The ontogeny of foragwehaviour in desert ants, Cataglyphis bicolor

Abstract. 1. Individually foraging desert ants, Cataglyphis bicolor , exhibit short foraging lives (half lifetime, i.e. half-time of the exponential decay function: 4.5 days), in which they perform 3.7 ± 1.9 foraging runs per day.
2. During their short lifetime foraging period the ants increase the duration of their foraging round trips (up to 40.0 ± 24.6 min per run), the maximal distance of individual foraging runs (up to 28.2 ± 4.1 m), and their foraging success, i.e. the ratio of successful runs to the total number of runs (up to 0.70).
3. The parameter that increases most dramatically during a forager's lifetime is direction fidelity, i.e. the tendency to remain faithful to a particular foraging direction.
4. A model based on some simple behavioural rules is used to describe the experimental findings that within an isotropic food environment individual ants develop spatial foraging idiosyncrasies, and do so at a rate that increases with the food densities they encounter.
5. Finally, it is argued that in functional terms direction fidelity is related to the navigational benefits resulting from exploiting familiar (route-based) landmark information, and hence reduces round-trip time and by this physiological stress and predatory risk.     

Fine structure of light- and dark-adapted eyes of desert ants,Cataglyphis bicolor (Formicidae,Hymenoptera)

Among ants, Cataglyphis bicolor shows the best performance in optical orientation. Its eye is of the apposition type with a fused rhabdom. Morphological studies on the general struture of the eye as well as the effect of light have been carried out with transmission and scanning electron microscopy. An ommatidium is composed of a dioptric apparatus, consisting of a cornea, corneal process and a crystalline cone, the sensory retinula, which is made up of eight retinula cells in the distal half and of an additional ninth one in the proximal half. The ommatidia are separated from each other by two primary pigment cells, which surround the crystalline cone and an average of 12 secondary pigment cells, which reach from cornea to the basement membrane. The eye of Cataglyphis bicolor possesses a light intensity dependent adaptation mechanism, which causes a radial and distal movement of the pigment granules within the retinula cells and a dilatation of cisternae of the ER along the rhabdom. Until now, no overall order in arrangement of retinula cells or direction of microvilli has been found from ommatidium to ommatidium. Such an order, however, must exist, either on the retina or the lamina level, since we have proven the ant's capacity for polarized light analysis.     

Age-dependent and task-related volume changes in the mushroom bodies of visually guided desert ants, Cataglyphis bicolor

Desert ants of the genus Cataglyphis are skillful long-distance navigators employing a variety of visual navigational tools such as skylight compasses and landmark guidance mechanisms. However, the time during which this navigational toolkit comes into play is extremely short, as the average lifetime of a Cataglyphis forager lasts for only about 6 days. Here we show, by using immunohistochemistry, confocal microscopy, and three-dimensional reconstruction software, that even during this short period of adult life, Cataglyphis exhibits a remarkable increase in the size of its mushroom bodies, especially of the visual input region, the collar, if compared to age-matched dark-reared animals. This task-related increase rides on a much smaller age-dependent increase of the size of the mushroom bodies. Due to the variation in body size exhibited by Cataglyphis workers we use allometric analyses throughout and show that small animals exhibit considerably larger task-related increases in the sizes of their mushroom bodies than larger animals do. It is as if there were an upper limit of mushroom body size required for accomplishing the ant's navigational tasks.     

Smells like home: Desert ants, Cataglyphis fortis, use olfactory landmarks to pinpoint the nest

Background

Although some mechanisms of habitat adaptation of conspecific populations have been recently elucidated, the evolution of female preference has rarely been addressed as a force driving habitat adaptation in natural settings. Habitat adaptation of fire salamanders (Salamandra salamandra), as found in Middle Europe (Germany), can be framed in an explicit phylogeographic framework that allows for the evolution of habitat adaptation between distinct populations to be traced. Typically, females of S. salamandra only deposit their larvae in small permanent streams. However, some populations of the western post-glacial recolonization lineage use small temporary ponds as larval habitats. Pond larvae display several habitat-specific adaptations that are absent in stream-adapted larvae. We conducted mate preference tests with females from three distinct German populations in order to determine the influence of habitat adaptation versus neutral genetic distance on female mate choice. Two populations that we tested belong to the western post-glacial recolonization group, but are adapted to either stream or pond habitats. The third population is adapted to streams but represents the eastern recolonization lineage.

Results

Despite large genetic distances with F_ST values around 0.5, the stream-adapted females preferred males from the same habitat type regardless of genetic distance. Conversely, pond-adapted females did not prefer males from their own population when compared to stream-adapted individuals of either lineage.

Conclusion

A comparative analysis of our data showed that habitat adaptation rather than neutral genetic distance correlates with female preference in these salamanders, and that habitat-dependent female preference of a specific pond-reproducing population may have been lost during adaptation to the novel environmental conditions of ponds.     

Cataglyphis desert ants improve their mobility by raising the gaster

We analyze theoretically the moment of inertia of the desert ant Cataglyphis (C. bicolor and C. fortis) around a vertical axis through its own center of mass when the animal raises its gaster to a vertical position. Compared to the value when the gaster is horizontal, the moment of inertia is reduced to one half; this implies that when increasing its angular acceleration the ant need apply only half the level of torque when the gaster is raised, compared to when the gaster is lowered. As an example, we analyze the cases of an ant running on circular and sinusoidal paths. In both cases, the ant must apply a sideways thrust, anti-roll and anti-pitch torques to avoid toppling, and, on the circular path when accelerating and throughout the sinusoidal trajectory, a torque to enable turning as the path curves. When the ant is accelerating in a very tight circle or running on a very narrow sinusoidal path, in which the amplitude of the sinusoid is less than the length of the ant's body, the forces required for the turning torque can equal and exceed those required for the sideways thrust, and can be reduced significantly by the ant raising the gaster, whereas the foot-thrust for the anti-roll and anti-pitch torques rises only modestly when the gaster is up. This suggests that there may be an evolutionary advantage for employing the gaster-raising mode of locomotion, since this habit will allow desert ants to use lower forces and less energy, and perhaps run faster on more tortuous paths.     

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.     

Age‐dependent and task‐related volume changes in the mushroom bodies of visually guided desert ants,Cataglyphis bicolor

Desert ants of the genus Cataglyphis are skillful long‐distance navigators employing a variety of visual navigational tools such as skylight compasses and landmark guidance mechanisms. However, the time during which this navigational toolkit comes into play is extremely short, as the average lifetime of a Cataglyphis forager lasts for only about 6 days. Here we show, by using immunohistochemistry, confocal microscopy, and three‐dimensional reconstruction software, that even during this short period of adult life, Cataglyphis exhibits a remarkable increase in the size of its mushroom bodies, especially of the visual input region, the collar, if compared to age‐matched dark‐reared animals. This task‐related increase rides on a much smaller age‐dependent increase of the size of the mushroom bodies. Due to the variation in body size exhibited by Cataglyphis workers we use allometric analyses throughout and show that small animals exhibit considerably larger task‐related increases in the sizes of their mushroom bodies than larger animals do. It is as if there were an upper limit of mushroom body size required for accomplishing the ant's navigational tasks. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

Golgi studies of the first optic ganglion of the ant,Cataglyphis bicolor

The neurons of the first optic ganglion (the lamina) in the desert ant, Cataglyphis bicolor, have been studied with the light microscope after Golgi silver impregnation. The different types of retinal and laminal fibres and their configuration are compared with the results obtained in the bee. The first synaptic region in the visual system of the ant lies proximally to the fenestrated layer below the basement membrane and the layer containing the monopolar cell bodies. The synaptic region can be separated into three morphologically different zones: (1) The most distal layer where the short visual fibres end at two different levels. The short visual fibres and some laminal fibres (monopolar cell fibres) also show lateral elements in this region. (2) The second layer appears almost free of branches of retinal and laminal fibres. (3) The most proximal layer, which has a characteristically dense horizontal structure resulting from the lateral elements of long visual, centrifugal, monopolar and tangential fibres. Nine cell axons arising from each ommatidium leave the retina. Six of these are short visual fibres and end at two different levels in the lamina. Three different types of short visual fibres can be distinguished by their different terminal depths and lateral branching pattern. The remaining three fibres, the long visual fibres, terminate in the medulla. They can be distinguished from each other by their lateral elements in the lamina neuropile. The five morphologically different laminal fibre types (axons of the monopolar cells in the lamina) have different shapes and different arborizations at different levels. Tangential, centrifugal and incerta sedis-fibres, which originate either from cell bodies in the cell body layer at the periphery of the outer chiasma or more centrally, terminate in the synaptic region of the lamina. Consideration is given to the clearly demarkated arrangement and length of the branching pattern of retinal and laminal fibres at different levels of the synaptic region of the lamina. In addition, a hypothetical connectivity pattern is discussed.     

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     

Regional distribution of three ultrastructural retinula types in the retina of Cataglyphis bicolor Fabr. (Formicidae,Hymenoptera)

Summary The retina of Cataglyphis bicolor was investigated by electron microscopy. Three types of structurally distinct retinulae were found and mapped throughout the compound eye: Type I is composed of four unpigmented thin cells, four larger pigmented cells as well as a basal ninth cell. Its rhabdom possesses a round cross section and four microvilli directions. This type occupies most of the dorsal two-thirds of the retina. Type II consists of two thin cells, two intermediate cells and four large cells. A basal ninth cell is also present; the rhabdom is as in type I. Type II retinulae are located in the ventral third of the retina. Type III ommatidia are unique within the Hymenoptera: there are four large pigmented cells, four thinner unpigmented cells and a basal ninth cell. The rhabdom, however, has a dumb-bell shaped cross section; two small cells lie at its opposed extremities and the remaining six cells have mutually perpendicular microvilli orientations. This type of retinula is found at the dorso-medial eye margin. Serial sectioning in this region revealed a conical shaped rhabdom without any torsion along the longitudinal axis. The rhabdomere cross section was calculated from distal and proximal thin sections. Angular statistics were applied to the microvilli directions of all three ommatidial types to determine the degree of order. A possible functional significance of the structural specializations of the different eye regions is discussed.Supported by Swiss National Science Foundation, Grant No. 3.814.72 awarded to Prof. Dr. R. Wehner. This work is part of a Ph. D. thesis. I wish to thank Prof. Dr. R. Wehner for continuous support and my colleagues Dr. P. Duelli and Dr. E. Meyer for a fruitful collaboration     

Anther culture of Sorghum bicolor (L.) Moench

The sequence of pollen development from the tetrad stage to the mature tricellular grain was studied in freshly harvested anthers of Sorghum bicolor. This pattern of development was then compared with that occurring during panicle pretreatment and subsequent anther incubation in vitro. It was found that during pretreatment at 7° C mitoses of the vegetative cell were induced in up to 30% of the pollen. During anther incubation procallus development was highly polarised with contributions from both the generative and vegetative cells. After pretreatment at 14 or 20° C the generative cell became detached from the pollen wall and it was not possible to determine whether subsequent development involved only the vegetative cell or both the vegetative and generative cells.Although retarded pollen grains were observed both in vivo and in vitro, and were occasionally seen to divide in culture, they did not appear to be the source of the procalluses produced.     

根癌农杆菌介导的高粱遗传转化体系的研究

采用根癌农杆菌介导法将杀虫晶体蛋白基因cryIA(b)转入高粱胚性愈伤组织中,建立农杆菌转化高粱的遗传转化体系,获得70棵再生植株。经GUS及PCR检测,结果表明,cryIA(b)基因确实转移到高粱恢复系0-30中,报告基因GUS在再生植株中也得到表达。转化植株的抗病性鉴定正在进行中。     

The life history continuum hypothesis links traits of male ants with life outside the nest

Biological control of bruchid beetles, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae), infesting cowpea seeds, Vigna unguiculata (L.) Walpers (Fabaceae), can be performed via augmentative releases of Dinarmus basalis Rondani (Hymenoptera: Pteromalidae) parasitoid wasps. Females of the latter species are therefore likely to experience intense intraspecific competition: they should encounter numerous previously parasitized hosts but also conspecific competitors, with which they may fight to secure hosts on which to lay their eggs. Such contests might therefore disrupt biological control programs. Here, we studied aggressive behavior that D. basalis females show toward conspecific competitors and subsequent host exploitation strategies. We further investigated factors that classically affect contest intensity and outcomes in animals, such as the effect of ownership status, by manipulating the residency period before the intruder's arrival. In addition, we tested the effect of the size of female reproductive tissue (measured in terms of egg load) and the quality of the habitat previously experienced by females (either rich or poor in hosts). These two factors are expected to influence the value that females place on the host and therefore the costs they are willing to pay to win it. Finally, we discussed the consequences of agonistic behaviors on females' host exploitation strategies. Our results suggest that contest competition may actually enhance host control by favoring parasitoid dispersion, rather than disrupting it.