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Queen number varies in the population of O. hastatus in SE Brazil. Here, we evaluate how nesting ecology and colony structure are associated in this species, and investigate how reproduction is shared among nestmate queens. Queen number per colony is positively correlated with nesting space (root cluster of epiphytic bromeliads), and larger nest sites host larger ant colonies. Plant samplings revealed that suitable nest sites are limited and that nesting space at ant-occupied bromeliads differs in size and height from the general bromeliad community. Dissections revealed that queens in polygynous colonies are inseminated, have developed ovaries, and produce eggs. Behavioral observations showed that reproduction in polygynous colonies is mediated by queen–queen agonistic interactions that include egg cannibalism. Dominant queens usually produced more eggs. Field observations indicate that colonies can be initiated through haplometrosis. Polygyny in O. hastatus may result either from groups of cofounding queens (pleometrosis) or from adoption of newly mated queens by established colonies (secondary polygyny). Clumping of bromeliads increases nest space and probably adds stability through a strong root system, which may promote microhabitat selection by queens and favor pleometrosis. Rainstorms that frequently knock down bromeliads can be a source of colony break-up and may promote polygyny. Bromeliads are limited nest sites and may represent a risk for young queens leaving a suitable nest, thus favoring secondary polygyny. Although proximate mechanisms mediating queen number are poorly understood, this study suggests that heterogeneous microhabitat conditions probably contribute to the coexistence of variable forms of social structure in O. hastatus.

This study describes two infanticides in a free-ranging group of Callithrix flaviceps. In November 2008, four females gave birth within a period of approximately 10 days. On the day after the third birth, the new mother was attacked by an unidentified individual, resulting in the death of one of her infants due to a bite to the top of the head. Five days later, the fourth female gave birth to twins, and the next day, the more socially dominant of the breeding females was observed ingesting the head of one of these infants. All other infants survived until the end of the study. With the exception of the unusual number of births and attacks, the behaviour appeared typical of that recorded in other marmosets, where socially dominant breeding females attack the offspring of subordinates, apparently as a strategy aimed at reducing competition for the services of infant caregivers.

Societies of ants with several egg-laying queens (polygyny) permit the study of the evolution of a stable allocation of reproduction (reproductive skew). One factor that could influence the stable skew in the polygynous ant Leptothorax acervorum is cannibalism by queens of other queens9 eggs. To test for discrimination during egg-eating, isolated queens were offered a choice between their own eggs and eggs laid by either a nestmate queen or a queen from another colony. The eggs had been made distinguishable by exposing queens to dye. In a total of 45 trials, queens preferentially ate non-nestmate eggs but did not show a significant preference for a nestmate9s over their own eggs. This suggests that mutual egg-eating within colonies does not affect the stable reproductive skew. Once established, indiscriminate egg-eating could be evolutionarily stable because queens that give up egg-eating suffer the costs of having their eggs eaten but lose the nutritional benefits.

Background Monogynous mating systems with extremely low male mating rates have several independent evolutionary origins and are associated with drastic adaptations involving self-sacrifice, one-shot genitalia, genital damage, and termination of spermatogenesis immediately after maturation. The combination of such extreme traits likely restricts evolutionary potential perhaps up to the point of making low male mating rates irreversible and hence may constitute an evolutionary dead end. Here, we explore the case of a reversion to multiple mating from monogynous ancestry in golden orb-web spiders, Nephila senegalensis. Results Male multiple mating is regained by the loss of genital damage and sexual cannibalism but spermatogenesis is terminated with maturation, restricting males to a single loading of their secondary mating organs and a fixed supply of sperm. However, males re-use their mating organs and by experimentally mating males to many females, we show that the sperm supply is divided between copulations without reloading the pedipalps. Conclusion By portioning their precious sperm supply, males achieve an average mating rate of four females which effectively doubles the maximal mating rate of their ancestors. A heritage of one-shot genitalia does not completely restrict the potential to increase mating rates in Nephila although an upper limit is defined by the available sperm load. Future studies should now investigate how males use this potential in the field and identify selection pressures responsible for a reversal from monogynous to polygynous mating strategies.

In social insects, the typical mode of colony foundation occurs when a single queen is inseminated by a male and establishes a new colony, although we can find interspecific and intraspecific variations in queen number and queen-mating frequencies in a single colony. This study aimed to verify the queen number in Pachycondyla striata (Smith) colonies and to evaluate the level of aggressiveness among workers. We collected 14 colonies of P. striata. The behaviors of individuals from five multiple-queen colonies maintained in laboratory were studied by the method of scan sampling. In order to evaluate aggressiveness, dyadic encounters among heterocolonial and homocolonial workers were performed. The results showed that colonies of P. striata can have two or more mated queens (polygynous colonies) besides to monogynous ones (colony containing one queen). Because in polygynous colonies the number of workers was relatively low, such colonies could represent colonies in the foundation phase that characterize a pleometrosis state. In fact, ovarian development analysis from queens showed that the number of queens in the colonies seemed to be unstable. Despite a few cases of oophagy (egg cannibalism), social hierarchy among queens is unclear in comparison to other Pachycondyla species. In addition, aggressiveness increased with distance among nests. Nearby colonies (less than 1 m apart) showed a low level of aggressiveness, suggesting the presence of polydomy, that is, a unique colony can occupy multiple nests. Polygyny associated to polydomy in founding colonies may confer benefits on growth and dispersion of colonies in the studied environments.

This investigation deals with the social structure of multiple-queen colonies of the facultatively polygynous ant Leptothorax acervorum. Five colonies, from Norfolk, U.K., and containing, respectively, 11, 7, 8, 5 and 13 individually marked queens, were observed in laboratory nests for 200 h overall. Thirtyone queens were mated egg-layers, five were mated non-layers, two were virgin layers and six were virgin non-layers. Laying queens had significantly unequal egg productivities within two of the five colonies. Fecundity was positively correlated with queen size, feeding rate and brood handling rate in one colony each, and was unrelated to these in all remaining colonies. There was no association between fecundity and the rates of grooming and receiving grooming in any colony. Queens in all colonies ate eggs and in three colonies the majority of eggs laid were eaten. The majority of cannibalized eggs appearch to be health, reproductive eggs, and queens ate such eggs laid by both other queens and workers. Fecundity and egg-eating rate were positively associated in only one colony. Queens did not defend their eggs, and between-queen aggression and territoriality were almost totally absent. Workers reproduced at a low level in four colonies, but did not eat undamaged eggs. Aggression among workers was relatively common, and there were also three cases of prolonged aggression by workers towards individual queens. These findings suggest that L. acervrum's social system involves reproductive conflicts between queens, between workers and between workers and queens, but the lack of overt aggression apart from egg cannibalism also suggests that such conflicts may take complex, subtle forms.

Policing, i.e. all behaviours that prevent a nestmate from reproducing, is currently observed in social insects. It is presumed to have evolved to regulate potential conflicts generated by genetic asymmetries or to enhance colony efficiency by avoiding surplus reproductives and brood. In the ant, Ectatomma tuberculatum, individual queen fecundity was similar in monogynous and polygynous colonies issued from a Mexican population. Egg cannibalism, however, occurred in the polygynous colonies. The stealing and destruction of reproductive queen-laid eggs involved only nestmate queens, even if they were highly related. No queen appeared to monopolize reproduction in the polygynous colonies. But, the observed value of relatedness among workers differed from the expected value, suggesting an unequal sharing of reproduction between queens. We discussed whether the cannibalism of queen-laid eggs in E. tuberculatum results from a competition for reproduction among queens or if this phenomenon is related to constraints on nutritional resources.

Infanticide has been observed in many different species [1], including common marmosets [2-4], due to sexual selection, reproductive strategies or resource competition [3, 5, 6], which may ultimately lead to exploitation (cannibalism) [1, 7]. Wild callithrichids have a very flexible mating system, including monogamy, polygynandry, polyandry and polygyny [4, 8, 9], with Monteiro da Cruz [10] finding all these patterns within the same population. This results from the high degree of deforestation of their habitat [4], but non-monogamous groups cannot ensure successful rearing of infants, since helpers are crucial and should be present in high numbers [11]. In this study, we show for the first time that cannibalism can follow infanticide, and we hypothesise that it is a result of both competition for scarce resources and the need for animal protein, exacerbated by forest degradation.