Data from: Heritable variation in maternally-derived yolk androgens, thyroid hormones and immune factors

Maternal reproductive investment can critically influence offspring phenotype, and thus these maternal effects are expected to be under strong natural selection. Knowledge on the extent of heritable variation in the physiological mechanisms underlying maternal effects is however limited. In birds, resource allocation to eggs is a key mechanism for mothers to affect their offspring and different components of the egg may or may not be independently adjusted. We studied the heritability of egg components and their genetic and phenotypic covariation in great tits (Parus major), using captive-bred full siblings of wild origin. Egg mass, testosterone (T) and androstenedione (A4) hormone concentrations showed moderate heritability, in agreement with earlier findings. Interestingly, yolk triiodothyronine hormone (T3), but not its precursor, thyroxine hormone (T4), concentration was heritable. An immune factor, albumen lysozyme, showed moderate heritability, but yolk immunoglobulins (IgY) did not. The genetic correlation estimates were moderate but statistically non-significant; a trend for a positive genetic correlation was found between A4 and egg mass, T and lysozyme and IgY and lysozyme, respectively. Interestingly, phenotypic correlations were found only between A4 and T, and T4 and T3, respectively. Given that these egg components are associated with fitness-related traits in the offspring (and mother), and that we show that some components are heritable, it opens the possibility that natural selection may shape the rate and direction of phenotypic change via egg composition.母体生殖投入（maternal reproductive investment）可对后代表型（offspring phenotype）产生关键影响，因此这类母体效应（maternal effects）理应受到强烈的自然选择（natural selection）作用。然而，学界对母体效应背后生理机制（physiological mechanisms）的可遗传变异（heritable variation）幅度的认知仍存在局限。在鸟类（birds）中，母体向卵（eggs）内分配资源是影响后代的核心机制，而卵的不同组分未必均可独立调控。我们以野生起源的圈养全同胞（full siblings）家系为研究对象，探究了大山雀（Parus major）卵组分的遗传力（heritability）及其遗传与表型协变关系。研究结果显示，卵重（egg mass）、睾酮（testosterone, T）与雄烯二酮（androstenedione, A4）的激素浓度（hormone concentrations）均表现出中等程度的遗传力，这与此前的研究结论相符。有趣的是，卵黄（yolk）中的三碘甲状腺原氨酸（triiodothyronine, T3）浓度具有遗传力，但其前体（precursor）甲状腺素（thyroxine, T4）的浓度则未表现出遗传力。免疫因子（immune factor）卵清溶菌酶（albumen lysozyme）同样表现出中等遗传力，但卵黄免疫球蛋白（yolk immunoglobulins, IgY）则无此特征。遗传相关（genetic correlation）的估计值处于中等区间，但未达到统计学显著性（statistical significance）；研究分别发现雄烯二酮与卵重、睾酮与溶菌酶、卵黄免疫球蛋白与溶菌酶之间存在正向遗传相关的趋势。有趣的是，仅在雄烯二酮与睾酮、甲状腺素与三碘甲状腺原氨酸之间观察到表型相关（phenotypic correlation）。鉴于这些卵组分与后代（及母体）的适合度相关性状（fitness-related traits）存在关联，且本研究证实部分卵组分具有遗传力，这为自然选择可通过卵组分的变化塑造表型改变的速率与方向提供了可能性。