以中国石龙子为模型动物研究蜥蜴母体抚育行为的进化成因

Parental care is defined as any behavioral investment by the parents to increase the fitness of assisted offspring. To explore the pattern and evolutionary causes of parental care is crucial for a better understanding of the core theories of behavior and life history evolution including sexual selection, mother-offspring conflict and reproductive costs. Though being a hot topic in current evolutionary and behavioral ecology and having received considerable scientific attention, the evolutionary cause and adaptive significance of parental care are still far from well known, primarily due to the paucity of comparable data. Some species of lizards display diverse forms of parental care, and are considered as the ideal objects to study the evolution of parental care. In this research project, we will design a series of sophisticated experiments using the Chinese skink, Plestiodon chinensis, as the model animal to identify the proximate causes resulting in maternal care. Specifically, we will observe behaviors associated with maternal care of skinks under different selection pressures (predation risk, ambient temperature, substrate moisture) using night-vision cameras, collect data on egg survivorship, hatchling phenotypes such as morphology, locomotor performance and early growth, and maternal body condition, growth and future reproductive potential, detect the paternity of offspring of the same clutch with some microsatellite loci, collect blood samples of reproductive and nonreproductive females to determine concentrations of three plasma steroid hormones [testosterone (T), 17β-estradio (E2) and cortisol (COR)] by chemiluminescence immunoassay. Moreover, we will summarize data on the role of mating system, life-history and environmental (both biotic and abiotic) factors in influencing female parental care (maternal care) from the scientific literature, and then use a phylogenetic comparative method to identify the ultimate causes for the evolution of maternal care in lizards. Data generated from this study will allow us (1) to evaluate the benefits and costs of maternal care; (2) to examine whether the level of maternal care is related to the pattern of paternity, or to female reproductive investment, or to predation pressure and other ecological (temperature, humidity) factors; (3) to investigate the potential role of steroid hormones in modulating behavior associated with maternal care. The aims of this project are to reveal the evolutionary causes and adaptive significance of maternal care in lizards at both intra- and inter-species levels.

亲代抚育是亲体为提高后代适合度而采取的行为投入。探索亲代抚育的模式及其进化成因，有助于理解性选择、母幼冲突、繁殖代价等行为与生活史进化核心理论，具有重要的学术价值。从亲代抚育缺失到卵胎生，蜥蜴亲代抚育的方式多样，是研究该行为进化的理想材料。本项目以中国石龙子为对象，开展系列因子操纵实验评估不同环境条件下母体抚育所导致的利益与代价，利用微卫星技术检测同窝后代多父本格局，检测类固醇激素（睾酮、雌二醇和皮质醇）在抚育行为中的调控作用，阐明环境捕食压力、基质温湿度、繁殖特征、父权关系等因素对母体抚育投入的影响，揭示蜥蜴母体抚育形成的近因；并应用谱系比较分析方法，阐明蜥蜴亲代抚育的种间进化与其婚配制度、繁殖生活史特征和环境因子等之间的关系，揭示蜥蜴类动物亲代抚育形成的进化远因。从种间及种内两个层面揭示蜥蜴母体抚育行为的进化成因与适应意义。

本项目通过系列操纵实验开展中国石龙子母体抚育行为成因分析的研究。发现（1）抚育母体在抚育期间显著减少巢外活动时间和食物摄入量，抚育结束时状态较差，但后续能相对较快增重，表明抚育行为使母体承受能量代价但能通过补偿性增重使代价较轻；（2）受母体抚育的卵具显著较高的孵化率，孵出幼体表现好，表明抚育行为可给幼体带来明显的存活利益；（3）模拟不同捕食压力下母体产出卵的孵化率较正常抚育组母体略低外，母体在巢址内所待持续时间、母体身体状态以及产出幼体的生长存活情况与正常抚育组无显著差异，表明捕食压力对母体抚育投入和身体状态、以及产出幼体表现的影响并不大；（4）部分窝卵数的改变亦没有影响母体巢址内持续时间、抚育结束后生长情况以及产出幼体表现；（5）处于较暖、基质较湿环境中的母体比较凉、基质较干环境中母体产卵略早，母体抚育有略微提高巢址内温度，缩短卵孵化时间，但一定的温湿度变化对卵孵化率、孵出幼体表现的影响似乎并不大；（6）不同处理组石龙子成体血浆类固醇激素含量、肠道菌群无显著差异。类固醇激素含量、肠道菌群、同窝多父本情况与母体抚育行为的投入表达的关联性可能不大。本研究表明抚育行为产生显著后代利益但较少母体代价可能是母体表达该行为的直接原因，但就目前所获得的数据仍然难以全面地揭示影响母体抚育投入大小的作用因子。