Data from: Artificial selection on allometry: change in elevation but not slope

To what extent within-species (static) allometries constitute a constraint on evolution is the subject of a long-standing debate in evolutionary biology. A prerequisite for the constraint hypothesis is that static allometries are hard to change. Several studies have attempted to test this hypothesis with artificial-selection experiments, but their results remain inconclusive due to various methodological issues. Here, we present results from an experiment in which we selected independently on the slope and the elevation of the allometric relation between caudal-fin size and body size in male guppies (Poecilia reticulata). After three episodes of selection, the allometric elevation (i.e. intercept at constant slope) had diverged markedly between the lines selected to increase or decrease it, and showed a realized heritability of 50%. In contrast, the allometric slope remained unaffected by selection. These results suggest that the allometric elevation is more evolvable than the allometric slope, this latter representing a potential constraint on adaptive trait evolution. To our knowledge, this study is the first artificial-selection experiment that directly tests the evolvability of static allometric slopes.

种内（静态）异速生长（static allometry）在多大程度上构成进化约束，是进化生物学领域长期存在的争论议题。该约束假说的前提条件为，静态异速生长难以发生改变。已有多项研究尝试通过人工选择实验验证该假说，但受诸多方法学问题影响，相关结果始终未能达成定论。本研究报告了一项实验的结果：我们针对雄性孔雀鱼（Poecilia reticulata）尾鳍大小与体型间异速生长关系的斜率（slope）与截距（elevation）分别开展独立选择。经过三轮选择后，针对截距进行选择的各组品系间，异速生长截距（即固定斜率下的截距）出现了显著分化，其现实遗传力（realized heritability）达到50%。与之相反，异速生长斜率并未受到选择的影响。上述结果表明，异速生长截距的可进化性高于异速生长斜率，而后者可能对适应性性状进化构成潜在约束。据我们所知，本研究是首个直接验证静态异速生长斜率可进化性的人工选择实验。