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In many species, newly immigrated or newly dominant males are known to attack and kill dependent infants they have not sired. One of the female counter-strategies against this adaptive male infanticide in group-living taxa is polyandrous mating. A mathematical model demonstrates the existence of a basic conflict of interest between the dominant male and the female. We model the intensity of this conflict, and the pressure to evolve counter-strategies, in relation to (i) the risk of takeover of top dominance by males from inside the group rather than outside and (ii) variation in the relative strength of the dominant male and, thus, expected length of future tenure. The model predicts that dominant males prefer single-male groups, or failing that, prefer multi-male groups with takeovers by outside males. Females, in contrast, generally prefer to live in multi-male groups with takeovers by inside males, but prefer single-male groups if dominant males are extremely powerful. Empirical data suggest that females can control adult group composition, but cannot control either the source of takeovers or relative male strength. The main conclusion is that intersexual conflict in the form of infanticide may over time affect the social system in which a species lives.

Sexually reproducing organisms must process and respond to internal and external stimuli to successfully synchronize physiological and behavioural processes involved in reproduction. One such cue is an individual's social environment. Interactions with conspecifics affect a female's reproductive activity by inducing, suppressing, and/or accelerating reproductive processes. For example, many studies support the theory that the presence of a same-sex conspecific may suppress an animal's reproductive physiology, whereas an opposite-sex conspecific may stimulate an animal's reproductive physiology. The present study determined whether exposure to a conspecific male or female affects the onset of follicular development in sexually-experienced female leopard geckos ( Eublepharis macularius ). The data show that follicular growth was not affected by whether female geckos were housed next to a male conspecific, a female conspecific, or isolated from conspecifics. In addition, the number of days until the initiation of follicular development of female geckos was not affected by whether the females were housed in the presence of a conspecific or in isolation. The results are discussed within the theoretical framework of the effects of social cues on the reproductive physiology of females and the limited empirical data about such effects in squamate lizards.

Chimpanzees live in societies that are characterised both by disorder and order. On the one hand, party size fluctuates in a randomlike fashion and party membership is unpredictable ; on the other hand, fundamental party structures are apparent; males are often in all-male parties whereas females remain mostly solitary. The customary sociobiological explanation is based on the assumptions that 1) competition for food favors solitariness (especially in females); 2) chimpanzee males share the costs of territorial defense against rivals from neighbouring communities and 3) genetical relatedness among males within a community compensates for fitness losses due to their competition for food and females. We point to some theoretical flaws in the reasoning that forms the basis of the current neo-Darwinistic model and to the lack of empirical data concerning male relatedness. Most importantly, chimpanzee-like party structures emerge by self-organisation in an artificial "world" in which "CHIMPs" do nothing more than searching for food and mates, without requiring any of the assumptions of the sociobiological model.