Amplified fragment length polymorphism mapping of quantitative trait loci for malaria parasite susceptibility in the yellow fever mosquito Aedes aegypti

Abstract

The yellow fever mosquito Aedes aegypti has been the subject of extensive genetic research due to its medical importance and the ease with which it can be manipulated in the laboratory. A molecular genetic linkage map was constructed using 148 amplified fragment length polymorphism (AFLP) and six single-strand conformation polymorphism (SSCP) markers. Eighteen AFLP primer combinations were used to genotype two reciprocal F2 segregating populations. Each primer combination generated an average of 8.2 AFLP markers eligible for linkage mapping. The length of the integrated map was 180.9 cM, giving an average marker resolution of 1.2 cM. Composite interval mapping revealed a total of six QTL significantly affecting Plasmodium susceptibility in the two reciprocal crosses of Ae. aegypti. Two common QTL on linkage group 2 were identified in both crosses that had similar effects on the phenotype, and four QTL were unique to each cross. In one cross, the four main QTL accounted for 64% of the total phenotypic variance, and digenic epistasis explained 11.8% of the variance. In the second cross, the four main QTL explained 66% of the variance, and digenic epistasis accounted for 16% of the variance. The actions of these QTL were either dominance or underdominance. Our results indicated that at least three new QTL were mapped on chromosomes 1 and 3. The polygenic nature of susceptibility to P. gallinaceum and epistasis are important factors for significant variation within or among mosquito strains. The new map provides additional information useful for further genetic investigation, such as identification of new genes and positional cloning.

Figure 1.—

AFLP-based linkage map of Ae. aegypti and QTL locations for the susceptibility to the malaria parasite P. gallinaceum detected in two reciprocal F₂ intercrosses. The numbers on the left side of each linkage group are genetic distances in Kosambi centimorgans. AFLP markers are designated following Zhong et al. (2003). The SSCP markers are indicated by italics. With underlined markers, the dominant allele was descended from the RED strain while with the markers without underlining, the dominant allele was descended from the MOYO-R strain.

Figure 2.—

Frequency distribution of the number of P. gallinaceum oocysts in two F₂ segregating Ae. aegypti populations derived from pairwise mating between RED and MOYO-R strains. R5-5 represents an F₂ segregating population from a cross between a RED female and a MOYO-R male, while M7-7 represents a cross between a MOYO-R female and a RED male.

Figure 3.—

Composite interval mapping of the susceptibility to the malaria parasite P. gallinaceum in Ae. aegypti. Cross R5-5 represents an F₂ segregating population from a cross between a RED female and a MOYO-R male, while M7-3 represents a cross between a RED male and a MOYO-R female. Significance thresholds are indicated by dashed horizontal lines, with LOD = 3.0 (genomewide P < 0.001) as determined by 1000 permutations of our mapping data (Churchill and Doerge 1994).