The Quantitative Genetics of Fluctuating Asymmetry

Abstract

Fluctuating asymmetry (subtle departures from identical expression of a trait across an axis of symmetry) in many taxa is under stabilizing selection for reduced asymmetry. However, lack of reliable estimates of genetic parameters for asymmetry variation hampers our ability to predict the evolutionary outcome of this selection. Here we report on a study, based on analysis of variation within and between isofemale lines and of generation means (line-cross analysis), designed to dissect in detail the quantitative genetics of positional fluctuating asymmetry (PFA) in bristle number in natural populations of Drosophila falleni. PFA is defined as the difference between the two sides of the body in the placement or position of components of a meristic trait. Heritability (measured at 25ЊC) of two related measures of PFA were 13% and 21%, both of which differed significantly from zero. In contrast, heritability estimates for fluctuating asymmetry in the total number of anterior (0.7%) and transverse (2.4%) sternopleural bristles were smaller, not significant, and in quantitative agreement with previously published estimates. Heritabilities for bristle number (trait size) were considerably greater than that for any asymmetry measure. The experimental design controlled for the potentially confounding effects of common familial environment, and repeated testing revealed that PFA differences between lines were genetically stable for up to 16 generations in the laboratory at 25ЊC. We performed line cross analysis between strains at the extremes of the PFA distribution (highest and lowest values); parental strains, F 1 , F 1r (reciprocal), F 2 , backcross, and backcross reciprocal generations were represented. The inheritance of PFA was described best by additive and dominance effects localized to the X-chromosomes, whereas autosomal dominance effects were also detected. Epistatic, maternal, and cytoplasmic effects were not detected. The inheritance of trait size was notably more complex and involved significant autosomal additive, dominance, and epistatic effects; maternal dominance effects; and additive and dominance effects localized to the X-chromosomes. The additive genetic correlation between PFA and its associated measure of trait size was negative (Ϫ0.049), but not statistically significant, indicating that the loci contributing additive genetic effects to these traits are probably different. It is suggested that PFA may be a sensitive measure of developmental instability because PFA taps the ability of an organism to integrate interconnected developmental pathways.

Genetics of anthropometric asymmetry in an Indian endogamous population—Vaidyas

“…These low values are consistent with the heritability of other morphological asymmetric traits both in man (Bailit et al, 1970) as well as in different animal species (Leamy, 1986(Leamy, , 1997Polak and Starmer, 2001). On the other hand, some studies on man have found significant heritability values of asymmetric traits ranging between 20 and 45% (Livshits and Kobyliansky, 1989;Moller and Thornhill, 1997).…”

The quantitative genetics of sexual dimorphism: assessing the importance of sex-linkage

“…Model fitting is hierarchical, beginning with a simple model, such as the additive model (i.e., the expected mean phenotype of the crosses is a simple linear function of the relative contributions of the parental genomes such that the mean population values of the different crosses fall on a line connecting the two parental means, top graph, Figure 2), and increasing its complexity only if the model fails the joint-scaling test. In the presence of sex-linked effects, the expected mean phenotypic values change (Figure 2), and the line-cross analysis can be expanded to estimate sex-linked, epistatic and maternal effects (e.g., Carbonell et al, 1985;Barbato, 1991;Barbato and Vasilatos-Younken, 1991;Polak and Starmer, 2001;Huttunen and Aspi, 2003).…”

Epistasis and Dominance: Evidence for Differential Effects in Life-History Versus Morphological Traits

“…Adapted from Mather and Jinks (1982, life-history than morphological traits. In addition to those listed in the Appendix, the following papers were used in this analysis: Goud et al (1975), Ketata et al (1975), Arumugam and Muthukrishnan (1979), , Nanda et al (1981Nanda et al ( , 1982, Singh (1981), Bowman and Jones (1984), Singh et al ( , 1984Singh et al ( , 1987Singh et al ( , 1990, Melchinger et al (1986), Randhawa et al (1986), Verma and unus (1986), Garg et al (1987), Pawar et al (1988), Gupta and Labana (1989), Malhotra and Singh (1989), Singh and Nanda (1898), Subbaraman and Sree Rangasamy (1989), Virk et al (1989), Setiamihardja and Knavel (1990), Shinde and Deshmukh (1990), Kishor et al (1992), Wani and Zargar (1992), Ehdaie and Waines (1995), Pooni et al (1994), Tefera and Peat (1997), Ceballos et al (1998), L. L. , Carroll et al (2001), Galloway and Fenster (2001), Gilchrist and Partridge (2001), Khattak et al (2001), Polak and Starmer (2001). For the more specific questions concerning the magnitude of effects we used only six-parameter estimates (i.e., categories 2 and 3).…”