruptive selection can contribute to an increase in genetic variation if the population continues to straddle the nadir of the fitness surface (Lande and Arnold 1983; Barton and Turelli 1989; Barton and Keightley 2002; John- son and Barton 2005).”

“This argument is consistent with the proposal that genetic variance could be maintained in natural populations by temporal changes in selective pressures (Turelli, 1988; Barton and Turelli, 1989; Bulmer, 1989).”

“On the other hand, genotypes that confer higher fitness with respect to some fitness traits may have reduced fitness for others (Allendorf and Leary 1986), probably due to antagonistic pleiotropy in expression of genes affecting fitness (Service and Rose 1985; Barton and Turelli 1989 ).”

“Explanations for the maintenance of quantitative variation and predictions of the limits to selection depend on the basis of variation (Barton and Turelli 1989; Hill and Caballero 1992).”

“Hence, on longer evolutionary time scales, and in large populations, mutational input and selection are the main factors of change due to changing allele frequencies (e.g. Barton & Turelli, 1989; Arnold et al., 2008).”

“…could be responsible for the maintenance of genetic variation in the different early lifehistory traits through antagonistic selection (Rose, 1982; Barton & Turelli, 1989; Roff, 1992; Stearns, 1992) and, therefore, would underlie the maintenance of genetic polymorphism in the early life-history…”

“Lobelia cardinalis (Devlin 1989) and L. siphilitica (Beaudoin Yetter 1989) can produce clonal offshoots, but we attempted to sample fruits from only one ramet per genet.”

“The inability of simple models to reproduce coexistence was noted in the specific contexts of S. pneumoniae [15,18,19] and Staphylococcus aureus [20] and is an instance of the more general problem of the maintenance of genetic diversity in the face of selection in evolutionary biology [21].”

“When traits have an oligogenetic basis rather than matching the theoretical construct of the Gaussian infinitesimal model, changes in the G-matrix are expected during evolution (Barton & Turelli, 1987; Turelli, 1988; Barton & Turelli, 1989).”

“…genetics theory (Lynch and Walsh 1998), especially for empiricists, compared to single-locus population genetics, as mutation-selection balance was thought to solve that problem for quantitative traits under some simplifying assumptions (Lande 1976; but see Turelli 1984, Barton and Turelli 1989).”

“Alternatively, is the bulk of standing genetic variation for complex traits due to modesteffect intermediate frequency alleles maintained by some form of balancing selection (reviewed by Barton and Turelli 1989; Barton and Keightley 2002)?”

“This spatiotemporal variation in the intensity or direction of selection is commonly proposed as a primary mechanism responsible for the maintenance of trait variation both within and between populations (Barton and Turelli 1989; Merilä et al. 2001; Brooks 2002).”

“The relationship between phenotypic variable and the intensity of stabilizing selection has been the subject of much theoretical debate (Bulmer 1985; Barton and Turelli 1989) and has rarely been tested directly (West and Herre 1998).”

“Whereas evolutionary geneticists identify no fewer than seven mechanisms that can, in theory, maintain (additive) genetic variance within a population ( Barton & Turelli, 1989; Roff, 1997; Lynch & Walsh, 1998), most investigations of sexually selected traits have concentrated on mutation-selection balance, genetic tra…”

“An enduring problem in evolutionary biology has been explaining the maintenance of genetic variation in the face of directional selection (Barton and Turelli 1989).”

“…to additive variance means that the relative contribution of dominance variance to conversion is high and thus that conversion of variance will not play a significant role in adaptive evolution (eg Barton and Turelli, 1989, 2004; Willis and Orr, 1993; Coyne et al, 1997; López-Fanjul et al, 2004).”

“Second, negative genetic correlations between pairs of traits are a widely appreciated potential constraint on the evolution of life history traits and other characters (Via & Lande, 1985; Barton & Turelli, 1989).”

“One hypothesis states that the introduction of new alleles through mutation will counterbalance the erosion of genetic variation resulting from purifying selection (Hedrick 1986, Barton and Turelli 1989).”

“In addition to predicting short-term responses to selection, quantitative genetic models of long-term phenotypic evolution are also potentially applicable to the analysis of physiological traits (7–9, 50, 82, 91, 107), although these models are premised on controversial assumptions about the constancy of genetic param…”

“…fecundity, growth, or survival in resistant individuals (Carriere et al. 1994; Mauricio and Rausher 1997; Janmaat and Myers 2005), and in laboratory selection experiments, limits to evolution are often reached due to negative pleiotropic effects of alleles under selection (Barton and Turelli 1989).”