MANETs are self-organizing networks composed of mobile wireless nodes with often scarce resources. Distributed applications based on the P2P paradigm are the best candidates to run over such networks. To profit from the service provided by a P2P overlay (e.g. file sharing), a node needs to be permanently informed about its members (e.g. other peers interested in the same file). This P2P membership management is a costly and difficult task in such dynamic and resource limited environment. We focus on this problem and we propose robust, network-friendly and decentralized algorithms to construct and maintain adaptive topology-aware overlays allowing peer discovery and update. Compared to classical flooding or client-server based approaches, our membership protocol achieves significantly lower network overhead and lower pollution of caches caused by peers who have left. Moreover, and as network split is very frequent in MANETs, our protocol is designed to be partition-aware. It mainly allows separate overlays providing the same service to efficiently merge together when communication opportunities occur. The efficiency of our solution is validated through extensive NS-2 simulations.