The effect of workers size frequency distribution on colony development inBombus terrestris

Summary The effect of workers size frequency distribution on colony development was studied in 12 young colonies ofB. terrestris. By replacing the original workers with workers of determined size, colonies constituting small, large or mixed size nursing workers were created. The nursing workers size frequency distribution did not influence the average size of the newly emerged workers, nor their size frequency distribution. In contrast, the number of emerging workers and number of egg cells constructed by the queen in colonies with large workers were higher than in colonies with small workers. The small number of emerging workers is explained by prolonged duration of larval time in response to sub-optimal feeding in colonies of small workers. The higher number of egg cells constructed by the queens is supposed to be in response to the number of new cocoons available, or to better condition of the brood.     

Reproductive schedule and factors affecting soldier production in the eusocial bamboo aphid Pseudoregma bambucicola (Homoptera, Aphididae)

Summary: The reproductive characteristics of the soldier-producing aphid Pseudoregma bambucicola were studied in Kagoshima, Southern Japan, to know the factors affecting soldier production of eusocial aphids. The soldier proportion in aphid colonies was highest from October to November. In some large colonies, soldiers were observed in all seasons except in July when colony size was relatively small. Multiple regression analysis showed that the colony size was a principal factor affecting soldier proportion throughout a year. Other social or environmental factors such as aphid composition, host plant conditions and predator abundance were not always significant. Rearing experiments revealed that large colonies (̿,000 individuals) produced soldiers in almost all seasons while small colonies (<1,000) never produced any soldiers. The caste-production schedule of adult females was examined in the field. When solitary females produced both castes, they usually produced normal nymphs first and then soldiers. Females from large colonies tended to produce more soldiers in the earlier period of their lifetime, whereas females from newly established small colonies produced no or only a few soldiers at later times. The average number of soldiers and normal nymphs produced consecutively by a single female was >10 and >20, respectively. Because they have a small number of ovarioles (<15 on average), females should alter caste production within the same ovarioles according to changes in environmental conditions. Artificial removal or introduction of predators and reduction of colony size did not affect soldier production over two successive generations, revealing maternal effects on soldier production. Females cannot shift caste production quickly in response to changes in predator abundance and colony size. This is probably due to early developmental determination of castes within the mother's body.     

Taxonomy, distribution and nesting biology of species of the genus Dolichovespula (Hymenoptera, Vespidae)

The genus Dolichovespula consists provisionally of 18 species. Aerial nest site characteristics have been established for seven species but most of these species show flexibility in their choice of nest sites and two species often nest in shallow subterranean situations. Colony length is usually just over 3 months to approximately 4 months, but at lower latitudes may extend to more than 5 months. Mature colony size is usually approximately 1000 cells with more large cells than small cells. Parasitized colonies have a shorter colony cycle and smaller colonies. During the production of the sexual brood the larva/worker ratio reaches its lowest value of approximately 2.5 larvae per worker. Colonies often have upper mixed combs of small and large cells. Total adult production is usually less than 2000 adults. Colonies of D. arenaria and D. norwegica may specialize in mainly producing males or queens. Variations in mature colony size and production of queens is probably a consequence of the number of workers present, particularly early in the colony cycle.     

Polyandry and colony genetic structure in the primitive ant Nothomyrmecia macrops

The Australian endemic ant Nothomyrmecia macrops is considered one of the most ‘primitive’ among living ants. We investigated the genetic structure of colonies to determine queen mating frequencies and nestmate relatedness. An average of 18.8 individuals from each of 32 colonies, and sperm extracted from 34 foraging queens, were genotyped using five highly variable microsatellite markers. Queens were typically singly (65%) or doubly mated (30%), but triple mating (5%) also occurred. The mean effective number of male mates for queens was 1.37. No relationship between colony size and queen mate number was found. Nestmate workers were related by b=0.61 ± 0.03, significantly above the threshold under Hamilton’s rule over which, all else being equal, altruistic behaviour persists, but queens and their mates were unrelated. In 25% of the colonies we detected a few workers that could not have been produced by the resident queen, although there was no evidence for worker reproduction. Polyandry is for the first time recorded in a species with very small mature colonies, which is inconsistent with the sperm‐limitation hypothesis for the mediation of polyandry levels. Facultative polyandry is therefore not confined to the highly advanced ant genera, but may have arisen at an early stage in ant social evolution.     

Queen dimorphism and reproductive capacity in the ponerine ant, Ectatomma ruidum Roger

We report here the first case of queen dimorphism in a ponerine ant species. A total of 550 colonies of the Neotropical ponerine ant Ectatomma ruidum, from two natural populations in southeastern Mexico, were investigated for polymorphism and reproductive function within the queen caste. The distribution of different morphological traits (head and thorax widths, and scutum and alitrunk lengths) was shown to be bimodal. Thorax width and head width were significantly isometric for both macro- and microgynes and thorax proportions did not change with the category of the queen. Microgynes appear as an isometric reduction of the normal queens. On average, macrogynes were found to be approximately 20% larger in size and twice as heavy as microgynes (and up to three times heavier in terms of dry weight). Their wing surface was 72% greater. There was no difference between the two morphs in terms of their capacity to be inseminated and all dealate females present in natural colonies could be considered as true potentially reproductive queens whatever the class to which they belonged. Ovary size, number of ovarioles per ovary, and number of mature oocytes produced were significantly higher for macrogynes than for microgynes, but small queens were able to function as active egg-layers. However, the number of egg-laying individuals was significantly lower for this form, although egg-laying activity appeared to be independent of queen weight. Despite its markedly reduced reproductive capacity compared to macrogynes, the distribution of the microgyne form of E. ruidum in both studied populations was very broad, reaching one-third of all alate and dealate females and extending to one-third of all colonies. In 72.2% of the colonies where alate and/or dealate microgynes were present, both forms co-occurred. Fat content analysis results supported the idea that semi-claustral independent colony founding, typical for this species, would essentially be achieved by macrogynes, while microgynes would be adopted by established colonies. We argue that queen dimorphism in E. ruidum could represent an attractive alternative dispersal strategy for female sexuals. The small females may constitute an important reserve of potential reproductives at a very low energetic cost to the colony, the production of a macrogyne being about 7.5 times more costly than a microgyne. The significantly greater `wing surface/body weight' ratio of microgynes also suggests their greater capacity for dispersion. The combination of such a capacity for microgynes, along with their ability to contribute in the production of both female morphs, including the reproductively efficient macrogynes, would contribute to insuring genetic reassortment at the population level and could explain, in part, the ecological success of E. ruidum in Neotropical zones. Received: 4 January 1999 / Accepted: 12 May 1999     

Colony dynamics in a primitively eusocial halictine beeLasioglossum (Dialictus) zephyrum (Hymenoptera: Halictidae)

Summary Proximate control of colony dynamics was studied in the primitively eusocial halictine beeLasioglossum (Dialictus) zephyrum using allozyme markers. The results indicate that workers produce on average 15% of the male brood (range=0–50%) in small laboratory colonies made up of unrelated, single-generation, uninseminated females. This proportion is not influenced by colony size, but is influenced by the relative size of the queen. Large queens are more successful in dominating their workers than are small queens, the queen being defined as the female that is the mother of most of the brood produced in the colony. Older and larger females tend to become queens. Thus, while small differences in age (up to 4 days) influence which female becomes a queen, her ability to control her workers is primarily influenced by her relative size. The proportion of reproduction that is co-opted by the queen is negatively correlated with colony reproductivity (the number of males/day/female). Colony reproductivity is also negatively correlated with the standard deviation in size among females.     

Does insect mother know under what conditions it will make their offspring live?

According to the optimal oviposition theory, the larval success of insects depends on the oviposition site selection by females. Females are expected to choose a site with many resources and few competitors or predators to allow the best performance for their progeny, assuming that “mother knows best.” However, this is not systematically observed. The Aphidoletes aphidimyza larvae are generalist aphid predators and females consequently lay their eggs near or inside aphid colonies. The goal of this study was to investigate the impact of intraspecific competition on oviposition behavior of A. aphidimyza females. First, we counted the number of eggs laid by a female on a leaf with 20 aphids, in the presence of 0, 2, 4, or 6 conspecific eggs or in the absence of eggs but in presence of 3 virgin females. The same experiment was also performed under choice condition with 2 oviposition sites. Our results show that the presence of low densities of conspecific eggs, or the presence of conspecific females, have no significant impact on the number of eggs laid by A. aphidimyza females. One of the hypotheses advanced to explain these results is the advantages of conspecifics presence. At low densities, the presence of eggs on an oviposition site can indicate the suitability of the site for the females. The conspecific presence can also insure a dilution effect against predator and increase the presence of potential mating partners for this monogenic species.     

Growth or reproduction: Intrasexual competition in a colonial damselfishStegastes nigricans

Intrasexual competition within colonies of the damselfishStegastes nigricans was investigated. Both males and females held individual territories, and these territories were adjacently distributed, forming distinct conspecific colonies with different size compositions. In both large and small colonies, only relatively large individuals participated in reproduction. Breeding males and females left their territories to court, spawn and aggregate more frequently than non-breeders of the same colonies. Breeders were less frequently attacked by other fish during these excursions than were non-breeders. Most attacks were conducted by breeders of the same sex. This intrasexual aggression may suppress the reproduction of non-breeders at least in large colonies. Non-breeders in large colonies had smaller gonads than breeders of both large and small colonies, but they grew faster than breeders of the same body size in small colonies. This suggests that non-breeders in large colonies allocate energy to growth in order to be reproductively competitive in the future, although only a few of them remained in the same colonies upon maturity. Colony size thus has an effect on the reproductive life histories of individual damselfish.     

Forager abundance and its relationship with colony activity level in three species of South American Pogonomyrmex harvester ants

The proportion of foragers in ant colonies is a fairly constant species-specific characteristic that could be determined by intrinsic or extrinsic factors. If intrinsic factors are relevant, species with similar life history characteristics (e.g., colony size and foraging strategies) would be expected to have a similar proportion of foragers in their colonies. Within the genus Pogonomyrmex, North American species can vary largely in their colony size, whereas only species with small colonies are known in South America. We studied the characteristics of the foraging subcaste in three sympatric South American species of Pogonomyrmex harvester ants, and compared it with the available information on other species of the same genus. We used two mark-recapture methods and colony excavations to estimate the number and proportion of foragers in the colonies of P. mendozanus, P. inermis, and P. rastratus, and to test the relationship between forager external activity levels and abundance per colony. Forager abundance in the three studied species was lower than in most North American species. The percentage of foragers in their colonies ranged 7–15 %, more similar to North American species with large colonies than to those with small colony size. Foraging activity was positively correlated with forager abundance in all three species, implying that colony allocation to number of foragers allows for higher food acquisition. Further comparative studies involving a wider range of traits in South and North American species would allow to unveil the role of environmental factors in shaping each species’ particular traits.     

Stochastic effects in LMC models.

LMC (local mate competition) was first introduced by W. D. Hamilton to explain extraordinary female-biased sex ratios observed in a variety of insects and mites. In the original model, the population is subdivided into an infinite number of colonies founded by a fixed number of inseminated females producing the same very large number of offspring. The male offspring compete within the colonies to inseminate the female offspring and then these disperse at random to found new colonies. An unbeatable sex ratio strategy is found to be female-biased. In this paper, the effects of having colonies of random size and foundresses producing a random finite number of offspring are considered. The exact evolutionarily stable strategy (ESS) sex ratio is deduced and comparisons with previous approximate or numerical results are made. As the mean or the variance of brood size increases, the ESS sex ratio becomes more female-biased. An increase in the variance of colony size increases the ESS proportion of males when the mean brood size and colony size are both small, but decreases this proportion when the mean brood size or the mean colony size is large.     

Reproductivity and relatedness in a communal halictine beeLasioglossum (Chilalictus) hemichalceum

Summary The biology of communal species is not well known. Here we report the reproductivity (number of offspring per female) and genetic relatedness forLasioglossum (Chilalictus) hemichalceum, a communal halictine bee. There is a positive Model II regression, with a slope indistinguishable from one, between natural logarithms of the number of offspring and the number of adult females in a colony; indicating that as colony size increases the reproductivity per female does not decrease. This pattern is like that found in one other communal species and unlike that found in a wide variety of eusocial species. Relatedness among adult nestmates, based on two variable loci, is low. For 52 colonies it is about 0.13, and for a subset of 25 reproductively active colonies it was not distinguishable from zero. This indicates that the role of kin selection is minor at best in this highly cooperative, communal species. A review of the relatedness data available for communal groups, both foundress associations and species that are communal throughout their colony cycle, indicates that communal sociality is often but not always associated with low intra colony relatedness.     

Courtship Disruptions and Male Mating Strategies: Examples from Female-Defense Mating Systems

Males frequently interrupt the copulation attempts of other males, and these courtship disruptions may limit the extent to which a few males are able to monopolize mating access to females. Males actively defend sexually receptive females in many species in which females form dense aggregations during the breeding season. Across and within such species there is considerable variation in the mating tactics adopted by males, with males in some cases defending groups of females and in other cases sequentially consorting with individual females. Colonial blackbirds have been central to studying this mating system, and we develop a conceptual model for how courtship disruption may account for variation in male mating tactics in this group. Our model assumes that the frequency of disruptions increases with greater colony size. As a consequence, successful copulations are less likely to occur at large colonies than at small colonies, and males are expected to switch from defending multiple females at the colony to consorting individual females away from it. Results from two species of blackbird support the basic assumptions of this model. In one species, the Montezuma oropendola, disruptions occur rarely and males defend groups of females, whereas in the other species, the yellow-rumped cacique, disruptions are frequent and males defend single females. Moreover, consistent with a key prediction, within each species, males associated with small colonies remain at the colony and defend groups of females, whereas males spend little time defending groups of females at large colonies and rarely attempt copulations there. This model has the potential to explain variation in male mating strategies and female monopolization for other taxa in which females form breeding aggregations.     

Sociality and sex allocation in an Australian allodapine bee Braunsapis protuberans

Abstract  Herein the first detailed study of sociality and life history in an Australian species of the allodapine bee genus Braunsapis is provided. Colonies of B. protuberans were sampled from the Great Sandy National Park in Queensland from late winter until later summer. Single-female colonies appear to have suffered substantially higher rates of total brood loss, or failure to produce brood, than multifemale colonies, but rearing efficiency in colonies with at least some brood did not differ between these two colony types. There was marked reproductive skew in multifemale colonies and ovary size was strongly linked to relative body size. However, females with smaller body size and smaller ovaries also had lower levels of wing wear, suggesting that they do not specialise in foraging. These patterns are similar to an African species, Braunsapis vitrea , and suggest that colonies may principally comprise a dominant reproductive female who provides food for her juvenile offspring, along with a variable number of subordinate females who may be waiting to inherit their natal nest in the event of their mother's death. However, it is likely that in such events, the remaining female(s) will care for orphaned brood as some single-female colonies contained substantial older brood, even though the sole female had little or no wing wear. Such alloparental care in the case of orphaning may help explain the high level of female bias in sex ratios.     

Foraging decisions of individual workers vary with colony size in the greenhead ant Rhytidoponera metallica (Formicidae, Ectatomminae)

Summary. The ability of worker ants to adapt their behaviour depending on the social environment of the colony is imperative for colony growth and survival. In this study we use the greenhead ant Rhytidoponera metallica to test for a relationship between colony size and foraging behaviour. We controlled for possible confounding ontogenetic and age effects by splitting large colonies into small and large colony fragments. Large and small colonies differed in worker number but not worker relatedness or worker/brood ratios. Differences in foraging activity were tested in the context of single foraging cycles with and without the opportunity to retrieve food. We found that workers from large colonies foraged for longer distances and spent more time outside the nest than foragers from small colonies. However, foragers from large and small colonies retrieved the first prey item they contacted, irrespective of prey size. Our results show that in R. metallica, foraging decisions made outside the nest by individual workers are related to the size of their colony.Received 23 March 2004; revised 3 June 2004; accepted 4 June 2004.     

Variation in resource size distribution around colonies changes ant–parasitoid interactions

The distribution of resources within habitats affects species abundance, richness and composition, but the role of resource distribution in species interactions is rarely studied. In ant communities, changes in resource distribution within habitats may influence behavioral interactions because many ant species are specialized to efficiently harvest a subset of available resources. This study investigates whether interactions between the behaviorally dominant host ant Pheidole diversipilosa and its specialist parasitoid (Phoridae: Apocephalus orthocladus) depend on resource size distribution around the colony. Using in situ foraging arenas to manipulate parasitoid abundance and resource size distribution around colonies, we tested whether variation in resource size distribution allows P. diversipilosa to alter its foraging behavior in ways that lessen the impact of parasitoid attack. P. diversipilosa colonies do not lower the impact of parasitoid attack by increasing the number of workers foraging individually on small and widely dispersed resources. However, the presence of multiple large resources allows colonies to temporarily redistribute soldier ants from resources patrolled by parasitoids to other resources not patrolled by parasitoids, and to maintain soldier abundance at levels found in the absence of parasitoids. These results highlight the importance of placing behavioral interactions within the context of variation in resource distribution.     

The influence of social structure on brood survival and development in a socially polymorphic ant: insights from a cross‐fostering experiment

Animal societies vary in the number of breeders per group, which affects many socially and ecologically relevant traits. In several social insect species, including our study species Formica selysi, the presence of either one or multiple reproducing females per colony is generally associated with differences in a suite of traits such as the body size of individuals. However, the proximate mechanisms and ontogenetic processes generating such differences between social structures are poorly known. Here, we cross‐fostered eggs originating from single‐queen (= monogynous) or multiple‐queen (= polygynous) colonies into experimental groups of workers from each social structure to investigate whether differences in offspring survival, development time and body size are shaped by the genotype and/or prefoster maternal effects present in the eggs, or by the social origin of the rearing workers. Eggs produced by polygynous queens were more likely to survive to adulthood than eggs from monogynous queens, regardless of the social origin of the rearing workers. However, brood from monogynous queens grew faster than brood from polygynous queens. The social origin of the rearing workers influenced the probability of brood survival, with workers from monogynous colonies rearing more brood to adulthood than workers from polygynous colonies. The social origin of eggs or rearing workers had no significant effect on the head size of the resulting workers in our standardized laboratory conditions. Overall, the social backgrounds of the parents and of the rearing workers appear to shape distinct survival and developmental traits of ant brood.     

Male-male Competition and Female Mate Choice through Courtship Display in the Territorial Damselfish Stegastes nigricans

Both sexes of the herbivorous damselfish Stegastes nigricans maintain individual feeding territories. These territories are distributed contiguously, forming distinct colonies. Females visit male territories to spawn, and eggs are guarded by males until hatching. Male-male competition and female mate choice were studied in two colonies of different size compositions. Only larger individuals bred in both colonies. Some males in the large colony, that were larger than the breeding males in the small colony, did not succeed in reproducing probably because of severe attacks by the larger males while courting. However, females did not choose large size among breeding males. The most important male characteristic in female choice was the frequency of courtship displays in both colonies. Females in the large colony chose males mainly on the basis of the frequency of displays conducted in the females' territories, whereas females in the small colony chose males on the basis of the frequency of displays conducted in the males' territories. This difference may be a result of the difference in colony size. The distances between females' and males' territories were much greater in the large colony, and, because females cannot see courtship displays conducted in distant male territories, males in the large colony may have had to visit female territories frequently in order to conduct courtship near the females.     

Social organization, reproductive behavior and ecology of Leptothorax acervorum (Hymenoptera, Formicidae) from the Sierra de Albarracin in central Spain

Summary: Leptothorax acervorum, an ant species with holarctic range, occurs in an isolated population in the Spanish Sierra de Albarracin. Dissection of dealate females and laboratory observations revealed that in contrast to other European populations, the colonies are monogynous, with one reproductive queen each and a variable number of virgin or mated dealate but not laying females. Most of the latter probably just hibernate in the mother nests, leaving them in the following spring, but a few remain there for longer time, without reproducing. Such colonies then are functionally monogynous. Alate females exhibit a stationary sexual calling, and mating behavior could be studied in the laboratory. Mated females return to the mother nest where they soon shed wings. When developing fertility before or after hibernation they are evicted from the nests; in nature they probably form daughter colonies. Patchy habitat and rough climatic conditions in the Sierra de Albarracin may be responsible for the particular reproductive behavior of L. acervorum in this area. The generally small size difference between queens and workers in the subgenus Leptothorax entails high costs of dispersal and colony foundation by single queens who have to forage for their first brood. Some kind of dependent colony foundation therefore is frequently met with in the subgenus. Notwithstanding the marked biological and a few slight morphological differences between central European L. acervorum and the Spanish population its taxonomic status as yet is unsettled. We refer to this population provisionally as "L. acervorum Albarracin".     

Spawning dynamics of orange roughy,Hoplostethus atlanticus,in mid-slope waters of New Zealand

Synopsis The social and reproductive biology of the sand tilefish,Malacanthus plumieri (Malacanthidae), was studied at Glover's Reef, Belize, where this species occurs in colonies over sand-rubble flats. Individuals each occupy a home burrow refuge and a surrounding home range. Home range overlap among adjacent fish of the same sex is low, and individuals defend exclusive use of much of their home range against all conspecifics except mates (i.e., territoriality). Areas defended by males overlap the territories of up to 6 females; and male territory area is positively related to the number of female residents. Males maintain dominance over females within their territories by aggression, including intervention into some female disputes. Females spawn pelagically-dispersed eggs as frequently as every day. Each female spawns near her burrow, almost exclusively with the male whose defended area encompasses her territory (harem polygyny). Tilefish colonies therefore consist of a mosaic of female territories over which adjacent male territories are superimposed. Histological evidence and observation of behavioral sex change in one female revealed thatM. plumieri is capable of protogynous sex reversal. Females did not change sex in response to removal of one male. Occurrence of small transitional fish indicates that the onset of sex change is controlled by factors other than size-related social hierarchies within harems or colonies.