Data from: An experimental test of the transmission−virulence trade-off hypothesis in a plant virus

The transmission–virulence trade-off hypothesis is one of the few adaptive explanations of virulence evolution, and assumes that there is an overall positive correlation between parasite transmission and virulence. The shape of the transmission–virulence relationship predicts whether virulence should evolve toward either a maximum or to an intermediate optimum. A positive correlation between each of these traits and within-host growth is often suggested to underlie the relationship between virulence and transmission. There are few experimental tests of this hypothesis; this study reports on the first empirical test on a plant pathogen. We infected Brassica rapa plants with nine natural isolates of Cauliflower mosaic virus and then estimated three traits: transmission, virulence, and within-host viral accumulation. As predicted by the trade-off hypothesis, we observed a positive correlation between transmission and virulence, suggestive of the existence of an intermediate optimum. We discovered the unexpected existence of two groups of within-host accumulation, differing by at least an order of magnitude. When accumulation groups were not accounted for, within-host accumulation was correlated neither to virulence nor transmission, although our results suggest that within each group these correlations exist.

传播-毒力权衡假说（transmission–virulence trade-off hypothesis）是少数针对毒力进化的适应性解释之一，该假说提出寄生虫的传播能力与毒力之间总体存在正相关。传播-毒力的关联形态可用于预测毒力的进化方向：究竟是趋向于最大值，还是收敛至某个中间最优值。学界普遍认为，毒力与传播之间的关联，其底层机制是这两个性状分别与宿主体内增殖（within-host growth）呈正相关。目前针对该假说的实验验证仍较为匮乏，本研究首次针对植物病原菌开展了该假说的实证检验。我们利用9株花椰菜花叶病毒（Cauliflower mosaic virus）的天然分离株接种芜菁（Brassica rapa）植株，随后对三个核心性状进行了测定：传播能力、毒力以及宿主体内病毒积累量（within-host viral accumulation）。正如权衡假说的预测，我们观测到传播能力与毒力之间呈正相关，这一结果暗示中间最优毒力值的存在。我们意外发现宿主体内病毒积累量可分为两个组别，二者的差异至少达到一个数量级。若未考虑病毒积累量的组别差异，宿主体内病毒积累量与毒力、传播能力均无关联；但研究结果表明，在每个组别内部，上述相关性均真实存在。