Telonis-Scott M, McIntyre L M, Wayne M L
Department of Zoology, University of Florida, Gainesville, FL, USA.
Genetica. 2005 Nov;125(2-3):211-22. doi: 10.1007/s10709-005-8549-4.
In Drosophila melanogaster, ovariole number and thorax length are morphological characters thought to be associated with fitness. Maximum daily egg production in females is positively correlated with ovariole number, while thorax length is correlated with male reproductive success and female fecundity. Though both traits are related to fitness, ovariole number is likely to be under stabilizing selection, while thorax length appears to be under directional selection. Current research has focused on examining the sources of variation for ovariole number in relation to fitness, with a view towards elucidating how segregating variation is maintained in natural populations. Here, we utilize a diallel design to explore the genetic architecture of ovariole number and thorax length in nine isogenic lines derived from a natural population. The full diallel design allows the estimation of general combining ability (GCA), specific combining ability (SCA), and also describes variation due to reciprocal effects (RGCA and RSCA). Ovariole number and thorax length differed with respect to their genetic architecture, reflective of the independent selective forces acting on the traits. For ovariole number, GCA accounted for the majority (67.3%) of variation segregating between the lines, with no evidence of reciprocal effects or inbreeding depression; SCA accounted for a small percentage (3.9%) of the variance, suggesting dominance variation; no reciprocal effects were observed. In contrast, for thorax length, the majority of the non-error variance was accounted for by SCA (17.9%), with only one third as much variance (6.2%) due to GCA. Interestingly, RSCA (nuclear-extranuclear interactions) accounted for slightly more variation (7.5%) than GCA in these data. Thus, genetic variation for thorax length is largely in accord with predictions for a fitness trait under directional selection: little additive genetic variation and substantial dominance variation (including a suggestion of inbreeding depression); while the mechanisms underlying the maintenance of variation for ovariole number are more complex.
在黑腹果蝇中，卵巢管数量和胸部长度是被认为与适合度相关的形态特征。雌性果蝇的最大日产卵量与卵巢管数量呈正相关，而胸部长度与雄性繁殖成功率和雌性繁殖力相关。尽管这两个性状都与适合度有关，但卵巢管数量可能受到稳定选择，而胸部长度似乎受到定向选择。目前的研究集中在研究与适合度相关的卵巢管数量变异来源，以期阐明自然种群中分离变异是如何维持的。在这里，我们利用双列杂交设计来探究来自自然种群的9个近交系中卵巢管数量和胸部长度的遗传结构。完整的双列杂交设计允许估计一般配合力（GCA）、特殊配合力（SCA），并且还描述了由于正反交效应（RGCA和RSCA）引起的变异。卵巢管数量和胸部长度在遗传结构上有所不同，这反映了作用于这些性状的独立选择力。对于卵巢管数量，GCA占品系间分离变异的大部分（67.3%），没有正反交效应或近交衰退的证据；SCA占方差的一小部分（3.9%），表明存在显性变异；未观察到正反交效应。相比之下，对于胸部长度，大部分非误差方差由SCA（17.9%）解释，由于GCA导致的方差仅为其三分之一（6.2%）。有趣的是，在这些数据中，RSCA（核-核外相互作用）解释的变异（7.5%）比GCA略多。因此，胸部长度的遗传变异在很大程度上符合对定向选择下适合度性状的预测：几乎没有加性遗传变异和大量显性变异（包括近交衰退的迹象）；而卵巢管数量变异维持的潜在机制则更为复杂。
