This paper reports an experimental analysis of conflicting interests in the cooperatively breeding Lamprologus brichardi (Cichlidae). Helpers clearly prefer to stay in the family territory rather than leave for an aggregation of same-size young or for an unoccupied area-even when their chances of reproducing independently are superior to those in the field. Helpers usually attain independence when the breeders force them to leave the territory. Breeders' toleration of helpers depends on the stage in the reproductive cycle, the size of helpers and the need for helpers. Large, previously expelled helpers are reaccepted when competition is increased. In these circumstances breeders prefer their own former helpers to strange young. Experimental and field evidence suggests that 3 factors are ultimately important for the breeder/helper relationship: reproductive parasitism by mature helpers, eventual cannibalism on breeders' eggs and competition for shelter within the territory. A graphical model shows how the initially common interests of breeders and helpers develop divergently when helpers reach the size at which they become sexually mature and less susceptible to predation. Large helpers pay to stay. The relationship of breeders and large helpers meets the criterion of reciprocal altruism.
In brood parasites, knowledge of spacing behaviour, habitat use and territoriality may reveal cues about how parasites find and use their hosts. To study the use of space and habitat of European cuckoos, Cuculus canorus, we radio-tagged 16 females during four consecutive reproductive seasons. We hypothesized that during the laying period cuckoo females should (1) use habitats selectively, and (2) attempt to monopolize potential egg laying areas to reduce competition for host nests. Our data are consistent with the first hypothesis: the use of pond edges compared to forest and transitional habitats was significantly greater than expected from the habitat availability in the total area and within individual female home ranges. All 26 directly observed egg layings and 27 nest visits without laying occurred at pond edges in nests of Acrocephalus spp. Females spent significantly more time at pond edges on egglaying days than on non-laying days. The second hypothesis was not supported: female home ranges overlapped similarly in all three major habitat categories of the potential egg laying areas, and only little aggression was observed between females. We discuss whether female cuckoos may lack territorial behaviour because they are not able to defend egg laying areas economically or because defence is not necessary due to sufficient availability of suitable host nests.
Group size has been shown to positively influence survival of group members in many cooperatively breeding vertebrates, including the Lake Tanganyika cichlid Neolamprologus pulcher, suggesting Allee effects. However, long-term data are scarce to test how these survival differences translate into changes in group extinction risk, group size and composition. We show in a field study of 117 groups from six different colonies (three from two populations each), that group size critically influences these parameters between years. Within one year, 34% of the groups went extinct. Group size correlated positively between years and large groups did not go extinct. The latter were more likely to contain small helpers the subsequent year, which is a cumulative measure of the previous months' reproductive success. Finally, there was a tendency that large groups were more likely to contain a breeding male and female still a year after the first check. The breeder male size, breeder female size, and largest helper size did not influence these parameters, and also did not correlate with the sizes of these categories of fish after one year. This suggests that group size, and not the body size or fighting ability of group members, was the critical variable determining the success of groups. In total, seven groups had fused with other groups between years. To our knowledge, this is the first study showing long-term benefits of large group size in a cooperatively breeding fish. We discuss the importance of differential survival and dispersal of group members for the demonstrated group size effects.
In cooperative breeders, between-group dispersal of helpers is expected to occur if it increases their fitness. Genetic data suggest that helpers in the cooperatively breeding Lake Tanganyika cichlid Neolamprologus pulcher occasionally migrate into nearby groups where they again become helpers. We studied in the field how and why helpers migrate between groups by recording their ranging and social behaviours. We found that helpers spent 5.3% of their time visiting other groups, where they received similar low levels of aggression as within their home group. Large helpers visited other groups more often than small helpers and helpers visited other groups more frequently when the queue in their home group was large, suggesting that helpers with low chances to inherit the territory search for alternatives. Our data show that helpers may use other groups' territories as a refuge, as helpers actively sought shelter within territories of neighbouring groups when we experimentally increased the perceived risk of staying in their home territory. We observed two attempted and one successful case of 'voluntary' (i.e., strategic) between-group dispersal, and experimentally induced three helpers to disperse into other groups. By regular visits, helpers appear to establish familiarity and social relationships with nearby groups, which serve as 'extended safe havens' to hide from predators. In the long run frequent visiting behaviour may facilitate between group dispersal.
The temperate, gonochoristic wrasse Symphodus ocellatus was studied in the field (Corsica). The largest males defend an area within which an average of 3-5 successive nests are built from algae. These brightly coloured, paternal, territorial males (T-males) spend between one and two thirds of their time during the 10-day nest cycle building the nest and fanning. They eat very little at this time, although they consume eggs and invertebrates in the nest, including egg predators. T-males occasionally take over neighbouring nests. Nest acquisition has two functions: nourishment (2/3 of all take-overs) and reproduction (1/3). T-males practising the latter save over 1/3 of the time of a complete nest cycle. Most take-over males that acquire nests solely for nourishment fan it, as do their reproducing counterparts. Small males with inconspicuous female colouration roam about and try to fertilize eggs parasitically when females spawn in T-males' nests. There are usually several of these "sneakers" around successful nests. Medium sized males (smaller than T-males and differently coloured) also cuckold T-males, but often display submissively to them. They participate in nest defence against conspecifics and in interactions with females, with an average effort that even exceeds that of the nest owners. Males displaying this "satellite behaviour" feed much less than sneakers and remain at one nest during most of its spawning phase. They are more tolerated by T-males than are sneakers, although they are on average only half as far away from the nest and thus much more frequently encountered by the T-male. The proportion of time a male spends as a satellite depends on its size. Usually only the largest accessory male at a nest behaves in this manner, though smaller males occasionally perform elements of satellite behaviour. Satellites never participate in nest building, courtship, direct broodcare or interspecific defence, nor do they take over abandoned nests. A fourth type of male, similar in size and appearance to sneakers and satellites, refrains from reproduction in a specific year. These males are perhaps future T-males. All females seem to participate in reproduction every year. They spawn repeatedly in the same nest over one day, but often change nests and T-males on successive days. Male tactics are roughly determined by size, but there are still choices to be made, such as when to give up a nest which has little spawning success, whether to build a nest or to attempt a take-over, or when to reproduce and whether to adopt the sneaker or satellite roles. The simultaneous occurrence of T-males, satellites and sneakers within a species is compared to a few other examples of diverse taxa.
Group size is an important criterion in social decisions. Accordingly, assessing quantities is common in many animals. In fishes, studies on numerical abilities focus on a limited range of species. Arguably, cichlids show the greatest variability of social patterns among vertebrates. Nevertheless, knowledge about their quantitative abilities is scarce. Here we use the Lake Tanganyika cichlid Lamprologus callipterus to scrutinize the quantitative abilities of fish in the context of shoaling. Females chose between different numbers of conspecifics, varying in absolute and relative number differences. In half of the trials both shoals were composed of familiar sisters, while all fish were unfamiliar non-kin in the other half. Test fish consistently preferred the larger of two shoals, irrespective of the ratios. Their activity differed significantly between familiarity/relatedness treatments, indicating recognition of this parameter. L. callipterus therefore has fine-tuned discrimination skills, adding to the evidence that quantitative abilities are widespread in fishes.