有鳞类爬行动物卵滞留的生理和分子机制是进化生物学领域重要研究课题之一。早期工作多关注于不同繁殖模式的选择优劣势，但卵滞留期的延长对后代影响以及母体如何实现卵滞留的生理和分子机制尚不清楚。申请人拟以新生卵胚胎时期变异较大（31-36期）的中国石龙子为材料，收集不同滞留期的卵进行孵化并收集表型数据，评价卵滞留对卵生物种的选择利益；收集不同繁殖状态母体输卵管和各发育阶段的胚胎样本，检测不同滞留期内的基因表达差异，寻找母体和胚胎对卵滞留时间双向调控的关键过程和调控方式；收集不同繁殖状态母体血液并测定激素水平，揭示卵滞留过程中激素（生理）调控。本项目聚焦3个关键研究内容：（1）卵滞留时间与幼体适合度之间的利弊权衡关系；（2）母体和胚胎对不同延长卵滞留时间的双向基因调控的分子机制；（3）卵滞留过程中母体的生理调节机制。本项目若能获得资助，将十分有助于解答与爬行动物卵胎生适应进化机制有关的关键科学问题。

Viviparity, a reproductive mode that evolves from oviparity via progressive increases in the length of uterine retention of developing embryos, has had at least 150 independent origins within vertebrates. Viviparity has evolved independently in at least 115 lineages of squamate reptiles (lizards, snakes and amphisbaenians), far more than in all other non-mammalian vertebrates combined. Squamate reptiles therefore provide excellent model systems in which to study the selective forces for the transition from oviparous to viviparous reproduction, and the adaptive significance of this transition. Physiological and molecular mechanisms of egg retention (a necessary intermediate step of the evolutionary transition from oviparous to viviparous reproduction) have long been one of important research topics in evolutionary biology. Earlier studies often use a comparative approach to show selective advanteges or disadvanteges associated with the evolution of reproductive mode from multiple perspectives (e.g., from genes to populations). However, it is still unclear about the potential influence of egg retention on the fitness of both mothers and their offspring and the physiological mechanism and the molecular mechanisms adopted by females to retain eggs. Here, we will use the Chinese skink (Plestiodon chinensis), a unique lizard species with embryonic stages at laying varying over a wider range (from Stage 31-36) than many other oviparous species so far studied, as a model organism to fill this gap. Based on our experimental design, we will collect and incubate eggs with different embryonic stages at laying, and gather data on offspring phenotype to evaluate examine whether the length of egg retention is fitness-related. We will collect oviduct and embryo samples at different developmental stages and then use the transcriptome sequencing technique to identify differentially expressed genes and search for the key processes and modes of bidirectional gene regulation of egg retention between mother and embryo associated with egg retention in oviparous lizards. We will collect blood samples from females at different reproductive states to reveal the hormone levels in the process of egg retention. Scientific questions to be addressed in this study include: 1) the trade-offs between offspring fitness and the length of egg retention; 2) the molecular mechanism for bidirectional (maternal and embryonic) gene regulation of egg retention; and 3) the physiological mechanism of egg retention in P. chinensis. The project, if funded and conducted, will allow us to gather data that will be extremely useful in answering questions raised here and elsewhere about the physiological and molecular mechanisms underlying the evolution of reptilian viviparity.