Brood pheromone modulates honeybee (Apis mellifera L.) sucrose response thresholds

Foraging behavior and the mechanisms that regulate foraging activity are important components of social organization. Here we test the hypothesis that brood pheromone modulates the sucrose response threshold of bees. Recently the honeybee proboscis extension response to sucrose has been identified as a ”window” into a bee’s perception of sugar. The sucrose response threshold measured in the first week of adult life, prior to foraging age, predicts forage choice. Bees with low response thresholds are more likely to be pollen foragers and bees with high response thresholds are more likely to forage for nectar. There is an associated genetic component to sucrose response thresholds and forage choice such that bees selected to hoard high quantities of pollen have low response thresholds and bees selected to hoard low quantities of pollen have higher response thresholds. The number of larvae in colonies affects the number of bees foraging for pollen. Hexane-extractable compounds from the surface of larvae (brood pheromone) significantly increase the number of pollen foragers. We tested the hypothesis that brood pheromone decreases the sucrose response threshold of bees, to suggest a pheromone- modulated sensory-physiological mechanism for regulating foraging division of labor. Brood pheromone significantly decreased response thresholds as measured in the proboscis extension response assay, a response associated with pollen foraging. A synthetic blend of honeybee brood pheromone stimulated and released pollen foraging in foraging bioassays. Synthetic brood pheromone had dose-dependent effects on the modulation of sucrose response thresholds. We discuss how brood pheromone may act as a releaser of pollen foraging in older bees and a primer pheromone on the development of response thresholds and foraging ontogeny of young bees. Received: 24 May 2000 / Revised: 26 September 2000 / Accepted: 15 October 2000     

Evolution of extreme polyandry in the honeybee Apis mellifera L.

A number of hypotheses have been proposed to explain the evolution of multiple mating in the honeybee queen. In particular, the consequences of reduced intracolonial relatedness provide plausible explanations for multiple mating with up to ten drones, but fail to account for the much higher mating frequencies observed in nature. In this paper, we propose an alternative mechanism which builds on non-linear relationships between intracolonial frequencies in genotypic worker specialization and colony fitness. If genes for any worker specialization confer an advantage on colony fitness only when they are rare, this would require a stable mix of sperm from a few drones which contribute that trait, and many which do not. To ensure both specific, low within-colony proportions of “rare specialist” genes, and to reduce random variation of these proportions would require mating with high numbers of drones. The quantitative implementation shows that moderate to very high numbers of matings are required to exploit colony advantages from genotypic allocation of workers to rare tasks. Extreme polyandry thus could result from colony selection dependent on the intracolonial frequency of rare genetic specialists. Received: 30 January 1998 / Accepted after revision: 7 October 1998     

The causes of the tremble dance of the honeybee,Apis mellifera

Tremble dances are sometimes performed by returning forager bees instead of waggle dances. Recent studies by Seeley (1992) and Kirchner (1993) have revealed that this behaviour is part of the recruitment communication system of bees. The ultimate cause of tremble dances is, according to Seeley (1992), an imbalance between the nectar intake rate and the nectar processing capacity of the colony. This imbalance is correlated with a long initial search time of returning foragers to find bees to unload them. However, it remained unclear whether a long search time is the direct proximate cause of tremble dancing. Here we report that a variety of experimental conditions can elicit tremble dances. All of them have in common that the total search time that foragers spend searching for unloaders, until they are fully unloaded, is prolonged. This finding supports and extends the hypothesis that a long search time is the proximate cause of tremble dancing. The results also confirm the previous reports of Lindauer (1948) and others about factors eliciting tremble dancing.     

Evolution of worker sterility in honey-bees (Apis mellifera): how anarchistic workers evade policing by laying eggs that have low removal rates

In anarchistic honey-bee colonies, many workers’ sons are reared despite the presence of the queen. Worker-laid eggs are normally eaten by other workers in queenright colonies. Workers are thought to discriminate between queen-laid and worker-laid eggs by the presence or absence of a queen-produced egg-marking pheromone. This study compared the survival of three classes of eggs (worker-laid eggs from anarchistic colonies, worker-laid eggs from non-anarchistic queenless colonies, and queen-laid eggs) in both queenright normal colonies and queenright anarchistic colonies, in order to test the hypothesis that anarchistic workers evade policing by laying more acceptable eggs. As expected, few worker-laid eggs from non-anarchistic colonies survived more than 2 h. In contrast, worker-laid eggs from anarchistic colonies had much greater acceptability, which in some trials equalled the acceptability of queen-laid eggs. Anarchistic colonies were generally less discriminatory than normal queenright colonies towards worker-laid eggs, whether these originated from anarchistic colonies or normal queenless colonies. This indicates that the egg-removal aspect of the anarchistic syndrome involves both worker laying of eggs with greater acceptability and reduced discriminatory behaviour of policing workers. Received: 19 July 1999 / Received in revised form: 3 November 1999 / Accepted: 20 November 1999     

The modulation of worker behavior by the vibration signal during house hunting in swarms of the honeybee, Apis mellifera

During house hunting, honeybee, Apis melli- fera, workers perform the vibration signal, which may function in a modulatory manner to influence several aspects of nestsite selection and colony movement. We examined the role of the vibration signal in the house-hunting process of seven honeybee swarms. The signal was performed by a small proportion of the older bees, and 20% of the vibrating bees also performed waggle dances for nestsites. Compared to non-vibrating controls, vibrating bees exhibited increased rates of locomotion, were more likely to move into the interiors of the swarms, and were more likely to fly from the clusters and perform waggle dances. Recipients responded to the signal with increased locomotion and were more likely than non- vibrated controls to fly from the swarms. Because vibration signals were intermixed with waggle dances by some vibrators, and because they stimulated flight in recipients, the signals may have enhanced nestsite scouting and recruitment early in the house-hunting process. All swarms exhibited increased vibration activity within 0.5–1 h of departure. During these final periods, numerous vibrating bees wove repeatedly in and out of the clusters while signaling and motion on the swarms increased until it culminated in mass flight. The peaks of vibration activity observed at the end of the house-hunting process may therefore have activated the entire swarm for liftoff once a new nestsite had been selected. Thus, the vibration signal may help to integrate the behavior of numerous groups of workers during nestsite selection and colony relocation. Received: 17 January 2000 / Received in revised form: 5 April 2000 / Accepted: 3 May 2000     

Vibrational signals in the tremble dance of the honeybee,Apis mellifera

Summary The tremble dance is a behavior sometimes performed by honeybee foragers returning to the hive. The biological significance of this behavior was unclear until Seeley (1992) demonstrated that tremble dances occur mainly when a colony's nectar influx is so high that the foragers must undertake lenghty searches in order to find food storers to unload their nectar. He suggested that tremble dancing has the effect of stimulating additional bees to function as food-storers, thereby raising the colony's capacity for processing nectar. Here I describe vibrational signals emitted by the tremble dancers. Simulation experiments with artificial tremble dance sounds revealed that these sounds inhibited dancing and reduced recruitment to feeding sites. The results suggest that the tremble dance is a negative feedback system counterbalancing the positive feedback of recruitment by waggle dances. Thus, the tremble dance seems to affect not only the colony's nectar processing rate, but also its nectar intake rate.     

Differential feeding of worker larvae affects caste characters in the Cape honeybee,<Emphasis Type="Italic"> Apis mellifera capensis</Emphasis>

Sections of brood from colonies of the Cape honeybee ( Apis mellifera capensis), the African honeybee ( A. m. scutellata), and hybrid bees of the two races were exchanged between colonies to study the effect of different brood-origin/nurse-bee combinations on development of caste characters. When Cape larvae were raised by African workers the amount of food provided almost doubled in comparison with Cape larvae reared by their own workers. In contrast, African larvae raised by Cape workers were provided with only half the amount they received from their own workers. After the bees emerged, we found a large degree of plasticity in characters related to caste differentiation, which corresponded closely to the amount of food provided. Super-fed Cape bees had enlarged spermathecae, were heavier than normal workers and developed more rapidly, and had reduced pollen combs, all typical for a more queen-like condition. Ovariole numbers did not appear to be enhanced by additional feeding. Cape bees that behave as social parasites in African bee colonies were most queen-like in the characters studied, albeit within the range that was found for Cape bees from normal colonies, suggesting within-colony selection for characters that enhance reproduction.Communicated by R. Page     

Lack of kin recognition in swarming honeybees ( Apis mellifera )

Honeybee colonies reproduce by colony fission and swarming. The primary swarm leaves the nest with the mated mother queen. Further “after-swarms” can leave the nest. These are composed of virgin queens and sister workers. Since all workers in the primary swarm have the same relationship to the mother queen, kin recognition cannot have any effect on the worker distribution in the swarm. Because of polyandry of the mother queen, the after-swarm is composed of super- and halfsister workers of the virgin queen. In this case kin recognition might affect swarm composition if workers increase their inclusive fitness by preferentially investing in a supersister queen. The distribution of workers in the mother colony, the primary and the after-swarm was analyzed using single-locus DNA fingerprinting in two colonies of the honeybee (Apis mellifera). The colonies were composed of 21 and 24 worker subfamilies because of multiple mating of the queen. The subfamily distribution in the mother colonies before swarming was significantly different from the subfamily frequencies in the primary swarm. This indicates different propensities for swarming in the various subfamilies. The subfamily distribution was also significantly different between the mother colony and the after-swarm. There was however no significant difference between the subfamily composition of the primary and the after-swarm. The average effects of kin recognition on the distribution of the subfamilies in the two after-swarms were less than 2%. We conclude that colony-level selection sets the evolutionary framework for swarming behaviour. Received: 22 May 1996 / Accepted after revision: 2 November 1996     

Reproductive conflict in honey bees: a stalemate of worker egg-laying and policing

 Using electrophoretic markers, eggs laid by workers were identified in honey bee (Apis mellifera) colonies with a queen. Based on extrapolation, these represented about 7% of the unfertilized (male) eggs laid in the colonies. A very small proportion of workers (of the order of 0.01%) lay these eggs. Worker-laid eggs are rapidly removed, so that very few sons of workers are reared. Thus the reproductive cooperation in bee colonies is maintained by ongoing antagonistic interactions among the members of the colony, with worker laying and egg removal policing by other workers being relatively common. Received: 24 November 1995/Accepted after revision: 25 May 1996     

Colony-level selection effects on individual and colony foraging task performance in honeybees, Apis mellifera L.

In honeybees, as in other highly eusocial species, tasks are performed by individual workers, but selection for worker task phenotypes occurs at the colony level. We investigated the effect of colony-level selection for pollen storage levels on the foraging behavior of individual honeybee foragers to determine (1) the relationship between genotype and phenotypic expression of foraging traits at the individual level and (2) how genetically based variation in worker task phenotype is integrated into colony task organization. We placed workers from lines selected at the colony level for high or low pollen stores together with hybrid workers into a common hive environment with controlled access to resources. Workers from the selected lines showed reciprocal variation in pollen and nectar collection. High-pollen-line foragers collected pollen preferentially, and low- pollen-line workers collected nectar, indicating that the two tasks covary genetically. Hybrid workers were not intermediate in phenotype, but instead showed directional dominance for nectar collection. We monitored the responses of workers from the selected strains to changes in internal (colony) and external (resource) stimulus levels for pollen foraging to measure the interaction between genotypic variation in foraging behavior and stimulus environment. Under low-stimulus conditions, the foraging group was over-represented by high-pollen-line workers. However, the evenness in distribution of the focal genetic groups increased as foraging stimuli increased. These data are consistent with a model where task choice is a consequence of genetically based response thresholds, and where genotypic diversity allows colony flexibility by providing a range of stimulus thresholds. Received: 3 May 1999 / Received in revised form: 22 December 1999 / Accepted: 23 January 2000     

Molecular genetic and behavioral analysis of social organization in the Asian elephant (Elephas maximus)

We report on the genetic evaluation and behavioral study of social organization in the Asian elephant (Elephas maximus). Although Asian elephants and African elephants (Loxodonta africana) were previously thought to have similar social organizations, our results demonstrate a substantial difference in the complexity and structure of Asian elephant social groupings from that described for African savanna elephants. Photographic cataloging of individuals, radio telemetry, and behavioral observations in Ruhuna National Park, Sri Lanka, enabled us to assign associated females and young to four groups with overlapping ranges. Genetic sampling of individuals from the four groups in Ruhuna National Park and three other groups in surrounding areas, conducted through PCR amplification and sequencing of mitochondrial DNA from dung, supported the matriarchal nature of female groups and the lack of inter-group transfer of females. Behaviorally and genetically, the identified social groups were best described as ”family groups”. We did not find any evidence for the existence of social groups of higher complexity than family groups. Received: 25 March 2000 / Received in revised form: 28 March 2000 / Accepted: 1 April 2000     

Cuticular volatiles,attractivity of worker larvae and invasion of brood cells by Varroa mites. A comparison of Africanized and European honey bees

Summary. Africanized honey bees (AHBs) of Brazil and Mexico have proven to be tolerant to Varroa destructor mites. In contrast, European honey bees (EHBs: Apis mellifera carnica) at the same tropical study site are highly intolerant to these ectoparasites. A lower attractiveness of Varroa-tolerant AHB larvae has been hypothesised to be an important trait in reducing the susceptibitlity of AHBs to these mites. Thus, selection for EHB brood that is less attractive to mites is thought to be one possibility for limiting mite population growth and thus increase the tolerance of EHBs to the mite.?In Ribeir?o Preto, Brazil, European A. m. carnica bees and AHBs were tested with respect to their rate of brood infestation and brood attractiveness to Varroa mites. For the comparison of brood infestation rates, we introduced combs with pieces of EHB and AHB brood into honey bee colonies (18 repetitions). The relative infestation rate of EHB brood was significantly higher compared to AHB brood.?The preference behaviour of single Varroa mites was tested in a laboratory bioassay where either living host stages were offered or host extracts were presented on dummies. By these tests we could confirm the preference of Varroa females for certain developmental host stages and for their corresponding extracts. In contrast to the within-colony results, Varroa mites in the laboratory bioassay showed a slight preference for AHB compared to EHB larvae.?The gas chromatographic analysis revealed differences in the chemical spectrum of extracts obtained from different larvae. In accord with the results of the bioassays, we could detect stage-specific odour differences in larval cuticular compounds, including methyl esters and hydrocarbons that have been described as kairomones. None of these substances, however, revealed significant race-specific differences. Therefore, the quantity and composition of certain cuticular compounds seem to be responsible only for the recognition of a suitable host stage by Varroa females. The different infestation rates in the colonies, however, seem to be caused neither by race-specific differences in attractiveness of bee larvae nor by an extended attractive period of EHB larvae: both AHB and EHB larvae become attractive approximately 21 h before capping of the brood cell, and thus have the same window of time when they can be parasitised.?Therefore differential Varroa-infestation rates are not related to larval attraction but probably are determined by other race-specific and colony-related factors. Received 11 June 2001; accepted 19 November 2001.     

The effect of queen-worker conflict on caste determination in the bumblebee Bombus terrestris

Endocrine analyses were used to investigate the well-known association between queen production and the onset of worker reproduction (termed the competition phase, CPh) in Bombus terrestris. Larvae that reached the age of 5 days before the CPh had a worker-like profile: low juvenile hormone (JH) biosynthesis rates and low JH hemolymph titers. In contrast, larvae that reached the age of 5 days during the CPh had a queen-like profile: high JH biosynthesis rates and high hemolymph JH levels. Larval fate could be manipulated by transplanting egg cells into host colonies with different social structures. There was a steep rise in JH production in larvae transplanted into colonies near or during the CPh. This indicates that during colony development, larvae switch from the ”worker developmental pathway” to the ”queen developmental pathway,” and that the switch is socially regulated. In small rearing groups, larvae reared with queens before the CPh developed into workers, whereas those reared with queens after the CPh developed into queens. Variation in worker type (naive or experienced) did not affect caste determination. Therefore, we hypothesize that queens produce a pheromone that directly inhibits queen differentiation by larvae. We also present two alternative scenarios that explain the timing of gyne production in B. terrestris, one based on ecological constraints and the other based on queen-worker competition. Received: 20 October 1999 / Received in revised form: 18 December 1999 / Accepted: 23 January 2000     

Quantitative variation in ecological and hormonal variables correlates with spatial organization of pronghorn (Antilocapra americana) males

Whereas variation in pronghorn (Antilocapra americana) spatial organization is well documented, underlying ecological or physiological explanations are not well understood. This study quantitatively describes spacing systems of pronghorn males and correlates of their spatial organization. I collected behavioral data from two populations in South Dakota (Wind Cave) and Montana (Bar Diamond) to determine if males differed in space use, response to intruders, and behavior patterns indicative of area defense. I measured sex ratio and population density, and I examined characteristics of food resources, including forb species diversity, richness, coverage, biomass, and nitrogen content, and how they changed during the growing season. I also collected and analyzed fecal samples to determine if males differed in testosterone concentrations. Pronghorn males at Wind Cave were more territorial than males at Bar Diamond, although males at Bar Diamond became more territorial during the second year. The forb community at Wind Cave was more diverse, contained greater amounts of forbs later in summer, and had a higher nitrogen content later in summer. Population density was lower at Wind Cave, although density dropped at Bar Diamond during the second year, and sex ratios were skewed toward males at Bar Diamond. Finally, males at Wind Cave had higher testosterone concentrations than did Bar Diamond males, although differences were not statistically significant. With lower population density and higher forb abundance and quality, food resources were more economically defensible at Wind Cave, and males were more territorial there. Analyses using these and other pronghorn populations revealed that population density and sex ratio correlated weakly with spatial organization, whereas precipitation correlated most strongly, which suggests plant productivity has a powerful role in determining pronghorn territoriality. Received: 16 June 1999 / Received in revised form: 21 September 1999 / Accepted: 31 December 1999     

The influence of potential reproductive rate and variation in mate quality on male and female choosiness in the sand goby, Pomatoschistus minutus

Recent models of choosiness in mate choice have identified two particularly important factors: the potential reproductive rate (PRR) of the choosing sex relative to that of the chosen sex, and the variation in quality of potential mates. This experimental study tested how these factors affected choosiness in male and female sand gobies, Pomatoschistus minutus. We manipulated relative PRR by means of water temperature, and mate quality by means of body length. The choosing male or female was offered a choice between two mates with either a small or a large difference in body length representing a small or a large variation in mate quality. Choosiness was measured as (1) preference for the larger mate, and (2) as whether or not spawning occurred with the smaller mate, while the larger mate was visible but screened off. We found that females preferred large males, and that their level of choosiness was affected by variation in male quality, but not by their own relative PRR. Males, on the other hand, seemed unselective in all treatments and were in general more likely than females to spawn with their provided partner. This suggests that in the sand goby, variation in male mate quality has a greater influence than relative PRR on facultative changes in female choosiness. However, a general difference in PRR between males and females may be one important factor explaining the observed sex difference in choosiness. Received: 17 April 2000 / Revised: 24 June 2000 / Accepted: 17 July 2000     

Mate choice games, context-dependent good genes, and genetic cycles in the side-blotched lizard, Uta stansburiana

According to mate choice models, a female should prefer males with traits that are reliable indicators of genetic quality which the sire can pass on to their progeny. However, good genes may depend on the social environment, and female choice for good genes should be context dependent. The side-blotched lizard, Uta stansburiana, exhibits genetically based throat colors (orange, blue, or yellow) that could be used as a sexually selected signal since they reliably predict the genetic quality of mates. The frequencies of male and female morphs cycle between years, and both male and female morphs have an advantage when rare; thus genetic quality will depend on morph frequency. A female should choose a sire that maximizes the reproductive success of both male and female progeny. We examine a game theoretical model that predicts female mate choice as a function of morph frequency and population density. The model predicts the following flexible mate choice rule: both female morphs should prefer rare males in ’boom years’ of the female cycle (e.g., ’rarest-of-N rule’), but prefer orange males in ’crash years’ of the female cycle (’orange-male rule’). Cues from the current social environment should be used by females to choose a mate that maximizes the future reproductive success of progeny, given the social environment of the next generation. We predict that the cue is the density of aggressive orange females. In the side-blotched lizard, cycling mate choice games and context-dependent mate choice are predicted to maintain genetic variation in the presence of choice for good genes. Received: 8 March 2000 / Revised: 26 August 2000 / Accepted: 4 September 2000     

Environmental and genetic determinants of the male forceps length dimorphism in the European earwig Forficula auricularia L.

Male dimorphisms are particularly conspicuous examples of alternative reproductive strategies. The male forceps length dimorphism in the European earwig Forficula auricularia has long been considered an example of a status- (body size) dependent male dimorphism. In this paper, I test three hypotheses relating to the dimorphism of F. auricularia. First, that the dimorphism is status dependent and determined by nutrition. Second, that the dimorphism is a density-dependent adaptation. Third, that there is a genetic basis to population differences in morph frequency seen in the field. These hypotheses were tested by rearing two populations in a split-family rearing design with two diets and two densities. Populations of male earwigs reared in the common garden differed in forceps length and relative forceps length. The populations also differed in the morph frequencies, with 40 versus 26% long-forceped males. These results confirm the notion that there is a genotype-by-environment interaction that determines the morph frequency in a population. There were only minor effects of density on male forceps length and no influence of density on the male dimorphism. In accordance with the hypothesis that the morphs are status-dependent alternatives, large-forceped males only arose on the high-protein diet that produced earwigs of a large body size. However, not all large males produced the long-forceped phenotype. I put forward an extension of the status-dependent dimorphism model that may account for the pattern of forceps dimorphism in this species. Received: 18 November 1998 / Received in revised form: 14 May 1999 / Accepted: 25 July 1999     

Variation among populations of the sailfin molly in the rate of concurrent multiple paternity and its implications for mating-system evolution

We examined patterns of concurrent multiple mating in a live-bearing poeciliid fish, the sailfin molly (Poecilia latipinna). We tested whether the probability of multiple paternity was related to female body size or fertility and whether the rate of multiple paternity varied among four populations that differed in their distributions of female body size and fertility. We analyzed data on mother and offspring genotypes for three polymorphic allozymes by three techniques, including a maximum-likelihood estimator that accounts for sampling error in both parental and offspring allele frequencies. The estimated rate of multiple paternity varied between 0.09 and 0.85, and the rate in one population varied seasonally between 0.33 (spring) and 0.85 (autumn). The variation in these rates was not associated with variation in body-size distributions among populations but was closely associated with variation in size-specific fertility: populations with greater variation in female fertility had higher multiple-paternity rates. Within two populations, logistic regression revealed that individual females of larger body size and greater size-specific fertility were more likely to carry multiply sired broods. This result is consistent with observations made in one of the populations 5 years earlier. In general, the results strongly suggest that the mating system varies markedly among conspecific populations of sailfin mollies and that larger, more fertile females are the objects of intermale competition. Received: 6 May 1996 / Accepted in revised form: 5 December 1996     

Interdemic variation in mixed-species association patterns: common diurnal primates of Kibale National Park, Uganda

We used interdemic variation in the tendency to form mixed-species groups to examine the costs and benefits of association among the primates of Kibale National Park, Uganda. A year-long survey of six sites revealed that the amount of time that the five common diurnal primates [red colobus (Procolobus tephrosceles), black-and-white colobus (Colobus guereza), redtail monkeys (Cercopithecus ascanius), blue monkeys (Cercopithecus mitis), and grey-cheeked mangabeys (Lophocebus albigena)] spent in mixed-species groups varied dramatically among sites. In many cases, the proportion of time that species associated was positively related to their densities. By using detailed behavioral observations of redtail monkeys and red colobus made over 4 years (2660 h) at four sites, we were able to reject the null hypothesis that associations occur by chance for only one of four sites. However, a correlative approach exploring the costs and benefits of association suggests that ecological variables do influence association patterns. We found that redtail monkeys and red colobus overlapped in diet (19.2% of their foraging effort) and traveled further when in mixed-species groups than when alone. Having demonstrated this, we examined the applicability of the ecological constraints model for predicting the proportion of the time spent in mixed-species groups based on food availability. For this analysis we concentrated on red colobus from the site with 35 months of observation and demonstrated that their tendency to be in mixed- species groups was related to food availability. We used two methods to examine if mixed-species associations function to decrease predation risk. First, chimpanzees are known to prey heavily on red colobus, but rarely kill other primates. The time red colobus spent in mixed-species groups was correlated to chimpanzee density, but it was not for the other monkey species, suggesting that mixed-species groups serve to decrease predation risk. Second, when red colobus groups contain more infants and are presumably at the greatest risk of predation, they form mixed-species groups most often. These results demonstrate that the costs and benefits of mixed-species associations vary dramatically over small spatial and temporal scales. If such variation is generally the case, then studies conducted at different locations or different times could easily highlight the importance of difference selective agents in favoring mixed-species associations. Received: 10 February 1999 / Received in revised form: 16 September 1999 / Accepted: 2 October 1999     

Genetic evidence for mixed parentage in nests of the emu (Dromaius novaehollandiae)

Parentage in emus (Dromaius novaehollandiae) was examined by microsatellite analysis using four independent loci. Of 106 chicks sampled in one breeding season from 18 nests, 54 (51%) were not fathered by the nesting male, 12 (11%) were not from the observed mate of the sitting male, and 9 (8%) represented intra-specific brood parasitism, having no alleles in common with either nest parent. Some males (11%) fathered all chicks in their nests, but the majority showed high levels of cuckoldry. Those males commencing incubation earliest in the season tended to have the highest levels of paternity in their own nests. These results reveal a high frequency of extra-pair fertilisations and resultant cuckoldry in a predominantly socially monogamous bird and support recent reports which have described the emu mating system as a complexity of polyandrous, promiscuous and monogamous behaviour. Parentage assignment of chicks resulting from extra-pair fertilisations revealed an evenly scattered pattern of paternity that did not show any particular male dominance in reproductive success. These results lead to a reassessment of behavioural observations of emus, the consequences of parentage distribution, and theories about mating systems and sexual selection. The frequency of extra-pair copulations and intra-specific brood parasitism suggests patterns of descent that differ greatly from those implied by social monogamy. Received: 27 November 1999 / Received in revised form: 8 January 2000 / Accepted: 8 February 2000