Data from: Expression of multiple sexual signals by fathers and sons in the East-Mediterranean barn swallow: Are advertising strategies heritable?

The level of expression of sexually selected traits is generally determined by genes, environment and their interaction. In species that use multiple sexual signals which may be costly to produce, investing in the expression of one sexual signal may limit the expression of the other, favoring the evolution of a strategy for resource allocation among signals. As a result, even when the expression of sexual signals is condition dependent, the relative level of expression of each signal may be heritable. We tested this hypothesis in the East-Mediterranean barn swallow (Hirundo rustica transitiva), in which males have been shown to express two uncorrelated sexual signals: red-brown ventral coloration, and long tail streamers. We show that variation in both signals may partially be explained by age, as well as by paternal origin (genetic father-son regressions), but that the strongest similarity between fathers and sons is the relative allocation towards one trait or the other (relative expression index), rather than the expression of the traits themselves. These results suggest that the expression of one signal is not independent of the other, and that genetic strategies for resource allocation among sexual signals may be selected for during the evolution of multiple sexual signals.性选择性状（sexually selected traits）的表达水平通常由基因、环境以及二者的交互作用共同决定。对于那些拥有多种产生成本高昂的性信号的物种而言，投入某一性信号的表达可能会限制另一性信号的表达，进而推动信号间资源分配策略的演化。因此，即便性信号的表达存在状态依赖性，各信号间的相对表达水平仍可能具有可遗传性。我们以东地中海家燕（*Hirundo rustica transitiva*）为对象检验了这一假说，该物种的雄性已被证实拥有两种无关联的性信号：红棕色腹羽色彩与长尾羽饰。我们的研究表明，两种信号的变异均可部分由年龄与父系起源（父子间的遗传回归分析）解释，但父子间最显著的相似性并非性状本身的表达水平，而是二者间的资源分配偏向——即相对表达指数（relative expression index）。上述结果表明，某一性信号的表达并非独立于另一信号，且在多重性信号的演化过程中，性信号间资源分配的遗传策略可能受到自然选择的青睐。