Variaiton in the composition of small molecule compounds in the egg yolks of Asian Short-toed Larks between early and late broods

The egg yolks of birds contain most of the maternally derived materials required for embryo development and are an important factor influencing embryo development and offspring viability. Individual variation in egg-laying date frequently occurs in passerines inhabiting highly seasonal environments. Females laying in early and late stages of the breeding season encounter different environment temperatures and food conditions, which can affect the levels of metabolities in their bodies, thereby altering the transmission of these materials to the eggs. We test a hypothesis that yolk small molecule compounds of Asian Short-toed Lark (Alaudala cheleensis) could vary between early (mid-May) and late (mid-June) broods. Using the UHPLC-MS/MS method, 683 compounds belonging to 21 compound groups are detected in the yolks. The contents of 18 compounds are significantly different between early and late broods. Ten differential compounds are significantly higher in the early laid eggs, among which γ-aminobutyric acid, creatine, prostaglandins, palmitoleic acid, linoleic acid, and trans linoleic acid are related to low environment temperature response. The eggs laid in late stage exhibit significantly higher levels of 5-L-glutamyl-L-alanine and γ-glutamate-leucine, 1,3-dimethyluric acid and mannose, which may be attributed to females in the late group consuming more insects. We suggest conducting a comprehensive investigation to reveal the yolk small molecule compounds mediated maternal effects on offspring phenotypes under varying ecological conditions.