Identification of major and minor QTL for ecologically important morphological traits in three-spined sticklebacks (Gasterosteus aculeatus)

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.

Keywords: Gasterosteus aculeatus; QTL; body shape; genetic linkage map; morphology.

Figure 1

Landmark locations for body shape and metric and meristic traits. Dotted outlines depict the lateral plates present in marine populations but reduced in freshwater populations. The traits and landmarks are described in the main text. Nplate, number of lateral plates; Pgir, pelvic girdle length; Pspi, pelvic spine length; D1st, length of the first dorsal spine; D2nd, length of the second dorsal spine.

Figure 2

A genome-wide consensus linkage map of G. aculeatus and the significant quantitative trait loci detected for phenotypic traits. Traits are divided into body size (centroid size), body shape (landmark coordinates, X/Y), and armor traits with different colors. See Figure 1 for trait abbreviations. The locations of two genes, Eda for lateral plate number and Pitx1 for pelvic development, are shown in orange. Eda includes Stn380, and the location of Pitx1 is below Stn82. Asterisks indicate markers with significantly distorted segregation ratios (*P < 0.05; **P < 0.01).