用生态代谢模型阐释北草蜥个体大小和繁殖投入的地理变异

Metabolic rate, the rate at which organisms take up, transform, and expend energy and materials, is the most fundamental biological rate. Metabolism provides a basis for using first principles of physics, chemistry, and biology to link the biology of individual organisms to the ecology of populations, communities, and ecosystems. The metabolic theory of ecology (MTE) claims that metabolic rate, which is dependent on body size and temperature, affects almost all biological processes and determines life rhythm. The northern grass lizard (Takydromus septentrionalis; Lacertidae) is among reptile species where body size and reproductive output differ among geographically separated populations, but the underlying mechanisms for such a phenomenon have been still far from well known. This project will test two hypotheses within the context of MTE: one is that the population mean adult size should inversely relate to metabolic rate if the elevation of regression lines of mass-corrected metabolic rate against body temperature is higher in populations with smaller sized adults, and the other is that the population mean reproductive output should inversely relate to metabolic rate if the elevation of regression lines of temperature-corrected metabolic rate against body mass is higher in populations with lower reproductive output. We will collect adult lizards of T. septentrionalis from 28 previously sampled localities covering almost the lizard's entire distributional range to gather life-history data on adult size (snout-vent length, SVL), clutch frequency, clutch size, egg size, annual fecundity, annual reproductive output and postpartum female size (mass and SVL), and to determine standard metabolic rates for lizards at body temperatures ranging from 20 C to 34 C. We will use 2 nDNA (RAG1 and PDC) and 2 mtDNA (COI and Cyt b) marks to resolve relationships among intra-specific units, and then use phylogenetic independent contrast to determine associations between local environment and contemporary patterns of geographic variation in body size and reproductive output. This study is the first to use MTE to interpret geographic variation in body size and reproductive output in reptiles, and we hope to find something conceptually new that has never been reported for any other animal taxa.

生态代谢理论（MTE）认为受个体大小和温度影响的代谢率决定几乎所有生物过程和生命节律，基于MTE可探讨各生物组织层次的生态过程和现象，包括个体大小和繁殖输出的地理变异。北草蜥个体大小和繁殖输出地理变异显著，但其潜在的机制尚不清楚。申请人拟从北草蜥分布区内的28个采样点获得材料，收集个体大小、繁殖生活史和20-34 C体温下的标准代谢率等数据，用2个核基因和2个线粒体基因标记重建谱系关系，结合谱系独立性比较，用MTE阐释个体大小和繁殖输出的地理变异，将检验两个假设：（1）若不同种群体重矫正的代谢率与体温的线性回归线高度存在差异，则体形较小的种群应具有较高的回归线高度及相对较高的代谢率；（2）若不同种群体温矫正的代谢率与体重的线性回归线高度存在差异，则繁殖输出较小的种群应具有较高的回归线高度及相对较高的代谢率。本项目是MTE应用于爬行动物的首次尝试，可望获得区别于其它生物类群的创新发现。

采集36个北草蜥样点的样品，选取线粒体基因（Ctyb和COX1）和核基因（RAG1和PDC）作为分子标记，结果显示北草蜥种群可分为东西两大支（具有五个亚支），分歧时间约为1.16百万年前。基于线粒体基因的中性检测和错配分析发现，E1亚支在7.5万年前，E3亚支在2.8万年前和W2在2.2万年前发生扩张，而E3和W2扩张事件刚好和LGM事件相匹配；但是，E2在这个时期（2.5万年前）经历了瓶颈效应。分子结果认为北草蜥片段化的祖先种群，由于喜马拉雅造山运动导致青藏高原抬升所形成特殊的东亚季风气候，以及冰期的气候波动造就了北草蜥现在的分布模式。北草蜥成体体长无性别差异，但雄体头部大小和四肢长显著大于雌体，雌体的腹长显著大于雄体。形态特征种内变异的主要贡献因子为头部大小、四肢长、腹长和体长。其体长和体重的地理变异模式为，随着纬度降低而逐渐减小。四肢长的地理变异模式则为，随着纬度升高而逐渐增加。比较所有种群表型分化值PST和遗传分化值FST发现：所有表型PST显著大于FST，说明种群表型差异受到各自栖息地的环境差异所导致。北草蜥繁殖特征存在窝间差异。首窝卵的窝卵数、窝卵重和相对窝卵重明显高于后续窝卵，而平均卵重无显著窝间差异。首窝卵窝卵数和窝卵重与母体体长呈正相关，窝卵数与卵大小呈负相关。首窝卵或者后续窝卵的窝卵数和窝卵重与气候因子呈正相关关系，而平均卵重则无显著相关性。经谱系独立性分析，我们没有检测到遗传信号。低纬度种群的窝卵数和相对窝卵重大于高纬度种群，而其卵大小显著低于高纬度种群。此种地理差异模式不仅是个体大小差异的结果，主要与热环境地理变异有关，而且卵大小或者平均卵重的地理差异是自然选择的结果，与遗传差异等有关。北草蜥维持能耗存在种群间差异。维持能耗随着温度升高增加，并且非繁殖期的雌雄个体间没有差异。结合维持能耗和繁殖特征，发现北草蜥维持能耗大的种群，其繁殖价低，说明以摄入性繁殖对策的北草蜥在繁殖期，对维持生活活动和繁殖之间存在权衡，高纬度种群倾向于维持能耗高繁殖价低对策。