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.