Host responses in life-history traits and tolerance to virus infection in Arabidopsis thaliana

Abstract

Knowing how hosts respond to parasite infection is paramount in understanding the effects of parasites on host populations and hence host-parasite co-evolution. Modification of life-history traits in response to parasitism has received less attention than other defence strategies. Life-history theory predicts that parasitised hosts will increase reproductive effort and accelerate reproduction. However, empirical analyses of these predictions are few and mostly limited to animal-parasite systems. We have analysed life-history trait responses in 18 accessions of Arabidopsis thaliana infected at two different developmental stages with three strains of Cucumber mosaic virus (CMV). Accessions were divided into two groups according to allometric relationships; these groups differed also in their tolerance to CMV infection. Life-history trait modification upon virus infection depended on the host genotype and the stage at infection. While all accessions delayed flowering, only the more tolerant allometric group modified resource allocation to increase the production of reproductive structures and progeny, and reduced the length of reproductive period. Our results are in agreement with modifications of life-history traits reported for parasitised animals and with predictions from life-history theory. Thus, we provide empirical support for the general validity of theoretical predictions. In addition, this experimental approach allowed us to quantitatively estimate the genetic determinism of life-history trait plasticity and to evaluate the role of life-history trait modification in defence against parasites, two largely unexplored issues.

Figure 1. Relationship between growth (RW) and reproductive effort (IW) in Arabidopsis accessions.

Correlation between IW and RW for allometry group 1 (red) and allometry group 2 (blue) using mean accession values of mock-inoculated plants. Data are mean±standard error of RW and IW in g. The upper-right panel shows the frequency distribution of the IW/RW relationship of the 18 accessions, based in individual plant values.

Figure 2. Effect of CMV infection on life-history traits for the two allometric groups of accessions.

Effect of viral infection was estimated as the ratio between infected (i) and mock-inoculated (m) plants. Data are mean±standard errors of accession means.

Figure 3. Effects of CMV infection on growth/reproduction resource allocation of Arabidopsis accessions.

(A) Effect of infection on IW/RW relationship for allometry group 1. (B) Effect of infection on IW/RW relationship for allometry group 2. (C) Effect of infection on SW/(IW-SW) relationship for allometry group 1. (D) Effect of infection in SW/(IW-SW) relationship for allometry group 2. Relationship in infected plants (green) is compared with that of mock-inoculated plants of allometry group 1 (red) and 2 (blue). Data are mean values of each accession. RW, IW and (IW-SW) units are g.

Figure 4. Effect of viral infection on growth (GP) and reproductive (RP) period span of Arabidopsis accessions.

(A) Effect of CMV infection in GP period span estimated as GP_i/GP_m, where i and m denote infected and mock-inoculated plants, respectively. (B) Effect of CMV infection in RP period span estimated as described for (A). Data are mean values of accessions infected by each CMV isolates±standard errors. Asterisks indicate significant differences between mock-inoculated and infected plants (P<0.05). The effect of infection is shown for LS-CMV (green), Fny-CMV (blue) and De72-CMV (red). Accessions are divided into allometry groups 1 and 2.