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Interactions between individuals of different species are commonplace in animal communities. Some behaviors displayed during these interspecific social interactions may be very similar to those displayed during intraspecific social interactions. However, whether functional analogies between intra- and interspecific behaviors translate at the proximate level into an overlap in their underlying endocrine mechanisms remains largely unknown. Because steroids both mediate social behaviors and respond to them, we approached this question by comparing the behavioral and steroid response of free-living dusky gregories (Stegastes nigricans) to standardized territorial intrusions (sTI) of either conspecific or heterospecific food competitors. Stegastes nigricans is a year-round territorial fish that 'cultivates' the algae on which it feeds and is highly aggressive to both intra- and interspecific intruders. Behavioral differences between intra- and interspecific aggressive responses to sTI were marginal, and sTI tests caused an increase in cortisol levels that was positively related with the levels of aggression. In contrast, androgen levels did not increase in response to sTI, yet they showed a positive relationship with agonistic behavior. These results parallel a pattern that was first described for year-round territorial bird species. Furthermore, they suggest that changes in endocrinehormone levels during territoriality might be independent of the species that induces the territorial response. [ABSTRACT FROM AUTHOR]

Background: In cooperative breeders, subordinates generally help a dominant breeding pair to raise offspring. Parentage studies have shown that in several species subordinates can participate in reproduction. This suggests an important role of direct fitness benefits for cooperation, particularly where groups contain unrelated subordinates. In this situation parentage should influence levels of cooperation. Here we combine parentage analyses and detailed behavioural observations in the field to study whether in the highly social cichlid Neolamprologus pulcher subordinates participate in reproduction and if so, whether and how this affects their cooperative care, controlling for the effect of kinship. Methodology/Principal Findings: We show that: (i) male subordinates gained paternity in 27.8% of all clutches and (ii) if they participated in reproduction, they sired on average 11.8% of young. Subordinate males sharing in reproduction showed more defence against experimentally presented egg predators compared to subordinates not participating in reproduction, and they tended to stay closer to the breeding shelter. No effects of relatedness between subordinates and dominants (to mid-parent, dominant female or dominant male) were detected on parentage and on helping behaviour. Conclusions/Significance: This is the first evidence in a cooperatively breeding fish species that the helping effort of male subordinates may depend on obtained paternity, which stresses the need to consider direct fitness benefits in evolutionary studies of helping behaviour. [ABSTRACT FROM AUTHOR]

1. Ecological conditions and constraints are considered to be important for the evolution of cooperative breeding. However, the importance of the costs of resource acquisition to the decision of subordinates to stay or leave and to help or not have been hardly studied experimentally. Here we reduced the overall food availability (zooplankton) for experimental populations of the cooperatively breeding cichlid fish Neolamprologus pulcher in the field and measured effects on subordinates’ spacing, dispersal, interactions, and helping behaviour. 2. When plankton availability was reduced, all helpers increased feeding rate and moved further away from shelter. Helping correlated negatively with feeding, which suggests a trade-off between foraging effort and cooperation. All group members attacked experimentally presented egg predators later in the food reduction treatment and small helpers in particular decreased their defence effort against them. Furthermore, all subordinates tended to perform less work when food was reduced. 3. This is the first study where food availability was generally reduced in the environment of a cooperative breeder, without affecting the resource distribution between territories. Thereby, our experimental manipulation did not provide dispersal incentives to the test animals, which might have interfered with the decision of subordinates to cooperate. The experimental variation of the costs of resource acquisition for group members revealed significant effects on foraging, spacing, social interactions, and helping behaviour, which highlights the potential importance of ecological constraints on the behaviour, social structure and cooperation propensity in highly social vertebrates. [ABSTRACT FROM AUTHOR]