Uncovering the molecular mechanisms underlying honest signalling in a lower termite

合作繁殖的脊椎动物和群居昆虫的特点是生殖分工，在这种分工中，繁殖者通常通过化学手段阻碍后代的繁殖。在蚂蚁和白蚁中，角质层碳氢化合物（CHCs）被认为是一种诚实的信号，告诉工蚁蚁后的生育能力。维持诚实信号有两种基本的近似机制。信号可以是制造成本高昂的障碍，也可以是无法伪造的指数，因为它与它所提供信息的财产有因果关系。我们将检验后chcs是一种指数的假设，即后chcs（生育信号）的产生与分子生殖途径（生育）直接相关。在低等白蚁Cryptotermes secundus中，我们最近发现了一个基因（Neofem4），它对蚁后CHCs的产生至关重要。这使得首次揭示群居昆虫生育信号背后的分子途径成为可能。我们假设Neofem4的表达通过保守的分子途径(即胰岛素样信号传导(IIS) -幼体激素（JH) -卵黄蛋白原（Vg）回路）与个体的生育能力直接相关。在内分泌实验和遗传研究的结合中，我们将操纵(a)幼年激素滴度，它作为促性腺激素直接影响生育能力，(b)通过RNA干扰nefem4的表达。通过测试这些操作对种姓成员的行为、化学通讯和基因表达的影响（转录组分析和定量实时PCR），我们将发现(a)生育能力和nefem4表达之间的联系；(b) nefem4下游的途径以及潜在的生育反馈回路。这项研究将诚实信号的指数假设扩展到分子水平，并且第一次有可能测试指数假设。此外，我们的工作将有助于提高我们对社会性昆虫的生殖分工是如何维持的理解，这是社会进化的教科书范例。

Cooperatively breeding vertebrates and social insects are characterized by reproductive division of labour in which reproductives hinder offspring from reproducing often via chemical means. In ants and termites, cuticular hydrocarbons (CHCs) are supposed to function as honest signals that inform the workers about the queens fertility. There are two principle proximate mechanisms for the maintenance of honest signalling. A signal can be a handicap that is costly to produce, or it can be an index that cannot be faked, because it is causally linked to the property it is providing information about. We will test the hypothesis that queen-CHCs are an index, i.e., that the production of queen-CHCs (fertility signalling) is directly linked to molecular reproductive pathways (fertility).In the lower termite Cryptotermes secundus we recently identified a gene (Neofem4) which is essential for production of the queens CHCs. This allows unravelling the molecular pathways underlying fertility signalling in social insects for the first time. We hypothesize that Neofem4 expression is directly linked to the fertility of an individual via conserved molecular pathways (namely, the insulin-like signalling (IIS) - juvenile hormone (JH) - vitellogenin (Vg) circuit). In a combination of endocrine experiments and genetic studies we will manipulate (a) juvenile hormone titres which directly effect fertility as gonadotropic hormones, and (b) Neofem4 expression via RNA interference. By testing the effects of these manipulations on the behaviour, chemical communication and gene expression (transcriptome analyses and quantitative realtime PCR) of caste members we will uncover (a) links between fertility and Neofem4 expression and (b) pathways downstream of Neofem4 as well as potential feedback loops to fertility.This study extends the index-hypothesis of honest signalling to the molecular level and for the first time it will also be possible to test the index-hypothesis. Additionally, our work will contribute to improve our understanding how reproductive division of labour is maintained in social insects, the textbook examples for social evolution.