Abstract
Quantitative trait locus (QTL) mapping studies of Pacific three-spined sticklebacks (Gasterosteus aculeatus) have uncovered several genomic regions controlling variability in different morphological traits, but QTL studies of Atlantic sticklebacks are lacking. We mapped QTL for 40 morphological traits, including body size, body shape, and body armor, in a F2 full-sib cross between northern European marine and freshwater three-spined sticklebacks. A total of 52 significant QTL were identified at the 5% genome-wide level. One major QTL explaining 74.4% of the total variance in lateral plate number was detected on LG4, whereas several major QTL for centroid size (a proxy for body size), and the lengths of two dorsal spines, pelvic spine, and pelvic girdle were mapped on LG21 with the explained variance ranging from 27.9% to 57.6%. Major QTL for landmark coordinates defining body shape variation also were identified on LG21, with each explaining ≥15% of variance in body shape. Multiple QTL for different traits mapped on LG21 overlapped each other, implying pleiotropy and/or tight linkage. Thus, apart from providing confirmatory data to support conclusions born out of earlier QTL studies of Pacific sticklebacks, this study also describes several novel QTL of both major and smaller effect for ecologically important traits. The finding that many major QTL mapped on LG21 suggests that this linkage group might be a hotspot for genetic determinants of ecologically important morphological traits in three-spined sticklebacks.
Highlights
Quantitative trait locus (QTL) mapping studies of Pacific three-spined sticklebacks (Gasterosteus aculeatus) have uncovered several genomic regions controlling variability in different morphological traits, but QTL studies of Atlantic sticklebacks are lacking
With the exception of two recent case studies, which focused on the genetic architecture of a set of correlated traits relating to body shape (Albert et al 2008; Rogers et al 2012), most of these studies have focused on the genetic architecture of a single trait or phenotype (e.g., Colosimo et al 2004)
Despite the potential effect of distorted segregation ratios on genetic linkage map construction and subsequent QTL mapping, all the markers were used in the following analyses because the mapping analysis was implemented in JoinMap using the independence logarithm of odds (LOD), which is not affected by segregation distortion (Van Ooijen 2006)
Summary
Quantitative trait locus (QTL) mapping studies of Pacific three-spined sticklebacks (Gasterosteus aculeatus) have uncovered several genomic regions controlling variability in different morphological traits, but QTL studies of Atlantic sticklebacks are lacking. The genetic bases of these phenotypic traits have been the focus of many QTL-mapping studies in the last decade (Peichel et al 2001; Colosimo et al 2004; Cresko et al 2004; Shapiro et al 2004; Kimmel et al 2005; Albert et al 2008; Kitano et al 2009; Greenwood et al 2011; Rogers et al 2012) These studies have identified several genes and genomic regions contributing to variation in quantitative traits and thereby provided important insights into the genetic mechanisms of morphological divergence and adaptation. Apart from adding new dimensions to the understanding of the genetic architecture of phenotypic traits in the three-spined stickleback, our findings provide insights into the distribution of QTL effect sizes in a number of ecologically important morphological traits
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