非生物和生物因子驱动的蛇类趋同进化

Convergence is one of the most important concepts in evolutionary biology, fundamental to studies of biological phenomena in a broad range of disciplines. Convergent evolution describes that two or more unrelated lineages with different ancestral phenotypes independently evolve according to different inclination towards the same adaptive phenotypic characterisitcs. The contrast of intra- and inter-specific variation in morphological, life-history and physiological traits provides original material for interpreting convergent evolution. The last few years have seen an explosion of research into the convergent evolution, with many studies finding that biotic and/or abiotic factors can drive the convergent evolution of phenotypes, these phenotypes may adapt to similar environments in response to common habitats. Ectotherms are of particular interest because most aspects of their morphology and life-history and physiology are strongly influenced by abiotic factors (mainly climatic factors). There has been evidence that sympatric reptiles may display similar adaptive phenotypes via analogous evolutionary responses. This raises the question of whether the convergent evolution is widespread among snakes. To answer this question, we will compare morphological, life-history and physiological traits among three colubrid snakes, Elaphe carinate, Elaphe taeniura and Zaocys dhumnades, collected from five geographically sparated localities where they coexist to identify the traits that show convergent evolution. Traits examined in this study include body size, fecundity (clutch size), egg size, reproductive output, postpartum body condition, the egg size-number trade-off, incubation length (the rate of embryonic development), embryonic stage at oviposition, embryonic metabolic rate, morphology and growth rate of hatchlings and the ability to resist venom produced by the Chinese cobra Naja naja. We will particular attention to how the biotic and/or abiotic factors affect convergent evolution in similar context by comparing intra- and inter-specific variation in the traits examined in the three colubrid snakes. Two hypotheses will be tested in this study: (1) if a trait shows a similar pattern of geographic variation in the three snakes, and this similarity still persists in the common garden experiment, then the convergent evolution of this trait should be detectable in the locality where the three snakes coexist; (2) if venom resistance evolves in the three colubrid snakes as a defense mechansim to fatal attacks from poisonous snakes (Chinese cobras in this case), then nonpoisonous snakes of different species should show the enhanced ability to resist venom in the localities where they sympatric with poisonous snakes. Data generated from this study will aloow us to address questions regarding the convergent evolution of snakes driven by abiotic and biotic factors.

趋同进化是指谱系不同的生物以不同的方式向相似甚至相同的表型独立进化的过程。它是进化生物学领域备受关注的核心研究内容之一。申请人拟以地理上隔离的5个采集地点同域共栖的王锦蛇、黑眉锦蛇和乌梢蛇为研究对象，通过比较形态、生活史特征、卵孵化、新生卵胚胎发育时期、胚胎代谢率和幼体生长速率以及眼镜蛇毒抗性，研究非生物因素（气候因素）和生物因素（同域共栖眼镜蛇）对蛇类表型趋同进化的影响。申请人拟通过本项研究，检验以下两个关于非生物和生物因素可驱使表型趋同的假设：（1）若蛇类形态、生活史特征、胚胎发育和幼体生长速率的地理变异模式均具有共性且在同园实验中仍保持这种共性，则它们在同域分布区应显示被检性状的趋同进化。（2）若无毒蛇在通过提高抗蛇毒性以抵御毒蛇致命攻击方面具有共性，则不同的无毒蛇在与毒蛇同域分布的区域应显示抗蛇毒性的趋同进化。本项目对揭示非生物和生物因素驱使的蛇类趋同进化有重要意义。

通过收集全球158种蛇类（80种卵生和78种卵胎生）母体体长和窝卵数数据进行分析，发现如下主要结果：卵生和卵胎生成年雌蛇平均体长无差异；卵胎生蛇平均相对窝卵重小于卵生蛇类，两种蛇类平均相对窝卵重无显著差异；卵胎生比卵生雌体所产后代数量多且窝卵重更重；卵胎生蛇产出幼体的平均体重与卵生蛇产出卵的平均重量无显著差异；用幼体体重代表后代大小发现，卵胎生蛇后代平均体重大于卵生蛇；卵胎生雌体比相同SVL的卵生雌体平均多产2.8个后代，平均窝卵重多产20 g。从两种蛇类的繁殖特征看，卵胎生蛇类通过产更多更大的后代来弥补产后至越冬时间太短的弊端。. 分析包括游蛇科、眼镜蛇科、细盲蛇科和蝰科在内的34种61个种群蛇类的雌体平均体长、窝卵数或窝仔数、卵重或幼仔重数据发现后代大小-数量权衡显著。考虑谱系关系的影响发现，雌体大小而非谱系关系对后代大小-数量权衡起重要作用。提取物种采集点相关的气候和海拔值进行分析，发现海拔、日温度范围、年降水量、最热季节的平均温度和分配变异占总投入变异的比值存在显著的相关关系。在OLS和PGLS模型中，海拔和日温度范围和投入比呈显著正相关，年降水量和最热月降水量之间存在显著的负相关。. 我们收集6个种群（萧山、天台、九江、江山、全州和舟山）的王锦蛇、乌梢蛇和黑眉锦蛇。乌梢蛇产卵时间最早、黑眉锦蛇次之、王锦蛇最晚；舟山种群的繁殖时间最晚，其次是萧山种群，天台和九江种群次之，江山再次之，最早的是全州种群。在三个物种中，都呈现出从南到北产卵时间以此延迟的现象。三个物种中，体长与尾长和体重存在显著的正相关关系，去除体长影响后，乌梢蛇尾长最长，黑眉锦蛇次之，王锦蛇最短；王锦蛇母体产后体重最大、黑眉锦蛇次之，乌梢蛇最轻。六个种群中，萧山黑眉锦蛇种群体长最短；全州和天台王锦蛇种群体长最短；萧山和全州乌梢蛇种群体长最短。三种蛇类六个种群的繁殖特征显示窝卵数、平均卵重、窝卵重均随母体体长的增长而增多。三个物种六个种群的卵长和卵宽随卵大小的增大而增大。不同种群卵重和卵长的变异呈现在不同物种中呈现出相似的变化趋势，即高纬度（萧山）或气候不稳定（舟山）种群具有更大的变异性，而低纬度或气候较稳定地区的种群变异较小。但不同种群间的卵宽差异不显著，这一点和母体腹腔容纳量有直接关系，动物要使卵大小增大只能通过延长卵长来实现。