Cooperative Brood Care Research Articles

Cooperation, Conflict, and Creching Behavior in Goldeneye Ducks

Crèching behavior, or brood amalgamation, results in offspring being reared by adults other than their genetic parents. Although a variety of hypotheses have been proposed to explain this behavior, most assume either that brood amalgamation is accidental (i.e., nonselected) or that adoption of young is selected for because of social benefits to the young and/or adopting parents. We propose, instead, that brood amalgamation is a function of two separate processes: brood desertion and brood adoption. To examine brood desertion, we develop a graphic model to predict when parents should abandon their young and we test this model experimentally for the Barrow's goldeneye (Bucephala islandica). As predicted, females deserted their offspring when the size of the brood was experimentally reduced. Brood adoption occurred when deserted ducklings joined other broods. However, the success of ducklings in doing so was strongly dependent on the availability of potential host broods and on the age of the recipient broods. Foreign ducklings were readily accepted into young broods (<10 d old) but invariably were rejected from old broods. We could detect no benefits or costs of brood adoption to the host females, contrary to the expectations of a social benefit hypothesis. Our experiments indicate that Crèching behavior is driven by selection on adults to abandon their brood when the benefits of continued investment are outweighed by the reduction in future reproduction and selection on deserted ducklings to join other broods to obtain parental care. Rather than a form of cooperative brood care, Crèching in goldeneyes is perhaps best considered as a form of reproductive parasitism, entailing parent‐offspring conflict over brood desertion and intergenerational conflict over adoption of abandoned young.

Prey Size, Social Competition, and the Development of Reproductive Division of Labor in Social Spider Groups

It has been suggested that the cooperatively social spider, Anelosimus eximius, is eusocial. It has overlapping generations and cooperative brood care, and some females in colonies never reproduce. The hypothesis that the reproductive division of labor arises because of social competition over large prey was tested. Groups of sibling females were provided two types of prey that differed primarily in size. The absolute amount of each type of prey provided fell into three categories. The timing of molt to adulthood and subsequent production of egg sacs was monitored. More spiders molted to adulthood on small fruit flies than on larger houseflies, but the spiders that made it to adulthood in the groups fed larger prey grew larger and produced more egg sacs than the adults on fruit flies at all prey levels. These data suggest that the cooperative capture of large prey in natural colonies influences the formation of a dominant-subordinate dichotomy in which dominants are able to monopolize the resources and se...

Maternal investment of communally nursing female house mice ( Mus musculus domesticus)

Female house mice ( Mus musculus domesticus) belonging to the same polygynous breeding unit rear their litters communally. This paper analyzes the consequences of communal nursing on the number and weight of offspring produced. The reproductive behaviour of monogamous females was compared to that of females living in polygynous groups, consisting of either two familiar sisters or of two genetically unrelated females (unfamiliar until the age of 7 weeks). The lifetime reproductive success of a female was measured as the total number of offspring weaned during a lifespan of 6 months (standardized as 120 days after mating at the age of 8 weeks). The number of litters produced and average litter size per female did not differ significantly between the 3 groups of females. However, females communally nursing with a sister weaned significantly more young than a monogamously paired female. Those sharing a nest with an unrelated female weaned an intermediate number of offspring. Sharing a communal nest with a sister significantly increased the total mass of offspring weaned in comparison with both monogamous females and unrelated females. Furthermore, communal nests improved the birth weight of the young when compared with young in solitary nests. By cooperative brood care and communal nursing, females improved the weight of the young produced. By having a sister for cooperation, a female futher improved the number of offspring weaned when compared with a female rearing litters in solitary nests, as well as the combined weight of offspring weaned compared with all other females studied.

Joint breeding in female burying beetles

Burying beetles (Nicrophorus) exhibit advanced parental care, by feeding and guarding their offspring on buried vertebrate carrion. Till now, interactions between two conspecific females on a carcass have been thought to be mostly competitive, and parental care was thought to be provided by single females or male-female pairs exclusively. Here we demonstrate that cooperative brood care occurs in this species, and that its incidence is contingent on carcass size. Small carcasses are usually monopolized by one female; typically the larger of two female combatants secures the carcass for her offspring (Figs. 1 and 2). On large carcasses fights still occur, but in most cases both females stay on the carcass long enough to provide care for the brood. The use of genetic markers revealed that the maternity of offspring is shared evenly among joint breeders (Figs. 3, 4). We hypothesize that cooperative breeding is an adaptive response to a situation that arises partly as a consequence of a physical constraint.

Origin and evolution of eusociality: a perspective from studying primitively eusocial wasps

Eusocial insects are those that show overlap of generations, cooperative brood care and reproductive caste differentiation. Of these, primitively eusocial insects show no morphological differences between reproductive and worker castes and exhibit considerable flexibility in the social roles that adult females may adopt. This makes them attractive model systems for investigations concerning the origin of eusociality. The rapidly accumulating information on primitively eusocial wasps suggests that haplodiploidy is unlikely to have an important role in the origin of eusociality. General kin selection (without help from haplodiploidy) could however have been an important factor due to the many advantages of group living. Pre-imaginal caste bias leading to variations in fertility is also likely to have some role. Because workers often have some chance of becoming reproductives in future, mutualism and other individual selection models suggest themselves as important factors. A hypothesis for the route to eusociality which focuses on the factors selecting for group living at different stages in social evolution is presented. It is argued that group living originates owing to the benefit of mutualism (the ‘Gambling Stage’) but parental manipulation and subfertility soon become important (the ‘Manipulation Stage’) and finally the highly eusocial state is maintained because genetic asymmetries created by haplodiploidy are exploited by kin recognition (the ‘Recognition Stage’).

Social Behavior in Passalid Beetles (Coleoptera: Passalidae): Cooperative Brood Care

A brief summary is given concerning passalid social behavior in relation to their life cycle. Passalid pairs defend log tunnels and remain with offspring from egg to adulthood. Parent-offspring cooperation involving care of other offspring is a step in the evolution of eusociality. Young adult passalids cooperated with their parents in repair of sibling pupal cases. Cooperative brood care between parents and juveniles has not been reported previously for non-Hymenopterous or non-Isopterous arthropods. The presence of overlap of generations and cooperative brood care by at least temporarily non-reproductive adult individuals in certain passalid species suggest that we might consider these passalids to possess one of the highest levels of subsocial behavior known for arthropods. Habitat, trophic relations between individuals, and sex determination mechanisms suggest parallels with the evolution of termite sociality.

The Evolution of Eusociality

Eusociality is characterized by overlapping adult generations, cooperative brood care, and more or less nonreproductive workers or helpers (96, 151). Evolutionists have long recognized that the presence of sterile workers is difficult to explain by traditional individual selection (128). Darwin said of the workers in eusocial insects that they posed special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory . . . [because] being sterile, they cannot propagate their kind (44, p. 236). Darwin proposed that workers evolve through selection at the level of the colony, a mechanism that is probably important in several respects (39, 109). Processes at the colony level, however, do not fully explain why individuals give up reproduction and hence the possibility of passing on their genes via offspring. Williams & Williams (149) and Hamilton (63, 65) showed that genetic related­ ness between the workers and the reproductives they help raise may resolve the apparent paradox. The most extreme cases of eusociality are species with highly specialized, permanently sterile castes of workers and soldiers. Sterile castes have evolved in the Hymenoptera (ants, bees, and wasps), Isoptera (termites), and apparently in one rodent (the naked mole-rat). Eusociality has arisen many times indepen­ dently in Hymenoptera (albeit not always to the point of permanent worker sterility), and most of the discussion of the evolution of eusociality has focused on that order. This review begins with an evaluation of the various hypotheses proposed to explain the evolution of eusociality in Hymenoptera and Isoptera. A compara­ tive analysis of preconditions that are important for the evolution of insect