Epistasis for Fitness-Related Quantitative Traits in Arabidopsis thaliana Grown in the Field and in the Greenhouse

Abstract

The extent to which epistasis contributes to adaptation, population differentiation, and speciation is a long-standing and important problem in evolutionary genetics. Using recombinant inbred (RI) lines of Arabidopsis thaliana grown under natural field conditions, we have examined the genetic architecture of fitness-correlated traits with respect to epistasis; we identified both single-locus additive and two-locus epistatic QTL for natural variation in fruit number, germination, and seed length and width. For fruit number, we found seven significant epistatic interactions, but only two additive QTL. For seed germination, length, and width, there were from two to four additive QTL and from five to eight epistatic interactions. The epistatic interactions were both positive and negative. In each case, the magnitude of the epistatic effects was roughly double that of the effects of the additive QTL, varying from ÿ41% to 129% for fruit number and from ÿ5% to 14% for seed germination, length, and width. A number of the QTL that we describe participate in more than one epistatic interaction, and some loci identified as additive also may participate in an epistatic interaction; the genetic architecture for fitness traits may be a network of additive and epistatic effects. We compared the map positions of the additive and epistatic QTL for germination, seed width, and seed length from plants grown in both the field and the greenhouse. While the total number of significant additive and epistatic QTL was similar under the two growth conditions, the map locations were largely different. We found a small number of significant epistatic QTL 3 environment effects when we tested directly for them. Our results support the idea that epistatic interactions are an important part of natural genetic variation and reinforce the need for caution in comparing results from greenhouse-grown and fieldgrown plants.

Naturally segregating loci exhibit epistasis for fitness

“…Genetic effects are small relative to environmental effects, but on par with the effects of loci differentiating populations (e.g. comparing the portion of explained variance due to genetic effects relative to [4]). As this study focuses on only two loci, we cannot estimate the quantitative contribution of epistasis to fitness variation.…”

“…Additionally, the effect of a locus (gene) often depends on the environment experienced by the organism [2]. Field studies, using genetic lines containing known alleles, have shed light on the evolutionary significance of loci identified in controlled settings [3,4]. However, the common observation in mapping studies that genes interact with one another (i.e.…”

“…Epistasis is routinely invoked to explain reproductive isolation between species via Dobzhansky-Muller incompatibilities-interactions between heterospecific alleles that cause reduced fitness in hybrids [9,10]. Multiple studies suggest that epistasis contributes to fitness differences between populations within a species [11], including direct evidence from field assays [4,12]. However, evidence for epistasis in fitness for loci that are naturally segregating within populations is limited.…”

Genetic mapping of three quantitative trait loci for soybean aphid resistance in PI 567324

“…The epistatic effect for aphid resistance was only significant under the field conditions, indicating that the AA effect might be influenced by environment. Malmberg et al (2005) reported that epistatic interaction QTL for fitness-related traits can vary depending on different growth conditions from epistatic QTL analysis using RILs of Arabidopsis thaliana grown in the field and greenhouse. Besides, Zhuang et al (2002) suggested that the epistatic effects might be underestimated or go undetected due to increases in main effects in different environmental conditions.…”

Bin-based model construction and analytical strategies for dissecting complex traits with chromosome segment substitution lines

“…An additional restriction of conventional populations is the background noise that results from the complex epistatic interactions of different loci. A number of studies have shown that these interactions substantially contribute to the genetic control and evolution of complex traits [7,8]. However, many other studies that attempted to explore the genetic basis of complex traits ignored the possibility that loci interact [9].…”