A wireless sensor network consists of many energyautonomous micro-sensors distributed throughout an area of interest. Each node has a limited energy supply and generates information that needs to be communicated to a sink node. The basic operation in such a network is the systematic gathering and transmission of sensed data to a base station for further processing. During data gathering, sensors have the ability to perform in-network aggregation (fusion) of data packets route to the base station. The lifetime of such a sensor system is the time during which we can gather information from all the sensors to the base station. Given the location of sensors and the base station and the available energy at each sensor, we are interested in finding an efficient manner in which the data should be collected from all the sensors and transmitted to the base station at a given rate, such that system lifetime is maximized. We present an adaptive data aggregation node selection scheme to solve this problem. Our experimental results demonstrate that the proposed protocols significantly outperform previous methods, in terms of energy saving and system lifetime.