Hydrocarbon site of synthesis and circulation in the desert ant Cataglyphis niger

Chemical analyses revealed that in Cataglyphis niger both the hemolymph and the crop contain the same hydrocarbons that are found in the postpharyngeal gland (PPG). On the cuticle, on the other hand, alkanes, and in particular nonacosane, were more abundant than in the PPG. Studies of their biosynthesis in vivo, using intact ants, revealed the presence of newly synthesized hydrocarbons in both the PPG and the crop. In decapitated ants (in the absence of the PPG), however, the crop did not contain any newly synthesized hydrocarbons, indicating the PPG as the major source of crop hydrocarbons. The fat body, as demonstrated by in vitro studies, is the major tissue that biosynthesizes hydrocarbons. The PPG failed to do so, but showed good de novo biosynthesis of other lipid constituents. The large amount of hydrocarbons in the crop suggests that the alimentary canal may serve as an outlet for the overflow of PPG hydrocarbons, or as a route for the directed clearance of hydrocarbons from the PPG.These results confirm and enlarge the model proposed for hydrocarbon circulation in C. niger. They are synthesized by the fat body, released to the hemolymph and transported to the cuticle and the PPG. The PPG hydrocarbons are applied to the cuticle by self-grooming, but can also be cleared via the alimentary canal. Partial emptying of the PPG may facilitate the admixing of recognition cues that the ant may acquire from nestmates by trophallaxis. The reason for the dissimilarity in hydrocarbon composition between the PPG and the cuticle is not yet clear; it may be due to secretions from additional glands, or reflect deviant hydrocarbon transport mechanisms between the PPG and the cuticle.     

Discrimination of inclined path segments by the desert ant Cataglyphis fortis

Desert ants (Cataglyphis fortis) navigate by means of path integration, and perform accurately even in undulating terrain. They are able to correctly calculate the ground distance between nest and feeder even if their foraging excursion leads them over corrugated surfaces. To compute the respective ground projection when walking over an inclined surface, ants must measure its slope with sufficient accuracy—but how they do so is still not understood. Using a new behavioural assay that included a negative reinforcement, we investigated how well different slopes are discriminated by the ants. Ants were trained to visit an elevated feeder, via a ramp of fixed inclination (five training inclinations were used: 0°, 15°, 30°, 45°, 60°). The ants discriminated a steeper test slope that differed from the training slope by 12.5°. This discrimination performance was found to be constant for training slopes between 0° and 45°. Ants trained on a 60° slope, however, did not discriminate all steeper slopes, up to a vertical ascent, from the 60° inclination. The consequences of this discrimination accuracy for errors in the path integration process are discussed.     

Structural and chemical ontogeny of the postpharyngeal gland in the desert ant Cataglyphis niger

Abstract. The postpharyngeal gland of Cataglyphis niger (André, 1881) workers is characterized, at the ultrastructural level, by a well-developed smooth endoplasmic reticulum, Golgi apparatus, and numerous mitochondria and lamellar inclusions suggesting an involvement in lipid metabolism. In addition, the microvillar differentiation of the apical membrane and basal invaginations of the cell imply a transportation process.
The gland shows a clear structural as well as chemical age-dependent development. Epithelial thickness increases with age, reaching its maximum within the first week after emergence. Concurrently there is a progressive development of microvilli and appearance of the lamellar inclusions. The gland's secretion consists mainly of hydrocarbons, with a predominance of monomethyl and dimethyl alkanes. Congruency was found between the hydrocarbon composition of glandular exudates and those of the epicuticular washes. An age-dependent increase in the total amount of hydrocarbons was found to correlate with the ultrastructural development and gross morphology (thickness of epicuticular lining) of the gland.     

Worker demography and behavior in a supercolonial ant colony: The case of the desert ant Cataglyphis niger

Insect societies headed by multiple queens (polygyny) raise evolutionary questions, such as how does genetic heterogeneity among colony members affect in-nest interactions; or, are all queens equally reproductive or equally treated by workers? Answering such questions requires intensive and continuous observations of in-nest behavior. Here, we addressed these questions in the polygyne supercolonial ant, Cataglyphis niger, using a barcoding system that enables the tracking of individual interactions, together with polymorphic DNA microsatellite markers that indicate the matriline and patriline of all individuals. Our findings that both queens and workers have low interrelatedness corroborate earlier reports regarding the supercolony structure of C. niger. Ovary inspection and worker genotyping revealed that all the queens contribute similarly to nest demography. Tracking positions of individual workers through time revealed that only a small proportion of them are constantly engaged in tending the queens and can be considered as retinue workers. However, genotyping these workers and the attended queens revealed no relationship to genetic relatedness, again typical of a true polygyne and supercolonial species. Unlike invasive supercolonial species, C. niger is native to Israel, enabling us to address questions regarding the driving forces, other than kin selection, that stabilize this society.     

Hierarchical analysis of population genetic structure in the monogynous ant Cataglyphis cursor using microsatellite and mitochondrial DNA markers

Despite having winged queens, female dispersal in the monogynous ant Cataglyphis cursor is likely to be restricted because colonies reproduce by fission. We investigated the pattern of population genetic structure of this species using eight microsatellite markers and a mitochondrial DNA (mtDNA) sequence, in order to examine the extent of female and nuclear gene flow in two types of habitat. Sampling was carried out at a large spatial scale (16 sites from 2.5 to 120 km apart) as well as at a fine spatial scale (two 4.5-km transects, one in each habitat type). The strong spatial clustering of mtDNA observed at the fine spatial scale strongly supported a restricted effective female dispersal. In agreement, patterns of the mtDNA haplotypes observed at large and fine spatial scales suggested that new sites are colonized by nearby sites. Isolation by distance and significant nuclear genetic structure have been detected at all the spatial scales investigated. The level of local genetic differentiation for mitochondrial marker was 15 times higher than for the nuclear markers, suggesting differences in dispersal pattern between the two sexes. However, male gene flow was not sufficient to prevent significant nuclear genetic differentiation even at short distances (500 m). Isolation-by-distance patterns differed between the two habitat types, with a linear decrease of genetic similarities with distance observed only in the more continuous of the two habitats. Finally, despite these low dispersal capacities and the potential use of parthenogenesis to produce new queens, no signs of reduction of nuclear genetic diversity was detected in C. cursor populations.     

Visual experience and age affect synaptic organization in the mushroom bodies of the desert ant Cataglyphis fortis

Desert ants of the genus Cataglyphis undergo an age‐related polyethism from interior workers involved in brood care and food processing to short‐lived outdoor foragers with remarkable visual navigation capabilities. The quick transition from dark to light suggests that visual centers in the ant's brain express a high degree of plasticity. To investigate structural synaptic plasticity in the mushroom bodies (MBs)—sensory integration centers supposed to be involved in learning and memory—we immunolabeled and quantified pre‐ and postsynaptic profiles of synaptic complexes (microglomeruli, MG) in the visual (collar) and olfactory (lip) input regions of the MB calyx. The results show that a volume increase of the MB calyx during behavioral transition is associated with a decrease in MG numbers in the collar and, less pronounced, in the lip. Analysis of tubulin‐positive profiles indicates that presynaptic pruning of projection neurons and dendritic expansion in intrinsic Kenyon cells are involved. Light‐exposure of dark‐reared ants of different age classes revealed similar effects. The results indicate that this structural synaptic plasticity in the MB calyx is primarily driven by visual experience rather than by an internal program. This is supported by the fact that dark‐reared ants age‐matched to foragers had MG numbers comparable to those of interior workers. Ants aged artificially for up to 1 year expressed a similar plasticity. These results suggest that the high degree of neuronal plasticity in visual input regions of the MB calyx may be an important factor related to behavior transitions associated with division of labor. © 2010 Wiley Periodicals, Inc. Develop Neurobiol 70: 408–423, 2010     

Ventilation and respiratory metabolism in the thermophilic desert ant,Cataglyphis bicolor (Hymenoptera,Formicidae)

The discontinuous ventilation cycle of the Saharan desert ant Cataglyphis bicolor was studied over the range 15–40°C, corresponding to a >2-fold increase in the rate of CO₂ output and hence metabolic rate (Q ₁₀=2.1). Over this range, metabolic rate modulated only ventilation frequency; the volume of CO₂ emitted per ventilation remained constant. The closed-spiracle phase accounted for a small, constant proportion (ca. 14%) of total CO₂ output. In the flutter phase, the rate of CO₂ output increased at a greater than exponential rate from 29% of total CO₂ output at 15°C to 52% at 40°C. CO₂ output rate in the ventilation phase increased, and its duration decreased, exponentially with temperature. Relative to total duration of discontinuous ventilation cycle, the length of each phase was constant over the entire range of metabolic rates measured. These data are the first thorough characterization of the effect of changing metabolic rate on all phases of the discontinuous ventilation cycle of an adult insect. Clearly, C. bicolor maximizes ventilation-phase emission volumes and enhances the contribution of the flutter phase to total CO₂ release relative to other ants for which comparable data are available, and does so in ways that may reduce respiratory water loss rates.Abbreviations BM body mass - C-phase closed-spiracle phase - cVCO₂ rate of carbon dioxyde leakage during the C phase - DVC discontinuous ventilation cycle - F-phase fluttering-spiracle phase - MR metabolic rate - Q ₁₀ factorial increase in MR with 10°C increase in temperature - RQ respiratory quotient - SMR standard metabolic rate - T body temperature (°C) - VCO₂ rate of carbon dioxide output - V-phase ventilation phase - vVCO₂ rate of CO₂ emission during the V-phase - fVCO₂ rate of CO₂ emission during the F-phase - VO₂ rate of oxygen consumption     

Visual experience affects both behavioral and neuronal aspects in the individual life history of the desert ant Cataglyphis fortis

The individual life history of the desert ant Cataglyphis fortis is characterized by a fast transition from interior tasks to mainly visually guided foraging. Previous studies revealed a remarkable structural synaptic plasticity in visual and olfactory input regions within the mushroom bodies of the ants' brain centers involved in learning and memory. Reorganization of synaptic complexes (microglomeruli) was shown to be triggered by sensory exposure rather than an internal program. Using video analyses at the natural nest site and activity recordings after artificial light treatments we investigated whether the ants get exposed to light before onset of foraging and whether this changes the ants' activity levels. We asked whether synaptic reorganization occurs in a similar time window by immunolabeling and quantification of pre- and postsynaptic compartments of visual and olfactory microglomeruli after periods of light-exposure. Ants reverted back to dark nest conditions were used to investigate whether synaptic reorganization is reversible. The behavior analyses revealed that late-interior ants (diggers) are exposed to light and perform exploration runs up to 2 days before they start foraging. This corresponds well with the result that artificial light treatment over more than 2-3 days significantly increased the ants' locomotor activities. At the neuronal level, visual exposure of more than 1 day was necessary to trigger reorganization of microglomeruli, and light-induced changes were only partly reversible in the dark. We conclude that visual preexposure is an important and flexible means to prepare the ants' visual pathway for orientation capabilities essential during foraging.     

Social hybridogenesis in the clonal ant Cataglyphis hispanica

With a few rare exceptions, the vast majority of animals reproduce sexually. Some species have, however, evolved alternative modes of reproduction by shifting from classical bisexuality to unorthodox reproductive systems, like parthenogenesis, gynogenesis, or hybridogenesis. Under hybridogenesis, both the maternal and paternal genomes are expressed in somatic tissues, whereas the germline is purely maternal. Recently, a form of hybridogenesis at the level of the society has been reported in some ants, where purebred females develop into reproductive queens and interlineage hybrids into sterile workers. Here, we report a unique case of social hybridogenesis in the desert ant Cataglyphis hispanica. Workers are produced exclusively from interbreeding between two distinct genetic lineages, whereas male and female sexuals are produced by asexual reproduction through parthenogenesis. As a consequence, all workers are pure hybridogens, and only maternal genes are perpetuated from one generation to the next. Thus, queens of C. hispanica use sexual reproduction for colony growth, whereas they reproduce asexually through parthenogenesis for germline production.     

Multiple mating and supercoloniality in Cataglyphis desert ants

In social organisms, the breeding system corresponds to the number of breeders in a group, their genetic relationships, and the distribution of reproduction among them. Recent, genetically based studies suggest an amazing array of breeding system and reproductive strategies in desert ants of the genus Cataglyphis. Using highly polymorphic DNA microsatellites, we performed a detailed analysis of the breeding system and population genetic structure of two Cataglyphis species belonging to the same phylogenetic group: C. niger and C. savignyi. Our results show that both species present very different breeding systems. C. savignyi colonies are headed by a single queen and populations are multicolonial. Remarkably, queens show one of the highest mating frequency reported in ants (M_p = 9.25). Workers can reproduce by both arrhenotokous and thelytokous parthenogenesis. By contrast, colonies of C. niger are headed by several, multiply mated queens (M_p = 5.17), and they are organized in supercolonial populations made of numerous interconnected nests. Workers lay arrhenotokous eggs only. These results illustrate the high variability in the socio‐genetic organization that evolved in desert ants of the genus Cataglyphis. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 866–876.     

Mating frequency and genetic structure of the Argentine ant Linepithema humile

The nest and population genetic structures of the Argentine ant, Linepithema humile were investigated using eight microsatellite loci. Genotypes of the sperm from spermathecae of 87 queens were consistent with all queens being singly inseminated. The probability of a double mating remaining undetected was low (0.012) suggesting that no queens or only a very low proportion mate multiply. The relatedness between the queens and their mates was negative (R = -0.164 +/- 0.044) and significantly different to zero (P = 0.020). However, the high negative relatedness value was caused by a significant allele frequency difference between the sexes at a single locus (Lhum-28). When this locus was removed from the analyses, the relatedness was not significantly different from zero (R = 0.013 +/- 0.050, P = 0.812). Analysis of 10 nests revealed that the genetic differentiation among nests was weak (FST = 0.003) and not distinguishable from zero (P = 0.468). Similarly, the overall relatedness among nestmate females was not significantly different from zero (R = 0.007 +/- 0.018, P = 0.706). These results are consistent with the lack of distinct nest boundaries and the large number of queens per nest in the population studied. Although mating takes place inside the nest, the inbreeding coefficient was close to zero (F = 0.007 +/- 0.025, P = 0.786). Overall, these data indicate substantial local gene flow mediated by movement of reproductives among colonies.     

Breeding system, colony and population structure in the weaver ant Oecophylla smaragdina

Weaver ants ( Oecophylla smaragdina ) are dominant ants in open forests from India, Australia, China and Southeast Asia, whose leaf nests are held together with larval silk. The species, together with its sole congener O. longinoda , has been important in research on biological control, communication, territoriality and colony integration. Over most of the range, only one queen has been found per colony, but the occurrence of several queens per nest has been reported for the Australian Northern Territory. The number of males mating with each queen is little known. Here we report on the colony structure of O. smaragdina using published and new microsatellite markers. Worker genotype arrays reflect the occurrence of habitual polygyny (more than one queen per colony) in 18 colonies from Darwin, Northern Australia, with up to five queens inferred per colony. Monogyny (one queen per colony) with occasional polygyny was inferred for 14 colonies from Queensland, Australia, and 20 colonies from Java, Indonesia. Direct genotyping of the sperm carried by 77 Queensland queens and worker genotypic arrays of established colonies yielded similar results, indicating that less than half of the queens mate only once and some mate up to five times. Worker genotype arrays indicated that queens from Java and the Northern Territory also often mate with more than one male, but less often than those from Queensland. A strong isolation-by-distance effect was found for Queensland samples. The variation uncovered means that O. smaragdina is a more versatile study system than previously supposed.     

Local resource competition and sex ratio in the ant Cataglyphis cursor

The local resource competition (LRC) hypothesis predicts thatwherever philopatric offspring compete for resources with theirmothers, offspring sex ratios should be biased in favor of thedispersing sex. In ants, LRC is typically found in polygynous(multiple queen) species where foundation of new nests occursby budding, which results in a strong population structure anda male-biased population-wide sex ratio. However, under polygyny,the effect of LRC on sex allocation is often blurred by theeffect of lowered relatedness asymmetries among colony members.Moreover, environmental factors, such as the availability ofresources, have also been shown to deeply influence sex ratioin ants. We investigated sex allocation in the monogynous (singlequeen) ant Cataglyphis cursor, a species where colonies reproduceby budding and both male and female sexuals are produced throughparthenogenesis, so that between-colony variations in relatednessasymmetries should be reduced. Our results show that sex allocationin C. cursor is highly male biased both at the colony and populationlevels. Genetic analyses indicate a significant isolation-by-distancein the study population, consistent with limited dispersal offemales. As expected from asexual reproduction, only weak variationsin relatedness asymmetry of workers toward sexual offspringoccur across colonies, and they are not associated with colonysex ratio. Inconsistent with the predictions of the resourceavailability hypothesis, the male bias significantly increaseswith colony size, and investment in males, but not in females,is positively correlated with total investment in sexuals. Overall,our results are consistent with the predictions of the LRC hypothesisto account for sex ratio variation in this species.     

Path integration in desert ants, Cataglyphis: how to make a homing ant run away from home

Path integration is an ant's lifeline on any of its foraging journeys. It results in a homebound global vector that continually informs the animal about its position relative to its starting point. Here, we use a particular (repeated training and displacement) paradigm, in which homebound ants are made to follow a familiar landmark route repeatedly from the feeder to the nest, even after they have arrived at the nest. The results show that during the repeated landmark-guided home runs the ant's path integrator runs continually, so that the current state of the homebound vector increasingly exceeds the reference state. The dramatic result is that the homing ants run away from home. This finding implies that the ants do not rely on cartographic information about the locations of nest and feeder (e.g. that the nest is always south of the feeder), but just behave according to what the state of their egocentric path integrator tells them.     

Microvillar orientation in the photoreceptors of the ant Cataglyphis bicolor

Polarization sensitivity in arthropod photoreceptors is crucially dependent on the arrangement of the microvilli within the rhabdom. Here, we present an electron-microscopical study in which the degree of microvillar alignment and changes in the cross-sectional areas of the rhabdoms along their length were studied in the compound eye of the desert ant, Cataglyphis bicolor. Serial cross-sections through the retina were taken and the orientation of the microvilli was determined in the photoreceptors of individually identified ommatidia. The reconstructions of microvillar alignment were made in the three anatomically and functionally distinct regions of the Cataglyphis compound eye: the dorsal rim area (DRA), the dorsal area (DA), and the ventral area (VA). The following morphological findings are consistent with polarization sensitivities measured previously by intracellular recordings. (1) The microvilli of the DRA photoreceptors are aligned in parallel along the entire length of the cell from the distal tip of the rhabdom down to its proximal end, near the basement membrane. The microvilli of the retinular cells R1 and R5 are always parallel to each other and perfectly perpendicular, with only minor deviation, to the microvillar orientation of the remaining receptor cells. (2) In the DA and VA regions of the eye, the microvillar tufts of the small receptors R1, R3, R5, R7, and R9 change their direction repetitively every 1-4 7m for up to 90°. In contrast, the large receptor cells R2, R4, R6, and R8 maintain their microvillar orientation rigidly. (3) In the DRA ommatidia, the cross-sectional areas of the rhabdomeres do not change along the length of the rhabdom, but substantial changes occur in the DA and VA ommatidia.     

Investigation of the population genetic structure and mating system in the ant Pheidole pallidula

The origin of eusociality in haplo-diploid organisms such as Hymenoptera has been mostly explained by kin selection. However, several studies have uncovered decreased relatedness values within colonies, resulting primarily from multiple queen matings (polyandry) and/or from the presence of more than one functional queen (polygyny). Here, we report on the use of microsatellite data for the investigation of sociogenetic parameters, such as relatedness, and levels of polygyny and polyandry, in the ant Pheidole pallidula. We demonstrate, through analysis of mother-offspring combinations and the use of direct sperm typing, that each queen is inseminated by a single male. The inbreeding coefficient within colonies and the levels of relatedness between the queens and their mate are not significantly different from zero, indicating that matings occur between unrelated individuals. Analyses of worker genotypes demonstrate that 38% of the colonies are polygynous with 2-4 functional queens, and suggest the existence of reproductive skew, i.e. unequal respective contribution of queens to reproduction. Finally, our analyses indicate that colonies are genetically differentiated and form a population exhibiting significant isolation-by-distance, suggesting that some colonies originate through budding.     

Hybridogenesis through thelytokous parthenogenesis in two Cataglyphis desert ants

Hybridogenesis is a sexual reproductive system, whereby parents from different genetic origin hybridize. Both the maternal and paternal genomes are expressed in somatic tissues, but the paternal genome is systematically excluded from the germ line, which is therefore purely maternal. Recently, a unique case of hybridogenesis at a social level was reported in the desert ant Cataglyphis hispanica. All workers are sexually produced hybridogens, whereas sexual forms (new queens and males) are produced by queens through parthenogenesis. Thus, only maternal genes are perpetuated across generations. Here, we show that such an unusual reproductive strategy also evolved in two other species of Cataglyphis belonging to the same phylogenetic group, Cataglyphis velox and Cataglyphis mauritanica. In both species, queens mate exclusively with males originating from a different genetic lineage than their own to produce hybrid workers, while they use parthenogenesis to produce the male and female reproductive castes. In contrast to single‐queen colonies of C. hispanica, colonies of C. velox and C. mauritanica are headed by several queens. Most queens within colonies share the same multilocus genotype and never transmit their mates' alleles to the reproductive castes. Social hybridogenesis in the desert ants has direct consequences on the genetic variability of populations and on caste determination. We also discuss the maintenance of this reproductive strategy within the genus Cataglyphis.