نظریه قرارداد برای تکامل همکاری: مشوق های مناسب جذب شرکای درست

Partner choice is a critical stage of many biological interactions, from mating to cooperation. When the quality of the potential partners is unknown, one way to choose is to rely on signaling: costly signals can reveal the quality of the sender and allow the receiver to choose. In some cases, however, signaling (or an active choice based on signals) is not possible, for example in the initiation of the symbiosis between the squid Euprymna scolopes and the bioluminescent bacterium Vibrio fischeri. How is partner choice possible in this and other similar cases? I show that in a game with asymmetric information without signaling, imposing a deliberate cost for establishing the interaction allows the non-informed individual to attract the right partner if the cost induces only high quality individuals to accept the interaction. Furthermore, imposing different costs and rewards may induce the informed individuals to screen themselves according to their types, and therefore allow the non-informed individual to establish an association with the correct partners in the absence of signaling.

How to choose among potential partners when their quality is unknown? In many pairwise interactions one party has relevant information (for example about his own quality) that the other party does not have. Consider mate choice: in many species females choose males (Andersson, 1995), but they cannot observe their quality directly. While females prefer males of good quality, males would find it profitable to mate irrespective of their quality, therefore they have an incentive to reveal their real quality only if they are good, and to pretend they are good if they are not. How can a female tell a good quality male from a bad quality one? The problem of partner choice (Bull and Rice, 1991, Noë and Hammerstein, 1994 and Sachs et al., 2004) is not restricted to sexual selection; it is relevant in any situation in which information is asymmetric.

Imposing a strategic cost for an establishing and maintaining an interaction can allow an individual to find the right partner among individuals of unknown quality by inducing them to screen themselves according to their type. Like in signaling theory, a strategic cost allows the screening; in this case however, the informed individual does not need to signal and the non-informed individual does not need to choose. This can help explain cases of partner choice in the absence of signaling, like the symbiosis between squids and bioluminescent bacteria. Other species of fish, mollusks, insects, worms and cnidarians that support cooperative bacterial associations produce ROS (Ruby and McFall-Ngai, 1999) and are therefore good candidates for a similar screening mechanism. Plants that must establish an association with mutualistic ants face the same problem of asymmetric information faced by a squid that must interact with bioluminescent bacteria, and a similar screening mechanism may be operating in these cases (Yu and Davidson, 1997). These and other examples are discussed at length elsewhere (Archetti et al. forthcoming).