Akimoto Shin-ichi
Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
Evolution. 2006 Jan;60(1):77-86.
Trade-offs are potentially common among two or more traits whose development is dependent on the same resources. To detect genetic trade-offs, the techniques of quantitative genetics, pedigree analyses, and selection experiments have been used. This study demonstrates genetically based trade-offs between gonads and appendages in hatched larvae of the aphid Prociphilus oriens by focusing on enlarged variance among the families of selfed progeny. The selfed and outbred families were compared in respect to the size of morphological traits, gonad volume, and hatch dates as well as egg volume. Selfing not only increased the among-family variance component in all larval traits examined, but it also increased the mean size of all the morphological traits significantly. In contrast, gonad volume, a fitness component, was reduced with selfing. Calculation of the allometry (log-transformed regression) of larval traits to egg volume indicated that in the outbred group, morphological traits grew slowly relative to egg volume with slopes below 0.25, whereas gonads exhibited isometric growth. With selfing, most morphological traits had significantly steeper slopes, whereas the slope for gonads was greatly decreased. When the effect of egg volume was statistically removed from the means of selfed families, significant negative correlation was detected between the adjusted means of gonad volume and those of tibia length. This result suggests genetic trade-offs between gonad volume and tibia length. Thus, the evidence implies that at the loci governing the development of appendages, the dominant alleles function to canalize the development of tibiae into an optimal size, irrespective of egg volume. It is hypothesized that increased homozygosity of the deleterious recessive alleles reduced gonad volume through increasing the resource allocation to tibiae. The hypothesis of the gonad-appendage trade-off could be applied to explain the phenotypic evolution in some aphid species.
在两个或更多其发育依赖于相同资源的性状之间，权衡可能很常见。为了检测遗传权衡，人们使用了数量遗传学、系谱分析和选择实验等技术。本研究通过关注自交后代家系间增大的方差，证明了蚜虫东方原毛管蚜孵化幼虫的性腺与附肢之间存在基于遗传的权衡。对自交和杂交家系在形态性状大小、性腺体积、孵化日期以及卵体积方面进行了比较。自交不仅增加了所检测的所有幼虫性状的家系间方差成分，还显著增加了所有形态性状的平均大小。相比之下，作为适合度组成部分的性腺体积随着自交而减小。对幼虫性状与卵体积进行异速生长计算（对数转换回归）表明，在杂交组中，形态性状相对于卵体积生长缓慢，斜率低于0.25，而性腺呈现等速生长。自交时，大多数形态性状的斜率明显更陡，而性腺的斜率则大幅下降。当从自交家系的均值中统计去除卵体积的影响后，在性腺体积的调整均值与胫骨长度的调整均值之间检测到显著的负相关。这一结果表明性腺体积与胫骨长度之间存在遗传权衡。因此，有证据表明，在控制附肢发育的基因座上，显性等位基因的作用是将胫骨的发育引导至最佳大小，而与卵体积无关。据推测，有害隐性等位基因纯合度的增加通过增加对胫骨的资源分配而减少了性腺体积。性腺 - 附肢权衡的假说可用于解释某些蚜虫物种的表型进化。
