Nestmate discrimination in social wasps (Polistes metricus,Hymenoptera: Vespidae)

Summary Laboratory-overwintered paper wasp (Polistes metricus) females preferentially associate on new nests with former nestmates (presumably their sisters) rather than with non-nestmates in the absence of cues associated with their natal nests or nest sites. Females isolated from conspecifics and nests for 74–99 days retain the ability to discriminate nestmates from nonnestmates.     

Relatedness among nestmates in a primitively social wasp,Cerceris antipodes (Hymenoptera: Sphecidae)

Summary Kin selection, acting through high levels of relatedness, may be an important promoter in the evolution of nest sharing. Cerceris antipodes is a sphecid wasp that shares nests in contrast to the majority of sphecids where only one female occupies a nest. Nest sharing results from females remaining in their natal nests and females moving to already occupied nests. Average relatedness among nestmates of C. antipodes was calculated from allele frequencies of phosphoglucomutase to determine whether nests were usually shared by close relatives. Relatedness among nestmates was high (0.5 to 0.6) at one aggregation in two consecutive years. Preferential association of relatives away from the natal nest can be inferred from these high values combined with the frequency of nest switching observed. Estimates of relatedness were lower (about 0.3) and associated with large standard errors at 3 other aggregations. Inbreeding and relatedness between neighbouring nests were only significant at the aggregation with the fewest females. This may be a result of the small effective population size. The levels of relatedness observed are consistent with kin selection through relatedness being an important factor in the evolution of nest sharing.     

The mechanism of nestmate discrimination in the tropical social wasp Ropalidia marginata and its implications for the evolution of sociality

Summary We have demonstrated that females of the primitively eusocial tropical wasp Ropalidia marginata can discriminate nestmates from nonnestmates outside the context of their nests. This was accomplished by recroding all behavioural interactions in a neutral arena and comparing tolerance levels. In order for these wasps to make such a discrimination, however, it was essential that after eclosion both the discriminated and the discriminating animals were exposed to their respective natal nests and nestmates. The results suggest that both recognition labels and templates are acquired by the animals from sources outside their body, perhaps from their nest or nestmates. It is thus unlikely that different genetic lines within a colony can be distinguished. We conclude, therefore, that genetic asymmetries created by haplodiploidy, but often broken down by multiple mating and polygyny, are not restored by preferential altruism towards full rather than half sisters by means of kin recognition. Hence we recommend caution in ascribing the multiple origins of eusociality in the Hymenoptera to haplodiploidy.     

Trophic aspects of caste determination in Halictus ligatus,a primitively eusocial sweat bee

Caste determination in primitively eusocial sweat bees is thought to be due to an interacting suite of factors, including size of the larval provision mass, time of year, and social context of the nest into which a young female emerges. Newly emerged gynes are significantly fatter than newly emerged workers, suggesting the existence of larval caste determination cues. Since photoperiod, temperature, and interactions with nestmates were unlikely to affect larval caste determination, we compared the sizes and contents of larval provision masses destined to produce either workers or gynes. Gyne-destined larvae consumed pollen masses that were larger and contained slightly more sugar than those of worker-destined larvae. We suggest that sugar content is one cue which prompts the development of fat reserves in gyne-destined females but not in worker-destined females. The amount of fat possessed by a newly emerged female influences her chances of successfully entering diapause shortly after emergence. Therefore, small, lean females may be more susceptible to behavioural control by queens and more likely to become workers, while large, fat females would be more likely to become gynes. Correspondence to: M.H. Richards     

Dispersal decisions and predispersal behavior in <Emphasis Type="Italic">Polistes</Emphasis> paper wasp ‘workers’

Social insects are popular models for studying the evolution of cooperation. Casteless taxa where individuals have the flexibility to either nest alone or cooperate are particularly valuable for understanding the causes and consequences of cooperative behavior. For example, some ‘workers’ from Polistes paper wasp nests disappear from their natal colony soon after pupal emergence and nest independently. However, little is known about dispersal behavior. In this paper, I compare predispersal behavior of wasps who leave their natal colony soon after emergence with behavior of individuals who remain on the natal colony as true workers. I found that P. dominulus females with short nest tenure behave much like gynes (reproductive-destined offspring produced at the end of the season), as wasps with short nest tenure are behaviorally selfish while on the natal colony. They spend a smaller proportion of their time foraging and a larger proportion of their time resting than workers with long nest tenure. In addition, I assessed the factors that may favor early dispersal. Nest environment strongly influenced dispersal; large colonies had a smaller proportion of females with short nest tenure. Queen turnover also increased dispersal behavior perhaps because queen turnover reduces relatedness between a colony’s current and future offspring, thereby reducing the kin-selected benefits of cooperation. Therefore, casteless social insects exhibit a surprising degree of reproductive flexibility. Individuals may use information about their internal state and nest environment to optimize their behavioral strategies.     

Effects of stage of colony cycle,context, and intercolony distance on conspecific tolerance by paper wasps (Polistes fuscatus)

Summary We observed in the field how resident females of the social wasp, Polistes fuscatus, treated female nestmates, non-nestmate first cousins, and unrelated non-nestmates. Behavioral observations were made 1, 3, 4, 6, 7, 8, and 11 weeks after the emergence of a colony's first workers. Resident females were highly tolerant of female nestmates but highly intolerant of unrelated non-nestmates throughout the post-worker-emergence phase of the colony cycle. First cousins were treated either highly tolerantly or highly intolerantly, although most cousins ( 63%) were treated highly intolerantly. The treatment of cousins suggests that they are treated either tolerantly (like nestmates) or intolerantly (like unrelated non-nestmates) depending on whether they fall above or below an acceptance threshold, respectively. Resident females did not significantly change their tolerance nestmates, first cousins, and unrelated females between different observation periods. However, all conspecifics were generally treated the most intolerantly 11 weeks post-worker-emergence, a time in the colony cycle when combs no longer contain brood. This decreased tolerance and its associated variance patterns late in the colony cycle are consistent with a more restrictive acceptance threshold. The optimal level of the acceptance threshold appears to be a compromise between the fitness consequences of accepting unrelated non-nestmates and rejecting one's nestmates. In a laboratory study, resident females were equally tolerant of female nestmates on and off the comb but significantly less tolerant of unrelated females on the comb than off the comb. Thus, females can modify their tolerance rapidly in different recognition contexts. In a second laboratory study, resident females were equally intolerant of unrelated females, regardless of whether they were from colonies 50 m or 50 km distant.Offprint requests to: G.J. Gamboa     

Nestmate recognition in three species of stenogastrine wasps (Hymenoptera,Vespidae)

The capacity to recognise a conspecific intruder was investigated in Parischnogaster jacobsoni, Liostenogaster flavolineata and L. vechti, three species of primitively social wasps of the subfamily Stenogastrinae. Results of behavioural experiments carried out in the field showed that females of all three species react pacifically if presented with female nestmates, but aggressively reject an intruder from a conspecific colony. As L. flavolineata and L. vechti both build large clusters of nests, often very close to each other, the recognition capacity among females from different nests, but in the same conspecific cluster, was also investigated. Females of both species were more aggressive towards females from a different colony in the same cluster than towards their female nestmates. Additional experiments on L. flavolineata showed that there was no difference in reaction towards females from colonies nearer or further from the tested colony but within the same cluster, nor towards females from a different cluster. The capacity to recognise an alien conspecific nest containing immature brood was investigated in P. jacobsoni. Adult females of this species, invited to land on an alien nest which had experimentally been exchanged for their own, accepted the new nest and partially destroyed the immature brood. The behaviour of the females when they land on an alien nest, however, suggests that they do recognise the nest as foreign. Acceptance of foreign nests coupled with low immature brood destruction is probably due to the high energetic costs of egg-deposition and larval rearing in stenogastrine wasps. These results suggest that nestmate recognition in these wasps is very efficient, even though they belong to the most primitive subfamily of social wasps. Received: 16 April 1996/Accepted after revision: 9 August 1996     

Kin discriminators in the eusocial sweat bee <Emphasis Type="Italic">Lasioglossum malachurum</Emphasis>: the reliability of cuticular and Dufour’s gland odours

The ability to discriminate degrees of relatedness may be expected to evolve if it allows unreciprocated altruism to be preferentially directed towards kin (Hamilton in J Theor Biol 7:1–16, 1964). We explored the possibility of kin recognition in the primitively eusocial halictid bee Lasioglossum malachurum by investigating the reliability of worker odour cues that can be perceived by workers to act as indicators of either nest membership or kinship. Cuticular and Dufour’s gland compounds varied significantly among colonies of L. malachurum, providing the potential for nestmate discrimination. A significant, though weak, negative correlation between chemical distance and genetic relatedness (r = −0.055, p < 0.001) suggests a genetic component to variation in cuticular bouquet, but odour cues were not informative enough to discriminate between different degrees of relatedness within nests. This pattern of variation was similar for Dufour’s gland bouquets. The presence of unrelated individuals within nests that are not chemically different from their nestmates suggests that the discrimination system of L. malachurum is prone to acceptance errors. Compounds produced by colony members are likely combined to generate a gestalt colony chemical signature such that all nestmates have a similar smell. The correlation between odour cues and nest membership was greater for perceived compounds than for non-perceived compounds, suggesting that variability in perceived compounds is a result of positive selection for nestmate recognition despite potentially stabilising selection to reduce variability in odour differences and thereby to reduce costs derived from excessive intracolony nepotistic behaviour.     

Behavioral evidence for population structure in Lasioglossum (Dialictus) zephyrum female dispersion patterns

Summary Within-aggregation nest distribution and behavioral interactions between pairs of female Lasioglossum zephyrum were investigated. Within aggregations, nests are contagiously distributed (clumped), and this distribution is not correlated with the particle size of the soil surface. Results of behavioral interactions both in the field and laboratory show that females residing near one another behave as if they are more closely related than females residing at greater distances from one another. The behaviors used are known to be correlated with the degree of relatedness between females. This suggests that females found colonies near their natal nests, producing neighborhoods of related colonies within aggregations of L. zephyrus.     

Is kin cooperation going on undetected in marine bird colonies?

In multitudinous breeding colonies, kin interactions could go unnoticed because we are unaware of the kinship among adults we observe. Evidence of cooperation and competition between close adult kin in a blue-footed booby colony was sought by analyzing patterns of natal dispersal and proximity of nests. Male and female recruits nested closer to their own natal sites than to their parents’ current sites. Males (only) dispersed less far when both parents were present than when no parent or one parent was present, but not selectively close to fathers versus mothers when these were divorced. Neither parental presence nor parental proximity affected breeding success of recruits of either sex. Although distances between the nests of simultaneously recruiting broodmates were unrelated to their sex, males dispersed 13.1 m less when a sister was present than when a brother was present. Neither sex was affected in its dispersal distance by the presence or hatching order/dominance of a broodmate. Neither sex was affected in its breeding success by the presence versus absence of a broodmate, although female success increased with proximity of their brothers. Parents and sisters may actively or passively help males establish their first territories near their natal sites and nearby brothers may help females in their first breeding attempts; otherwise, boobies do not influence each other’s natal dispersal and first breeding success. It appears that boobies do not nest selectively close to or far from their parents, offspring, or broodmates. Why there is apparently so little cooperation and altruism between close adult relatives in booby colonies is puzzling.     

Extended family structure in the ant Formica paralugubris: the role of the breeding system

In populations of various ant species, many queens reproduce in the same nest (polygyny), and colony boundaries appear to be absent with individuals able to move freely between nests (unicoloniality). Such societies depart strongly from a simple family structure and pose a potential challenge to kin selection theory, because high queen number coupled with unrestricted gene flow among nests should result in levels of relatedness among nestmates close to zero. This study investigated the breeding system and genetic structure of a highly polygynous and largely unicolonial population of the wood ant Formica paralugubris. A microsatellite analysis revealed that nestmate workers, reproductive queens and reproductive males (the queens' mates) are all equally related to each other, with relatedness estimates centring around 0.14. This suggests that most of the queens and males reproducing in the study population had mated within or close to their natal nest, and that the queens did not disperse far after mating. We developed a theoretical model to investigate how the breeding system affects the relatedness structure of polygynous colonies. By combining the model and our empirical data, it was estimated that about 99.8% of the reproducing queens and males originated from within the nest, or from a nearby nest. This high rate of local mating and the rarity of long-distance dispersal maintain significant relatedness among nestmates, and contrast with the common view that unicoloniality is coupled with unrestricted gene flow among nests. Received: 8 February 1999 / Received in revised form: 15 June 1999 / Accepted: 19 June 1999     

Foraging decisions of American robins: somatic and reproductive tradeoffs

Summary Breeding units (occupants of a nest including at least one reproductive female) within two free-living populations of the prairie vole, Microtus ochrogaster, were monitored by live-trapping at nest during two 28-h periods each week from October 1980 to March 1984. Data are presented for 281 breeding units from all seasons, at high and low population densities and during breeding and nonbreeding periods. Fifty percent of the breeding units were monogamous (single resident reproductive male and female), 27% consisted of a single reproductive female with no resident adult male and 23% included more than one resident adult male and/or female (complex units). Monogamous units were present in the same proportions during breeding and nonbreeding periods. The number of monogamous units was significantly greater at low population densities than at high densities. During winter there were relatively more complex units and fewer single female units than during the rest of the year. Monogamous pairs remained together for an average of 42 days. Seventy-eight percent of these pairs were disbanded by the death of one or both members. There were few overlaps of the home ranges of adjacent breeding units. Significantly more nests were visited by nonresident males than by females, and the intervals between visits by males were significantly shorter than those for visits by females. Males visited single female units significantly more often than units with one or more resident males. Survival of juveniles was generally very low; 38% and 34% of young males and females, respectively, that were trapped survived until 30 days of age. Of young females remaining at the natal nest at low population densities, only 17.6% were reproductively activated; 77.1% of such females became reproductively activated at high densities. All young females that dispersed from the natal nest became reproductive.     

Caste determination and differential diapause within the first brood of Halictus rubicundus in New York (Hymenoptera: Halictidae)

Summary The partially bivoltine, primitively eusocial sweat bee Halictus rubicundus produces two female castes, gynes and non-gynes, in its first brood in New York. Castes in this brood differentiate within the first few days of adult life, with gynes leaving the population to overwinter as early as mid-June (non-gynes further differentiate into replacement queen and worker subcastes, with older females typically dominant). Analysis of possible mechanisms of caste determination reveals that although gynes average significantly larger than non-gynes within the first brood, this appears largely due to a late mean emergence data coupled with an increase in the size of emerging females over the course of brood emergence, rather than a causal relationship. A strong correspondence between male abundance (relative to newly-emerged females) and the pattern of gyne production, along with data from dissections, suggests that females that mate when young become diapausing gynes, while those that do not mate promptly become non-gynes and do not diapause even though many mate later. Although alternatives to this simple mechanism cannot be ruled out entirely, it nevertheless offers profound implications for theoretical and empirical understanding of the evolutionary origins of the worker caste.     

Rules of supply and demand regulate recruitment to food in an ant society

The process by which ant scouts move a group of nestmates toward a newly discovered food site is called recruitment. In this paper, I report on the interactions between scouts and nestmates that result in a graded recruitment response to graded food quality in the fire ant, Solenopsis invicta. Twelve experimental groups composed of 100 fire ant workers and 50 fire ant larvae were established (three experimental groups per colony × four stock colonies). Each experimental group was placed in a shallow, artificial nest with a glass cover. After a 48-h period of food deprivation, experimental groups were exposed to one of three concentrations of sugar water. Behavioral interactions between scouts and nestmates in each group were videotaped at 10× magnification for 20 min. Detailed behavioral data on a total of 120 scouts (10 scouts per experimental group) and ~1,000 nestmates (~90 nestmates per experimental group) were transcribed from the videotapes using standard play and frame-by-frame techniques. Throughout the recruitment process, scouts employed six discrete behaviors to inform nestmates of the location and quality of a food site. Scouts laid incoming trails, waggled their heads, increased walking tempo, stroked nestmates with their antennae, advertised with a brief food display, and led groups of nestmates to the food site by laying outgoing trails. In turn, nestmates assessed the food sample with antennae, then responded to or resisted recruitment based on the quality of food advertised, their employment status and their level of hunger. In summary, recruitment was an emergent property based on competent supply and demand decisions made face-to-face inside the nest rather than on the trail or at the food site.Communicated by J. Heinze     

Natal dispersal and philopatry in prairie voles (Microtus ochrogaster) in relation to population density,season, and natal social environment

Summary We used intensive livetrapping to examine natal dispersal and philopatry in prairie voles (Microtus ochrogaster). The majority of male (70.0%) and female prairie voles (75.1 %) remained at the natal nest until death. Those males and females that did disperse left home at about the same age (45–55 days) and moved similar distances (28–33 m). Dispersal was more common (1) from small natal groups than from large natal groups, (2) following disappearance of parents, (3) during the breeding period than during the nonbreeding period, and (4) at low population densities than at high densities. Dispersal was not associated with level of competition for mates within natal groups, and dispersers did not differ from nondispersers in body weight. Our data do not support competition for mates or resources as important factors influencing natal dispersal in prairie voles. The absence of sex differences in dispersal tendency or distance, and our fording that more than half of dispersers had become reproductive before leaving the natal nest, lead us to suggest that inbreeding avoidance is not a primary function of dispersal in this species. Dispersal was, however, more common when potential mates within the natal group were relatives than when they were nonrelatives. Although not tested here, if family members avoid mating with one another through patterns of mate choice, then some animals may leave home in search of mates. The precise benefits associated with philopatry in prairie voles remain to be identified. Correspondence to: B. McGuire at her present address     

Parental investment in two solitary wasps Ancistrocerus adiabatus and Euodynerus foraminatus (Eumenidae: Hymenoptera)

Summary Females of the solitary eumenid wasps Ancistrocerus adiabatus and Euodynerus foraminatus control the adult size of their offspring by the amount of food provded to the larvae. For both species, larger females provision more offspring and collect more food than smaller females. Males of E. foraminatus, upon emergence as adults, fight for control of the nest area. The winning brother remains at the nest and mates with his sisters as they emerge several days later. Males of A. adiabatus are not as agonistic as males of E. foraminatus so that a number of males may remain near the natal nest. When females nest near each other, male-male interactions increase, and the likelihood of sibling mating decreases. Under conditions of clumped nesting, females make larger offspring and invest more in males than when nesting in isolation.     

Strategic exploitation in a socially parasitic bee: a benefit in waiting?

Social parasitism has evolved at least ten times in the allodapine bees but studies that explore the parasite’s integration and exploitation of host colonies are lacking. Using colony content and dissection data, we examine how Inquilina schwarzi affects the social organisation of its host Exoneura robusta. Our samples include three critical periods in the host life cycle: initial formation of dominance hierarchies in late autumn, commencement of oviposition by host queens in late winter, and development of secondary reproductives in late spring. I. schwarzi preferentially parasitises larger host colonies in autumn, but during autumn and winter, the parasite appears to be socially invisible, living in the nest without disrupting the normal functioning of these colonies. Inquilines begin egg laying much later than their hosts, and by late spring, they have disrupted host reproductive hierarchies, leading to lower skew in ovarian sizes of their host nestmates. Living invisibly within the host nest for the first 6 months and waiting until well after host reproduction has begun before disrupting their social organisation appear to be unique among social insects. Such a change in strategy may be facilitated by the different social systems found in allodapine bees, with the social parasites possibly disrupting the reproductive hierarchies during spring to prevent or reduce the normal dispersal of some host females from their natal nests.     

Why do female Belding's ground squirrels disperse away from food resources?

We examined the effects of food provisioning on the natal dispersal behavior of Belding's ground squirrels (Spermophilus beldingi). We provided extra food to adult and yearling females in their maternal territories during pregnancy and lactation, and to offspring of these females in their natal areas for 6 weeks after weaning. We used unprovisioned young of unprovisioned mothers as controls. Provisioning influenced the probability of dispersal from the natal area by female but not male S. beldingi. All surviving male S.␣beldingi dispersed by 55 weeks of age, regardless of whether they and their mothers received extra food. By contrast, we observed a significant trend, beginning 3 weeks after weaning and continuing through the yearling year, for a greater proportion of provisioned than control female S. beldingi to emigrate from the natal area. Competition for food did not appear to influence natal dispersal of females. However, overall population density, density of females weaning litters, and rates of aggression and vigilance among these females, were higher in provisioned than control areas, suggesting that competition for non-food resources was unusually intense in provisioned areas. We propose that juvenile female, but not juvenile male, S. beldingi may emigrate from the natal site to increase access to areas with low densities of conspecifics. Together with findings of earlier workers, our results suggest that spatial and temporal distributions of environmental resources are important influences on the dispersal behavior of female ground squirrels. Received: 28 February 1996 / Accepted after revision: 16 October 1996     

Philopatry and mother-daughter associations in bushy-tailed woodrats: space use and reproductive success

Social groups in mammals are often based on overlapping generations of philopatric females, yet few researchers have examined fitness consequences of associations between females and their daughters. We examined survival and reproductive consequences of sharing a natal site with one's mother or daughter in wild bushy-tailed woodrats (Neotoma cinerea). Bushy-tailed woodrats reside on discrete rocky outcrops, and females tend to spend their entire reproductive life on their natal outcrop. Mothers and daughters that co-existed on the natal outcrop were closely associated in space. Juvenile females were more likely to survive their first winter to become breeding yearlings at their natal site if their mother was also present at the natal site during the winter. Juveniles survived equally well with or without their mother where densities of adult females were experimentally reduced, suggesting that females enhance their daughter's survival by facilitating their access to limited resources. Yearling females exhibited no reproductive costs from association with their mothers at the natal site during the breeding season; in fact, yearlings that bred at the natal site simultaneously with their adult mothers tended (P = 0.07) to experience fewer reproductive failures than did those that bred in the absence of their mothers. Mothers did not experience any detectable costs when sharing a natal site with a daughter. We conclude that bushy-tailed woodrats exhibit stable, fitness-enhancing associations among mothers and their philopatric daughters.     

Subordinate males are more likely to help if unrelated to the breeding female in cooperatively breeding white-browed scrubwrens

Subordinates in communally breeding groups of birds usually help to provision nestlings, but in some species helping-at-the-nest is facultative. In species in which groups usually contain relatives, subordinates either always feed young or are more likely to do so when breeding dominants are close relatives, suggesting that benefits of helping collateral kin are important. In other species, adult group members are unrelated to each other and males may only feed young if they have gained paternity, showing that cooperation is related to the mating system. The white-browed scrubwren, Sericornis frontalis, is a communally breeding species in which most groups consist of a simple pair or a dominant pair with a subordinate male. Subordinate males either fed nestlings in a given nest at a rate comparable to the dominants, or did not feed them at all. Breeding groups usually formed through natal philopatry of males, so that about 80% of subordinates were closely related to one or both members of the dominant pair. However, because of death and dispersal, 54% of subordinates were unrelated to the resident female. Although subordinates with their mother fed nestlings in 48% of cases, they fed offspring in 75% of cases if their mother had been replaced by an unrelated female, suggesting that their decision to help is influenced by the opportunity to mate with the female. Supporting this conclusion, relatedness to the dominant male did not affect subordinate behaviour, and genetic studies showed that subordinates often gained paternity if unrelated to the female. Thus, paradoxically, provisioning nestlings is related to the opportunity for mating in a society in which there is natal philopatry and subordinates are usually related to one or both members of the dominant pair. Received: 25 January 1997 / Accepted after revision: 1 May 1997