Department of Ecology and Evolution, University of Lausanne, Biophore, Lausanne, Switzerland.
Mol Biol Evol. 2011 Apr;28(4):1381-92. doi: 10.1093/molbev/msq322. Epub 2010 Dec 20.
Ants provide remarkable examples of equivalent genotypes developing into divergent and discrete phenotypes. Diploid eggs can develop either into queens, which specialize in reproduction, or workers, which participate in cooperative tasks such as building the nest, collecting food, and rearing the young. In contrast, the differentiation between males and females generally depends upon whether eggs are fertilized, with fertilized (diploid) eggs giving rise to females and unfertilized (haploid) eggs giving rise to males. To obtain a comprehensive picture of the relative contributions of gender (sex), caste, developmental stage, and species divergence to gene expression evolution, we investigated gene expression patterns in pupal and adult queens, workers, and males of two species of fire ants, Solenopsis invicta and S. richteri. Microarray hybridizations revealed that variation in gene expression profiles is influenced more by developmental stage than by caste membership, sex, or species identity. The second major contributor to variation in gene expression was the combination of sex and caste. Although workers and queens share equivalent diploid nuclear genomes, they have highly distinctive patterns of gene expression in both the pupal and the adult stages, as might be expected given their extraordinary level of phenotypic differentiation. Overall, the difference in the proportion of differentially expressed genes was greater between workers and males than between workers and queens or queens and males, consistent with the fact that workers and males share neither gender nor reproductive capability. Moreover, between-species comparisons revealed that the greatest difference in gene expression patterns occurred in adult workers, a finding consistent with the fact that adult workers most directly experience the distinct external environments characterizing the different habitats occupied by the two species. Thus, much of the evolution of gene expression in ants may occur in the worker caste, despite the fact that these individuals are largely or completely sterile. Analyses of gene expression evolution revealed a combination of positive selection and relaxation of stabilizing selection as important factors driving the evolution of such genes.
蚂蚁为我们提供了一个很好的例子，证明具有相同基因型的个体可以发育成截然不同的表型。二倍体的卵可以发育成专门繁殖的蚁后，或者参与合作任务的工蚁，如筑巢、收集食物和育幼。相比之下，雌雄个体的分化通常取决于卵是否受精，受精卵（二倍体）发育成雌性，未受精卵（单倍体）发育成雄性。为了全面了解性别、职型、发育阶段和物种分化对基因表达进化的相对贡献，我们研究了两种红火蚁，即红火蚁和红火蚁，的蛹和成虫蚁后的、工蚁和雄蚁的基因表达模式。微阵列杂交显示，基因表达谱的变化更多地受到发育阶段的影响，而不是职型、性别或物种身份的影响。导致基因表达变化的第二个主要因素是性别和职型的组合。虽然工蚁和蚁后具有相同的二倍体核基因组，但它们在蛹和成虫阶段的基因表达模式都非常独特，这与它们表现出的非凡的表型分化水平是一致的。总的来说，工蚁和雄蚁之间差异表达基因的比例差异大于工蚁和蚁后或蚁后和雄蚁之间的差异，这与工蚁和雄蚁既没有性别也没有生殖能力的事实是一致的。此外，种间比较显示，基因表达模式的最大差异发生在成年工蚁中，这一发现与成年工蚁最直接地经历了两种不同栖息地所特有的不同外部环境的事实是一致的。因此，尽管这些个体基本上或完全不育，但蚂蚁的基因表达进化的大部分可能发生在工蚁职型中。对基因表达进化的分析揭示了正选择和稳定选择放松的结合是驱动这些基因进化的重要因素。
