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 nonsignificant; 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.

母体生殖投入可显著影响后代表型，因此这类母体效应（maternal effects）应处于强烈的自然选择压力之下。然而，目前学界对母体效应背后生理机制的可遗传变异程度的认知仍较为有限。在鸟类中，母体向卵内分配资源是影响后代发育的关键机制，而卵的不同组分既可独立调控，也可能无法实现独立调节。本研究以野生来源、经人工繁育的大山雀（Parus major）全同胞家系为实验材料，探究了卵组分的遗传力及其遗传与表型协变关系。研究结果显示，卵重、睾酮（testosterone, T）与雄烯二酮（androstenedione, A4）的激素浓度均表现出中等程度的遗传力，这与此前的研究发现一致。值得注意的是，卵黄三碘甲状腺原氨酸（triiodothyronine, T3）的浓度具有遗传力，但其前体甲状腺素（thyroxine, T4）的浓度则未表现出遗传特征。免疫因子卵清溶菌酶（albumen lysozyme）同样表现出中等遗传力，但卵黄免疫球蛋白（yolk immunoglobulins, IgY）并未呈现显著遗传力。遗传相关估计值处于中等水平，但统计学检验未达显著水平；研究发现A4与卵重、T与溶菌酶、IgY与溶菌酶分别存在正向遗传相关的趋势。有趣的是，仅在A4与T、T4与T3之间检测到了表型相关。鉴于这些卵组分与后代（及母体）的适合度相关性状存在关联，且本研究证实部分卵组分具有可遗传性，这为自然选择可通过卵的组分构成塑造表型变化的速率与方向提供了可能性。