Deceptive pollination of the Lady's Slipper Cypripedium tibeticum (Orchidaceae)

To test whether the nectarless flowers of Cypripedium tibeticum attract pollinators through mimicry like the allied species C. macranthos var. rebunense, pollination biology of C. tibeticum was investigated in western China. Although C. tibeticum was also pollinated by bumble bee queens, i.e. Bombus lepidus , B. lucorum and B. hypnorum , no special, rewarding model plants were found in the habitat. Field experimentation confirmed that the flowers were self-compatible but insects were required to transfer orchid pollen to the stigma. Both Bombus queens and workers were visitors, but queens were much more frequent than workers and only queens were effective pollinators. Floral functional morphology analysis showed that it was large queens rather than small workers that fitted well with the flowers of C. tibeticum. With the faint sweet-fruity scent, the minor floral fragrance compound, ethyl acetate, probably plays a role in attracting bumble bees by food deception. The dark flowers with the inflated, trap-like labellum are hypothesized to mimic the nest site of queens. Therefore, bumble bee queens tend to be attracted by C. tibeticum through nest site mimic combined with food deception. Considering that the co-blooming flowers of C. flavum are pollinated by the Bombus workers, and C. smithii pollinated by a queen, we suggest that using the same bumblebees with different body sizes as the pollinators is the main reproductive isolation between interfertile C. tibeticum and C. flavum, while C. tibeticum and C. smithii tend to hybridize naturally.     

Ecological barriers to early colony establishment in three coexisting acacia-ant species in Kenya

In black cotton uplands in East Africa, four symbiotic acacia-ant species compete for possession of a single swollen thorn tree species, Acacia drepanolobium, and yet coexist at fine spatial scales. Three of the four ant species produce independent foundress queens that establish colonies claustrally within swollen thorns, most often on small saplings. We conducted surveys of such saplings at two sites in 2001 and 2004, and examined foundresses and incipient colonies within their swollen thorns to determine what factors influence their success. Competition among foundresses for nest initiation sites was intense, with an average of over one founding attempt per swollen thorn in all samples, and with living and dead queens significantly hyper-dispersed among available thorns. Combat with other foundresses was the most common cause of death among claustral queens, especially for Tetraponera penzigi. In interspecific battles for nest initiation sites, T. penzigi was dominant over Crematogaster nigriceps and C. mimosae, and C. nigriceps won over 80% of its contests with C. mimosae foundresses. For singleton foundresses, brood parasitism by the braconid wasp Trigastrotheca laikipiensis typically results in the death of the entire ant brood. Host queens defend parasite larvae, pupae and eclosed adults, apparently unable to distinguish the wasps from legitimate offspring. Rates of brood parasitism were as high as 15–20% for incipient colonies of both Crematogaster species, but were extremely low for T. nigriceps in all samples. Although T. penzigi and C. nigriceps foundresses are always solitary, approximately 18% of claustral C. mimosae colonies contain cooperating pleometrotic queens. For unparasitized, claustral C. mimosae colonies, brood production per queen did not differ between solitary and cooperating foundresses. However, the per-capita risks associated with parastitism were reduced for pleometrotic queens. Received 8 March 2005; revised 23 May 2005; accepted 3 June 2005.     

Queen fecundity and reproductive skew in the termite Nasutitermes corniger

A major goal of studies on social animals is to understand variation in reproduction within and between groups. We used hierarchical regressions to analyze oviposition rates in the neotropical termite Nasutitermes corniger, a species with both monogynous and polygynous colonies. Queen fecundity was a non-linear, saturating function of queen weight. Greater queen weight was associated with larger nest size and with lower numbers of queens per nest, suggesting competition among queens for resources acquired by the colony. The collective egglaying rate of pairs of queens exceeded that of single queens, but further increases in queen number did not raise total fecundity. Skew in oviposition rates, as quantified by Morisita’s index I _δ, averaged 1.2, indicating inequalities in reproductive rates that are only moderately greater than expected for random apportionment. The leveling off of oviposition with increasing queen weight suggests that it is costly for individual females to produce eggs at high rates, which could favor tolerance of reproduction by other females, reducing reproductive skew. We hypothesize that the incentive to tolerate reproduction by other females is especially pronounced for heavier queens, because these queens are close to the limit of their own reproductive capacity. Consistent with this hypothesis, skew in oviposition rates was inversely related to the mean weight of queens within a nest. Received 8 March 2007; revised 17 September 2007; accepted 3 October 2007.     

Do army ant queens re-mate later in life?

Queens of eusocial Hymenoptera are inseminated only during a brief period before they start to lay eggs. This has probably been kin-selected because repeated insemination of old queens would normally be against the inclusive fitness interest of their daughter workers. Army ants have been considered to be the only possible exception to this rule due to their idiosyncratic life-history. We studied two distantly related species of army ants, the African Dorylus (Anomma) molestus and the Neotropical Eciton burchellii and present data from microsatellite genotyping, behavioural observations and sperm counts.We also describe the copulation behaviour of African army ants for the first time. Our results strongly suggest that, contradictory to earlier contentions, army ant queens do not mate repeatedly throughout their life and thus do not constitute an exception among the eusocial Hymenoptera in this respect. Sperm counts for males and queens of both species show that army ant queens have to mate with several males to become fully inseminated. However, sperm limitation by queens is unlikely to have been the prime reason for the evolution of high queen-mating frequencies in this group. Received 5 July 2006; revised 26 September 2006; accepted 11 October 2006.     

Host colony usurpation by the queen of the Japanese pirate ant, Polyergus samurai (hymenoptera: formicidae)

Colony usurpations by newly mated queens of Polyergus samurai were observed under artificial conditions. Newly mated queens of P. samurai were introduced into three kinds of Formica japonica host colonies: queenright, queenless (artificially orphaned), and workerless (only a queen remaining) colonies. In the queenright condition, the P. samurai queen intruded into the host nest and killed the host queen, and was subsequently adopted by the host workers. In all queenright and queenless host colonies, seven of 13 queens of P. samurai succeeded in colony usurpation, although the starting time of grooming, a nestmate behavior, by host workers in the queenright condition occurred earlier than in the queenless condition. In workerless conditions, four of five P. samurai queens ignored the F. japonica queen. The results suggest that while host-queen killing is not necessary, it is important to win acceptance by host workers.     

A shift in colony founding behaviour in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2

Summary. A shift in colony founding behaviour from single queen (haplometrosis) to multiple queens (pleometrosis) was observed locally in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2, which is associated with Macaranga trees in Borneo. In addition, about a quarter of all mature colonies (27 of 95 trees examined) were found to be multiple queen colonies. They arose either directly from pleometrotic founding colonies or secondarily by adoption of additional queens. Using microsatellite markers, we showed that queens in colonies founded through pleometrosis are unrelated and each queen participates in producing worker offspring, albeit with significant skew in a third of the colonies. In mature polygynous colonies, all resident queens contributed to the production of workers and sexual offspring. Relatedness of queens in mature polygynous colonies was not significantly higher than in foundress associations. We hypothesize that increased nest site limitation in this specific interaction trigger the observed shift in colony founding behaviour. Crematogaster msp. 2 inhabits the light demanding pioneer plant species Macaranga pearsonii that is typical for early successional stages of secondary forests. Thus suitable host-plants for colonisation are abundant for only a short time in highly disturbed sites and become increasingly sparse when secondary forest matures.Received 6 September 2004; revised 29 November; accepted 10 December 2004.     

Morpho-functional comparison of the Dufour gland in the female castes of the Amazon ant <Emphasis Type="Italic">Polyergus rufescens</Emphasis> (Hymenoptera,Formicidae)

The Dufour gland is crucially involved in main aspects of the parasite habit of the slave-making ant Polyergus rufescens, i.e. slave-raids and host colony usurpation. Workers use chemicals from this gland as recruitment signals during raid organization, while newly-mated queens use its secretion to appease residents during host nest invasion. Here, we report a comparison of the general morphology and fine structure of the Dufour gland in the female castes of P. rufescens: queens, ergatogynes (intermediate forms), and workers. The analysis clearly shows the link between gland structure and its behavioural role in queens and workers. In particular, queens present a hypertrophied gland with an extended lumen and a thin epithelium no more active in secretory function. This is consistent with the fact that usurper queens use the Dufour gland contents only during the short phase of host nest penetration. Contrary to adult queens, the cytoplasmic organization of the Dufour gland epithelium of raiders is typical for a tissue with secretory activity (abundance of mitochondria, free ribosomes, strands of smooth endoplasmic reticulum and a Golgi apparatus). This is consistent with the continuous raiding activity performed by workers throughout their adult life. The biology of ergatogynes is still an enigmatic matter. Their Dufour gland is intermediate in shape and size between that of queens and workers. It presents a fairly thick epithelium with features that are typical of a quite active secretory tissue.     

Polyandry in two South American harvester ants

Although monandry (single mating) is the ancestral state in social hymenopteran insects, effective mating frequencies greater than 2 have been confirmed for a fair amount of ant species: Cataglyphis cursor, the leaf-cutters of the genera Atta and Acromyrmex, army ants of the genera Eciton, Dorylus, Aenictus and Neivamyrmex, and some North American seed harvester species of the genus Pogonomyrmex. This last genus spreads throughout open arid habitats from Patagonia to southwestern Canada. Whereas some North American Pogonomyrmex species are thoroughly studied, we know much less about these ants in South America. The objective of this study was to estimate the effective mating frequency of Pogonomyrmex inermis and P. pronotalis, two Pogonomyrmex sensu stricto species from the central Monte desert of Argentina. A total of 477 P. pronotalis workers from 24 colonies and 402 P. inermis workers from 20 colonies were analyzed using six and four highly polymorphic microsatellites, respectively. The multilocus analysis revealed that all colonies were monogynous and all queens multiply-mated. The effective mating frequency was 8.75 and 6.52 for queens of P. pronotalis and P. inermis, respectively; those values increased up to 15.66 and 9.78, respectively, when corrected for sampling errors. This is the first demonstration that queens in at least some members of the South American Pogonomyrmex sensu stricto are strictly polyandrous, with mating numbers per queen at least as high as those previously found for North American species. We suggest that multiple mating probably arose early in the evolution of the genus Pogonomyrmex and may be the basis of its ecological success and wide distribution. Received 11 October 2006; revised 10 August 2007 and 19 November 2007; accepted 21 November 2007.     

A polygynous nest ofVespula pensylvanica from California with a discussion of possible factors influencing the evolution of polygyny inVespula

Summary A thriving, polygynous, and probably overwintered colony of the western yellowjacket,Vespula pensylvanica, was collected on 2 November 1994 in Riverside, southern California, and examined in detail. The colony had 14 combs, of combined area 1.30 m² containing 55,704 small and 10,266 large cells. There were 17 functional, physogastric queens, 70 newly emerged non-reproductive queens, 7300 adult workers, 685 adult males, and c. 17,600 capped cells containing pupae or fully-fed larvae. Dissections of 200 workers showed that none had well-developed ovaries. Hypotheses for the rarity of polygyny inVespula are put forward and evaluated.     

Potential cause of lethality of an allele implicated in social evolution in fire ants

The gene Gp-9 is believed to have a major effect on colony social organization in fire ants, with the presence of b-like alleles in a colony associated with multiple-queen (polygyne) organization. Queens and workers of polygyne Solenopsis invicta homozygous for the b-like allele designated b suffer reduced viability compared to other genotypes, and bb queens do not survive to become egg-layers. Thus, the b allele effectively acts as a recessive lethal. This allele differs from the remaining b-like alleles (designated b′), as well as all other Gp-9 alleles, by encoding a lysine at position 151 in the protein product, suggesting that this substitution is responsible for its deleterious effects. We tested this hypothesis by comparing frequencies of b′b′ and bb homozygotes, first in queens of Solenopsis richteri and S. invicta, then in S. invicta workers from populations polymorphic for the two b-like alleles. We found that almost 20% of S. richteri queens were b′b′ homozygotes, compared to the virtual absence of bb homozygotes among S. invicta queens, and that 5–18% of S. invicta workers bore genotype b′b′, compared to the apparent lack of bb workers in the same populations. While we cannot entirely rule out involvement of other genes in complete gametic disequilibrium with Gp-9, our data are consistent with the hypothesis that the Lys¹⁵¹ residue in GP-9 protein confers the deleterious effects of the b allele in homozygous condition, possibly by impairing the protein’s function through interference with ligand binding/release or hindrance of dimer formation.     

Male parentage and queen mating frequency in the bumblebee <Emphasis Type="Italic">Bombus ignitus</Emphasis> (Hymenoptera: bombinae)

Kin selection theory predicts conflict between queens and workers in the social insect colony with respect to male production. This conflict arises from the haplodiploid system of sex determination in Hymenoptera that creates relatedness asymmetries in which workers are more closely related to the sons of other workers than to those of the queen. In annual hymenopteran societies that are headed by a single queen, the mating frequency of the queen is the only factor that affects the colony kin structure. Therefore, we examined the mating structure of queens and the parentage of males in a monogynous bumblebee, Bombus ignitus, using DNA microsatellites. In the seven colonies that were studied, B. ignitus queens mated once, thereby leading to the prediction of conflict between the queen and workers regarding male production. In each of the five queen-right colonies, the majority of the males (95%) were produced by the colony’s queen. In contrast, workers produced approximately 47% of all the males in two queenless colonies. These results suggest that male production in B. ignitus is a conflict between queen and workers.     

Scaling of body weight and fat content in fungus-gardening ant queens: does this explain why leaf-cutting ants found claustrally?

Offspring traits are among the most important life history traits, yet we lack an adequate understanding of their role in social insect life history evolution. Colony founding in the fungus-gardening ants (Tribe Attini) is different from most other ant species because the queens forage during the founding phase. Queens of the most derived genus, Atta, are the only attines that exhibit the more typical claustral founding, where the queens seal themselves in a below-ground chamber and produce their first generation of workers with only body fat reserves. Here I report the dry weights, fat content and energetic value of newly mated queens of ten attine species. Published phylogenies were used to make inferences on the evolutionary transitions in this clade. It appears that the evolution of fungus-gardening was associated with the manufacture of smaller, leaner queens as basal taxa are characterized by small bodies that contain relatively less fat than derived taxa. Moreover, there appears to be an allometric function between fat, energetic content and dry weight, which means that for fatter and claustral queens to develop, they also must become larger.     

Contents of Dufour glands in some formicine ants: queens and workers of Camponotus aethiops and a re-examination of Lasius fuliginosus

The Dufour gland secretions of both virgin queens and workers of Camponotus aethiops are similar and consist of straight chain hydrocarbons ranging from C₁₀–C₁₅ with C₁₁ the major compound. The difference between the two castes is that C₁₅ appears only as a trace in queens, and the total amount of secretion is smaller in queens than in workers.In Lasius fuliginosus, the Dufour gland secretion contains a series of straight chain hydrocarbons (C₁₀–C₁₇) with undecane the major compound, and a series of 2-alkanones ranging from C₁₃ to C₁₉.

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Résumé Les sécrétions des glandes de Dufour sont toutes semblables et comprennent, chez les reines et les ouvrières de C. aethiops, une chaîne linéaire d'hydrocarbures de C₁₀ à C₁₅, avec C₁₁ comme constituant principal. Les différences entre les castes se traduisent chez la reine, par une teneur totale en sécrétions plus faible et l'existence de C₁₅ uniquement sous forme de traces.Chez L. fuliginosus, la sécrétion de la glande de Dufour comprend une série de chaînes linéaires d'hydrocarbures (C₁₀–C₁₇) avec l'undécane comme constituant principal, et une série de 2-alkanones allant de C₁₃ à C₁₉.

     

Queen polymorphism in the North American harvester ant,Ephebomyrmex imberbiculus

Summary In the North American harvester antEphebomyrmex imberbiculus, in addition to dealate queens, wingless female reproductives occur that have greatly reduced ocelli and thoracic sutures (intermorphic queens). Both queen types are equivalent in function, and do not differ in ovarian morphology. Colonies may contain several inseminated and egg-laying intermorphic queens. We discuss queen polymorphism in respect to the biology of this desert-dwelling species.     

Kin structure and colony male reproduction in the hornet<Emphasis Type="Italic"> Vespa crabro</Emphasis> (Hymenoptera: Vespidae)

We estimated queen mating frequency, genetic relatedness among workers, and worker reproduction in Vespa crabro flavofasciata using microsatellite DNA markers. Of 20 colonies examined, 15 contained queens inseminated by a single male, 3 colonies contained queens inseminated by two males, and 2 colonies contained queens inseminated by three males. The genetic relatedness among workers was estimated to be 0.73±0.003 (mean±SE). For this high relatedness, kin selection theory predicts a potential conflict between queens and workers over male production. To verify whether males are derived from queens or workers, 260 males from 13 colonies were genotyped at four microsatellite loci. We found that all of the males were derived from the queens. This finding was further supported by the fact that only 33 of 2,990 workers dissected had developed ovaries. These workers belonged to 2 of the 20 colonies. There was no relationship between queen mating frequency and worker reproduction, and no workers produced male offspring in any of the colonies. These results suggest that male production dominated by queens in V. crabro flavofasciata is possibly due to worker policing.     

Number of queens in founding associations of the ponerine ant Pachycondyla villosa

In the ant Pachycondyla villosa, new colonies are usually started cooperatively by two or more young queens who establish a dominance order with a division of labour. Co-founding can lead to primary polygyny, where queens stay together after workers have emerged. Here we show that two queens associations are the most common (47%) and also the most stable in the field. When offered additional nest sites in the laboratory, two-queen associations did not split, whereas larger associations did so. We also show that solitary foundresses always accepted experimentally introduced alien queens, while these were attacked and sometimes killed in queen associations. The removal of dominant alpha queens from three-queen associations resulted in beta queens obtaining the dominant role and sometimes the destruction of the existing eggs. It appears that two queens suffice for a successful association and that pleometrosis is favoured by ecological constrains, such as nest-site limitation. Received 28 February 2005; revised 20 April 2005; accepted 22 April 2005.     

The reproductive phenology of an Amazonian ant species reflects the seasonal availability of its nest sites

In saturated tropical ant assemblages, reproductive success depends on queens locating and competing for scarce nest sites. Little is known about how this process shapes the life histories of tropical ants. Here I investigate the relationship between nest site availability and an important life history trait, reproductive phenology, in the common Amazonian ant species Allomerus octoarticulatus. A. octoarticulatus is a plant-ant that nests in the hollow, swollen stem domatia on Cordia nodosa. I provide evidence that nest sites are limiting for A. octoarticulatus. Most queens produced by A. octoarticulatus colonies died before locating suitable host plants, and most queens that located hosts died before founding colonies, probably from intraspecific competition among queens for control of host plants. I further show that the reproductive phenology of A. octoarticulatus closely matches the seasonal availability of its nest sites, domatia-bearing C. nodosa saplings. Both the production and flight of A. octoarticulatus reproductives, and the number of C. nodosa saplings available for colonization by ants, peaked from March to May. There was correlative evidence that A. octoarticulatus colonies use temperature as a cue to synchronize their reproduction to the availability of C. nodosa saplings: both the production of reproductives by ant colonies and the number of C. nodosa saplings available for colonization were correlated with temperature, and not with rainfall. All of these results suggest that nest site limitation constrains the reproductive phenology of A. octoarticulatus.     

Yolk protein in the pharaoh's ant: Influence of larvae and workers on vitellogenin and vitellin content in queens

Summary Vitellin from the pharaoh's ant,Monomorium pharaonis (L.), was found to contain a single apoprotein with aM _r of 198.3 kDa. The protein is a glycoprotein exposing mannose containing carbohydrate groups.Antibodies to pharaoh's ant vitellin (v _t), raised in rabbits, were used to determine the head-, thorax-, and abdominal contents of vitellogenin and vitellin (v _g+v_t) in queens in relation to the presence or absence of larvae and workers using an ELISA test. Thev _g+v_t contents were also compared to the egg-laying rate and the weight of the queens.The results confirm the existence of a positive correlation betweenv _g+v_t contents in the queens and their access to larvae, probably related to the queens' preferential feeding on larval secretions. In queens without larvae the abdominalv _g+v_t contents declined in concordance with a low oviposition rate of 6–8 eggs/day. In spite of cessation of egg-laying within 24 hours after removal of both larvae and workers, the queens maintained basal contents ofv _g+vt. This may indicate that the presence of larvae is not only essential for the nutrition of the queens, but also for the uptake of vitellogenin in the growing oocytes. This additional stimultive factor may be based on the queens' response to primer pheromones liberated by the larvae. v _g+v_t could not be demonstrated in workers or larvae with the ELISA test. If anyv _g+vt is present in larvae and workers the amount is lower than the detection limit (1–2 ng/individual). This seems to rule out the possibility of transfer of proteins of this kind to the queens.     

Ant colonization of Maieta guianensis seedlings,an Amazon ant-plant

The ants Pheidole minutula and Crematogaster sp. are obligate inhabitants of the ant-plant Maieta guianensis. They nest and reproduce exclusively in this and a few other Amazon melastome ant-plants. Experimental transplants of uncolonized M. guianensis seedlings to sites at different distances from established colonies of these two ant species, which are sources of founding queens, have shown that distance is an important factor affecting seedling colonization by ants. The proportion of colonized seedlings and the average number of colonizations per seedling, both by Crematogaster sp. and P. minutula, decreased as distance from established colonies increased. Seedling colonization was also affected by rainfall and fewer seedlings were colonized during the dry season, especially by P. minutula, than during the rainy season. P. minutula queens usually cooperate with each other during colony foundation, a behaviour not observed among founding queens of Crematogaster sp. Competition between these two ant species for host-plants appears to be strong as 63.6% of the seedlings colonized by Crematogaster sp. were also colonized by P. minutula during a 15-month observational period. However, there was generally an interval of a few months between colonizations, possibly giving the first species to colonize the plant a better chance of domination on this plant.     

Ecology of spiders inhabiting abandoned mammal burrows in South African savanna

Summary We marked the sites chosen by 338 foundress queens of two desert ant species (Veromessor pergandei and Myrmecocystus flaviceps) and monitored changes in the spacing of both species and the foraging activity at V. pergandei young nests. Although the long established colonies of both species tend intraspecifically toward regular dispersion, queens of both species were intraspecifically clumped. After 3 months, when the first workers emerged, the young colonies (reduced to a total of 42 colonies) were randomly spaced intraspecifically. We also followed the spatial patter of queens with respect to established colonies of both species. Queens founded nests away from the nests of all established colonies on the site. After three months, the young colonies were dispersed away from conspecifics only. During June through August 1986, we censused the number of foragers at the surviving V. pergandei nests. Young colonies that were more active also tended to be far from established conspecifics in July and August. There was no correlation of forating activity with distance to heterospecific established colonies in any month. These results indicate that established conspecifics may reduce the survivorship of young ant colonies.