蜉蝣亚成虫生态适应特征及进化模式研究

As a group, mayflies are unique in the winged insects because they have two instars with full-developed wings and fly abilities. Morphologically, the subimagos are very similar to their imagos, and both of them can fly well in the air but differences still present between them. As far as known, all male mayflies have subimaginal and imaginal stages in their life history, but some species have lost their female imagos. It seems that the subimaginal stage is necessary to mayflies. However, historically only very limited reports specially discussed and studied the origin, function and morphology of mayfly subimagos. A comprehensive and detailed reseach on this issue has not found yet so far. Here we propose a project on it. In our plan, the life history of one to five species in each family of Chinese Ephemeroptera will be recorded in detail, ecdysis processes of them will be videoed digitally, the exact morphological differences between subimagos and imagos will be scanned and compared. With those information plus higher phylogeny of the order Ephemeroptera, the origin, function, adaptation and evolution of subimagos in the life history will be discussed and analysed. Furthermore, the possible correlations between longevity of subimagos as well as imagos and external morphology (such as body size) or transformation type (molt in water or on land) will be established and reconstructed. If the present proposed research will be adopted, funded and performed as we hope and plan, we believe we can provide much more mayfly specimens of China, valuable information and opinions on classification and evolution of mayflies, and new perspective and ideas on the origin and development of insect metamorphosis as well.

蜉蝣是现存唯一具有两个有翅能飞龄期的昆虫类别，其亚成虫在形态和飞行能力上与成虫既相似又不同。目前已知所有雄性蜉蝣都具亚成虫和成虫阶段，少数种类的雌性只发育至亚成虫，可见此阶段对蜉蝣不可或缺。对蜉蝣亚成虫的起源、作用及与成虫的确切形态区别等只有零星的报道，缺乏较系统的全面研究。本申请拟对我国蜉蝣各科代表性1-5种的生活史进行研究，对它们的羽化过程进行摄像，对亚成虫及成虫形态特征进行全面对比分析，并参考系统发育信息，对它们的进化和生态适应模式进行探讨，以期了解蜉蝣亚成虫在生活史中的作用、蜉蝣保留亚成虫的历史原因和适应意义、不同种类亚成虫期和成虫期存在时间长短与形态（如体型大小）或行为特征（如羽化地点）可能存在的关联性、以及变态过程产生的原因和演化模式。本项研究的实施和完成，将对我国蜉蝣分类和进化提供较为全面丰富的标本和独特见解，对多种昆虫变态类型的起源和演化关系等也能提供新的视角和观点。

蜉蝣的发育过程为原变态，即它们的有翅阶段分为亚成虫期与成虫期，这在昆虫中独一无二。对于亚成虫的起源与作用，历来众说纷纭，大多认为其是原始多个具翅阶段的遗迹，但鲜有实证。. 本项目通过形态对比、生态观察、激素测定和转录组信息分析，认为亚成虫确实是具翅阶段的一个龄期，但却是蜉蝣发育过程中的关键阶段，这在激素变化与基因表达上都有体现。同时，亚成虫身体表面所具有的拒水性微毛等结构确实有利于它们羽化并脱离水的束缚，但亚成虫翅缘缨毛与之无关，它们与后翅缩小呈正相关。从羽化模式来看，蜉蝣末龄稚虫的羽化地点应该是从水外逐渐演化到水面直至水下，这可能也与选择压力有关。也许正是这些因素的共同作用（发育历史、生态作用与自然选择）才使蜉蝣亚成虫得以保留。由于历史的久远和演化过程的多样，蜉蝣原变态发育模式与完全变态、不完全变态相比都不接近，有自己的模式和特点。. 从形态上看，蜉蝣亚成虫保留了许多中间过渡特征，如翅基纵脉愈合模式在少数种类看得更加清楚。我们发现蜉蝣的中脉（M）与肘脉（Cu）在基部是独立的，而它们在蜻蜓中是愈合的，这表明蜉蝣更接近于新翅类。. 在本项目的支持下，我们在全国近20个省市（包括台湾省、香港与澳门）进行了多次标本采集，获得标本4万号以上，并有近500号国外标本。通过对标本的系统分类，我们发现2个新记录科（无爪蜉科Behningiidae与网脉蜉科Euthyplociidae）和10余个新属种。对蜉蝣科Ephemeridae、小蜉科Ephemerellidae、扁蜉科Heptageniidae、四节蜉科Baetidae开展了深入研究。. 项目实施期间，本课题组发表学术论文11篇，其它科普及教学论文4篇，在投稿件5篇，出版专著1部、教材4部。举办与参加国际会议3次，国内学术多次。培养研究生11名，其中博士3名。. 本项目的执行，取得了较明显的成果，培养了多名人才，积累了大量标本。同时在学术上也进一步阐明了蜉蝣原变态、亚成虫存在的意义与演化，可以说圆满完成了任务。